FEMA 259/January 1995 EngineeringPrinciples andPractices for Retrofitting Flood Prone Residential Buildings January 1995 Federal Emergency Management Agency Mitigation Directorate IzMPORTANT To receive periodicupdatesto EngineeringPrinciplesand Practices of Retrofitting Flood- Prone Residential Structures, please fill out and return this enclosed coupon. * E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E U E E E E E E E E E E E E | | EE||| u u u u u - Please add my name to the FEMA mailing list FE.23 and send me updates to Engineering Principlesand Practicesof RetrofittingFlood-ProneResidentialStructures. Name (Please Print) Address City/State/Zip Updates will provided periodically as they are developed to the above user. Place Postage Here Federal Emergency Management Agency P.O. Box 2012 Jessup, MD 20794-2012 Table of Contents Table of Contents ............................... List of Figures ................................. List of Tables ................................. List of Formulas ................................ Nomenclature.................................. Foreword .................................... Acknowledgement. Metrification .................................. Lii Chapter 1: Introduction to Retrofitting ................ How to Use This Manual .......................... Methods of Retrofitting ............................ General Retrofitting Cautions ........................ Retrofitting Process .............................. Chapter II: Regulatory Framework .................. National Flood Insurance Program (NFIP) ................ Community Regulations and the Permitting Process ........... Model Building Codes ............................ Code Compatibility with the NFIP ..................... Chapter III: Parameters of Retrofitting ............ .... Examination of Owner Preferences ........... ...... Community Regulations and Permitting ........ ... .... Technical Parameters ................... .......... Page ... i . .. v .. xv . xvii . xxi .xxxi xxxiii xxxv *. I-1 . . I-1 .. 1-4 . I-27 .1-29 . II-1 . 11-2 II-19 II-21 11-23 III-1 .. III-2 III-16 III-18 Page i * Table of Contents Page Chapter IV: Determination of Hazards ................ . IV-1 Analysis of Flood Related Hazards ..................... . IV-2 Analysis of Non-Flood Related Hazards .................. IV-48 Geotechnical Considerations ......................... IV-55 Chapter V: Benefit/Cost Analysis and .. V-1 Benefit/Cost Analysis Process ............... . V-1 Evaluate Hazards .............................. . V-6 Estimate Potential Damages ......................... . V-9 Identify Costs Associated with Alternatives ................ V-13 Estimate Benefits ............................... V-14 Compute Benefit/Cost Ratio and Net Present Value ........... V-1l9 Select a Method ................................ V-25 AlternativeSelection................ . Chapter VI: General Design Practices .. .V I-1 Elevation..... .. ... ... ....... .. .. ..... VI-E. 1 Relocation..... .. ...... ... .. .... ... .... VI-R.1 Dry Floodproofing . . ..... ..... .... .. ..... VI-D. 1 Wet Floodproofing . ...... ... .. .... .. ..... VI-W.1 Floodwalls .... . .... .. ...... .... .. ..... VI-F.1 Levees....... . ...... . ..... .... .. ..... VI-L.1 Page ii * Table of Contents Page _ Chapter VII: Case Studies .VII-1 Case Study #1: Elevating Houses on Masonry Walls, Masonry Piers and Wood Posts Tug Fork Valley, West Virginia .VII-3 Case Study #2: Elevating Homes on Crawl Space Dry Creek, Goodlettsville, Tennessee .VII-18 Case Study #3: Relocating a Slab-On-Grade House Tampa, Florida .VII-30 Case Study #4: Floodwalls, Levees, and Perimeter Drains Bailey Creek, Madison, Connecticut .VII-54 Case Study #5: Perimeter Floodwall, Henson Creek Prince George's County, Maryland .VII-64 Case Study #6: Wet Floodproofimg a House on a Crawl Space Henson Creek, Prince George's County, Maryland .VII-78 Case Study #7: Dry Floodproofmg a House with a Walk-out Basement, Henson Creek, Prince George's County, Maryland ... VII-90 Case Study #8: Veneer Wall, Dry Floodproofmg Tug Fork Valley, West Virginia .VII-105 Appendices Appendix A: The National Flood Insurance Program .A-1 Appendix B: Glossary of Terms .B-1 Appendix C: Glossary of Resources .C-1 Appendix D: Alluvial Fan Flooding .D-1 Appendix E: Benefit/Cost Analysis of Hazard Mitigation Projects User's Guide .E-1 Page iii * Table of Contents LIST OF FIGURES PAGE v-1 Flooding Along Major Rivers Can Create Widespread Damage I-1 Elevation on Solid Perimeter Foundation Walls .... ............ 1-2 Elevation of Existing Residence on Extended Foundation Walls ....... . xxxi 1-7 1-8 I-9 I-10 I-10 1-3 Elevation on Piers .......... 1-4 Elevation on Posts ......... 1-5 Structure Elevated on Posts .1........ 1-6 Elevationon Piles .............. 1-7 Structure Elevated on Piles .1......... ........................ ........................ .. ... .... .... ... .. ... .. ... .. .. ... .. . I-il 1-12 .. .... ... .. ... .... 1-8 Structure Placed on a Wheeled Vehicle for Relocation to a New Site . . 1-14 1-9 Structure to be Relocated ............................. I-15 I-10 Dry Floodproofed Structure ........................... 1-18 I-l1 Wet Floodproofed Structure ........................... I-20 1-12 Structure Protected by Levee and Floodwall ................. 1-22 1-13 House Protected by a Floodwall ......................... 1-23 1-14 House Protected by a Levee ........................... 1-24 1-15 Primary Steps in the Retrofitting Process ................... I-30 11-1 Typical Floodplain Cross Section . .1.1..................... .II-5 II-2 Typical Flood Profile for Riverine Floodplains . .1.1..............II-7 11-3 Typical Wave Height Transect . 1........................ .. II-9 11-4 Typical FIRM for Riverine Flooding ..1.1.................. .II-10 11-5 Typical FIRM for Coastal Flooding . .1.1.................. .I-10 111-1 Preliminary Floodproofing/Retrofitting Preference Matrix ........ III-4 III-2 Low Point of Floodwater Entry Survey for a Typical Residential Structure................................. III-8 III-3 Retrofitting Screening Matrix ......................... III-19 III-4 Instructions for Retrofitting Screening Matrix ............... III-20 III-5 Photographs Showing Mud Lines on Homes are a Source of Historical Information ................................ III-22 III-6 Hydrostatic Forces ................................ III-22 III-7 Fast-moving Floodwaters Caused Scour Around the Foundation and Damage to the Foundation Wall ................... III-24 III-8 Lateral Forces Resulting From Saturated Soil ............... III-27 III-9 Buoyancy Forces Resulting From Saturated Soil .............. III-27 III-10 Preliminary Building Condition Evaluation Worksheet .......... III-34 IV-1 Flood-Related Hazards . ............................. IV-2 IV-2 House Location on the FIRM ...... .................... IV-3 IV-3 Stream Location on the FIRM ...... .................... IV-4 IV-4 House Location on Flood Profile for Flat Rock Brook ... ........ IV-5 Page v D Table of Contents . . . .V-8 LIST OF FIGURES (continued) IV-5 Coastal FIRM. IV-6 Summary of Stillwater Elevations. IV-7 Illustration of Flood Depth and Design Depth .. IV-8 Hydrostatic Forces. IV-9 Hydrostatic Force. IV-10 Saturated Soil Hydrostatic Forces. IV-11 Combination Soil/Water Hydrostatic and Buoyancy Forces . IV-12 Hydrostatic Force Computation Worksheet ................. IV-13 Example Hydrostatic Force Computation . IV-14 Hydrodynamic and Impact Forces . IV-15 Equivalent Hydrostatic Force Computation Worksheet. IV-16 Example Equivalent Hydrostatic Force Computation. IV-17 Hydrodynamic Force (High Velocity) Computation Worksheet IV-18 Example Hydrodynamic Force (High Velocity) Computation IV-19 Impact Force Computation Worksheet .................... IV-20 Example Impact Force Computation . IV-21 Rectangular Area Enclosed by a Floodwall or Levee . IV-22 Rectangular Area Partially Enclosed by a Floodwall or Levee PAGE . IV-6 . IV-7 . IV-9 IV-10 IV-11 IV-13 IV-16 IV-18 IV-19 IV-20 IV-23 IV-24 IV-27 IV-28 IV-33 IV-34 IV-36 IV-37 IV-40 IV-48 IV-49 IV-49 IV-51 IV-52 IV-57 IV-61 IV-61 IV-63 IV-64 IV-66 IV-67 V-2 IV-23 Telluride, Colorado, Alluvial Fan . IV-24 Non-Flood-Related Natural Hazards. IV-25 Wind Design Process . IV-26 Wind Design Process Illustration . IV-27 Seismic Design Process ................. IV-28 Seismic Design Process Illustration . IV-29 Geotechnical Considerations Decision Matrix. IV-30 Local Scour at Piers, Piles, and Posts . IV-31 Scour Action on a Ground-Level Building. IV-32 Process for Estimating Potential Scour Depth. IV-33 Flow Angle of Attack . IV-34 Terminating Strata . IV-35 Additional Embedment. V-1 Benefit/Cost Analysis Process ........................... V-2 Critical Steps in Evaluating Flood Hazards .V-6 V-3 Discharge Versus Elevation (Rating Curve) .V-6 V-4 Critical Steps in Evaluating Flood Hazards V-5 FIA Depth-Damage Data Table .V-10 V-6 Types of Benefits Evaluated .V-14 V-7 Critical Steps in Benefit/Cost Ratio Analysis .V-20 V-8 Factors Weighing on Alternative Selection .V-25 V-9 Preference Ranking Worksheet .V-27 V-10 Floodproofing Measure Component Takeoff Guide V-li Detailed Cost Estimating Worksheet .V-32 Page vi .V-29 * Table of Contents LIST OF FIGURES (continued) PAGE VI-1 Design Process ........... ............... ....... VI-2 VI-2 Topographic and Site Survey . ....... VI-6 VI-3 Mechanical, Electrical, Plumbing, and Related Building SystemsData Sheet ................ . . ...... VI-11 VI-4 Structural Reconnaissance Worksheet. ....... VI-19 ....... VI-20 Loading ... ..VI-5FoundationSystem..... VI-6 VI-7 VI-8 VI-El VI-E2 VI-E3 VI-E4 VI-E5 VI-E6 VI-E7 VI-E8 VI-E9 VI-E10 VI-Ell VI-E12 VI-E13 VI-E14 VI-E15 VI-E16 VI-E17 VI-E18 VI-E19 VI-E20 VI-E21 VI-E22 VI-E23 VI-E24 VI-E25 Building Weight Estimating Worksheet ............. ...>... VI-29 Column Tributary Area ........ ....... VI-32 Wall/Girder Tributary Area. ....... VI-32 Existing Wood-Frame Residence With Crawl Space . Install Network of Steel "I" Beams . Lift Residence and Extend Foundation Walls; Relocate Utility and Mechanical Equipment Above Flood Level . Raising a Wood-Frame-Over-Crawl-Space Structure. Set Residence on Extended Foundation and Remove "I" Beams . Install Network of Steel "I" Beams . Raising a Wood-Frame-Over-Crawl-Space Structure on Piers . Set Residence on Reinforced Piers ..................... Relocate Utility and Mechanical Equipment Above Flood Level . Creation of a New Masonry Enclosed Area on Top of an Abandoned Basement ................... ...... Creation of a New Masonry Open Area on Top of an Abandoned Basement (Piers) .............. ...... Set Residence on Reinforced Piers ............... ........ Existing Slab-on-Grade Wood-Frame Residence ....... ...... Install Steel "I" Beam Network and Prepare to Lift Walls . ...... Lift Residence and Extend Masonry Foundation Wall; Relocate Utility and Mechanical Equipment Above Flood Level ..... Raising a Slab-on-Grade Wood Frame Structure Without the Slab Set Residence on New Foundation and Remove "I" Beams ...... Lift Residence and Extend Masonry Foundation; Relocate Utility and Mechanical Equipment Above Flood Level ..... Raising a Slab-on-Grade Wood-Frame Structure Without the Slab Intact ............................. Set Residence on New Foundation and Remove ,I, Beams ...... Excavate Under Existing Slab and Install Network of Steel "I" Beams ............................... Raising a Slab-on-Grade Wood-Frame Structure With the Slab .... Set Residence on New Foundation and Remove "I" Beams ...... Design Process for an Elevated Structure ................. Elevation Field Investigation Worksheet .................. VI-E.3 VI-E.4 VI-E.5 VI-E.6 VI-E.7 VI-E.8 VI-E.9 VI-E. 10 VI-E.12 VI-E.13 VI-E. 14 VI-E. 15 VI-E. 18 VI-E. 19 VI-E.20 VI-E.21 VI-E.22 VI-E.23 VI-E.24 VI-E.25 VI-E.26 VI-E.27 VI-E.28 .VI-E. 30 VI-E.33 Page vii * Table of Contents LIST OF FIGURES (continued) PAGE VI-R1 VI-R2 VI-R3 VI-R4 VI-R5 VI-R6 VI-R7 VI-R8 VI-R9 VI-R10 VI-Rl1 VI-R12 VI-R13 VI-R14 VI-R15 VI-R16 VI-R17 VI-R18 VI-R19 VI-R20 VI-R21 VI-D1 VI-D2 VI-D3 VI-D4 VI-D5 VI-D6 VI-D7 VI-D8 House Relocation ................................. VI-R. 1 Relocation Process .VI-R.2 Relocation/Elevation Contractor Selection Checklist .VI-R.5 When a house is too large to be relocated in one piece, careful planning is necessary to cut the structure and move the pieces separately .VI-R.9 Clearing Pathways Beneath the Structure for Lifting Supports .. . .. VI-R. 11 Pathways for Lifting Beams .VI-R. 14 Beams Supported by Cribbing are Placed at Critical Lift Points .VI-R. 15 Structure is Separated From Foundation .VI-R. 16 Excavation of Temporary Roadway .VI-R. 17 Trailer Wheel Sets are Placed Beneath the Lifting Beams .VI-R. 18 House is Lowered onto Trailer Wheel Sets .VI-R. 19 Tractor is Used to Pull House to Street .VI-R. 19 As house is pulled to street level, wheels are continually blocked to prevent sudden movement ................. House is Stabilized and Connected to Trailer ............ Journey to New Site Begins ...................... Foundation Preparation at New Site ................. Support Cribbing is Placed ....................... Materials for New Foundation are Readied ............. New Foundation Wall Construction Begins ............. Once foundation walls are completed, house is lowered ntidrcnnecteri tn fniinribtirn -1w1WiIIM_;WtUXl>LlJl...................... A ... VI-R.20 ... VI-R.20 ... VI-R.21 .... VI-R.22 ... VI-R.23 ... VI-R.23 ... VI-R.24 Final Preparations for Backfilling and Landscaping ........... Process of Selection and Design ....................... The best way to seal an existing brick-faced wall is to add an additional layer of brick with a seal in between. Just sealing the existing brick is also an option ......... A wrapped house sealing system can be used to protect against low level flooding ...................... A shield hinged at its bottom could prevent low level flooding from entering a garage or driveway ........... A door opening may be closed using a variety of materials for shields ............................... A shield can help prevent low level flooding from entering through a doorway .......................... VI-R.25 VI-R.25 VI-D.2 VI-D.6 VI-D.7 VI-D.8 VI-D.8 VI-D.9 Where a window is exposed to a flood, bricking up the opening could eliminate the hazard ............. Dry floodproofed homes should have an effective drainage system around footings and slabs to reduce water pressure on foundation walls and basements ..... ....... .I. .. .VI-D. 10 Page viii m-Table of Contents LIST OF FIGURES (continued) PAGE VI-D9 VI-D10 VI-D11 VI-D12 VI-D13 VI-D14 VI-D15 VI-D16 VI-D17 VI-D18 VI-D19 VI-D20 VI-D21 VI-D22 VI-D23 VI-D24 VI-D25 VI-D26 VI-D27 VI-D28 VI-D29 VI-D30 VI-D31 VI-D32 VI-Wi VI-W2 VI-W3 VI-W4 VI-W5 VI-F1 VI-F2 Drain System Around a Slab-on-Grade House. Existing Building Structural Evaluations. Typical Design Strip ........ ... Typical Slab Uplift Failure. Selection of Sealants/Coatings. Selection and Design of Wrapped Sealant Systems. Plain View of Wall Section ......................... Selection/Design of a Brick Veneer Sealant System. Selection/Design of Plate Shields ...................... Typical Residential Masonry Block Wall Construction. Common Faults Contributing to Seepage Into Basements Typical French Drain System . Typical Exterior Underdrain System with Sump Pump Showing Two Alternative Configurations in the Side View . Details of a Combination Underdrain and Foundation Waterproofing System. Typical Interior Drain Systems. Types of Sump Pumps . Sump Pump Field Investigation Worksheet. Sump Pump Design Process . Typical Sump Detail ........................... BackwaterValve..... I ......... . .. Floor Design With Ball Float Check Valve ............. . .. Backwater Valve Selection ....................... . .. Backwater Valve Field Investigation Worksheet ... . . . . . . .. Emergency Power Design Process ........... . . . . . . .. Typical Opening for Solid Foundation Wall ...... ... .. NFIP-Compliant Residential Building Built on Solid Foundation Walls with Attached Garage ... ..... Elevated Air Conditioning Compressor ........ .. ..... Flood Enclosure Protects Basement Utilities from Shallow Flooding ................. .... Wet Floodproofing Field Investigation Worksheet .. ......... Typical Residential Floodwall .............. . . . . . . . . . Typical Residential Floodwall .............. . . . . . . . . . VI-D.11 VI-D.15 VI-D.17 VI-D.19 VI-D.24 VI-D.25 VI-D.27 VI-D.29 VI-D. 33 VI-D.50 VI-D.51 VI-D.52 VI-D.54 VI-D.55 VI-D.57 VI-D.58 VI-D.61 VI-D.63 VI-D.65 VI-D.73 VI-D.73 VI-D.74 VI-D.75 VI-D. 82 V I-W .4 V I-W .5 V I-W .9 V I-W .10 VI-W.12 . VI-F.2 . VI-F.2 Page ix * Tableof Contents LIST OF FIGURES (continued) PAGE VI-F3 VI-F4 VI-F5 VI-F6 VI-F7 VI-F8 VI-F9 VI-Flo VI-Fi 1 VI-F12 VI-F13 VI-F14 VI-F15 VI-F16 VI-F17 VI-F18 VI-F19 VI-F20 VI-F21 VI-F22 VI-F23 VI-F24 VI-F25 VI-F26 VI-F27 VI-F28 VI-F29 VI-F30 VI-F31 VI-F32 VI-F33 VI-F34 VI-F35 VI-F36 VI-L1 VI-L2 VI-L3 VI-L4 VI-L5 VI-L6 Gravity and Cantilever Floodwalls . Buttress and Counterfort Floodwalls . Stability of Gravity Ploodwalls... Concrete Cantilever Floodwall Reinforcement. Stability of Cantilever Floodwalls. Typical Reinforced Concrete Floodwall. Typical Section of a Brick-Paced Concrete Floodwall. Typical Brick-Faced Concrete Floodwall. Seepage Underneath a Floodwall . .... .... VI-F.3 . ... .... VI-F.3 . ... .... V I-F.4 .... ....VI-F.5 ........VI-P.6 ........V I-F.7 ........VI-F.8 ... .. VI-F.9 ....VI-F.12 Reducing Phreatic Surface Influence by Increasing Distance from Foundation to Ploodwall Floodwall Design Process ....... Failure by Sliding ............. Failure by Overturning .......... Failure Due to Excessive Pressure ... Forces Acting on a Floodwall ...... Typical Reinforcing Steel Configuration Typical Floodwall Closures ....... Closure Variables ............. Sample Patio Drainage to an Outlet ... Sample Patio Drainage to a Sump .... Typical Gravity Floor Drain ....... Typical Patio Sump Pump Installation . Typical Patio Gravity Floor Drain Installation Typical Floodwall With Check Valve ..... Waterstop.............. Floodwall to House Connection . Typical Cosmetic Facings .... Floodwall Supporting Columns Floodwall Supporting Columns Typical Step Detail ........ Typical Floodwall Steps ..... Typical Floodwall Steps ..... Typical Floodwall Landscaping Floodwall Inspection Worksheet . Typical Residential Levee ............. Drainage Toe Details ... ... ... .. . .............. .. ... ... ... ... .. . ... ... .. ... ... ... .. ... ... ... . ... ... .. ... ... ... ... .. .... .. ... .. ... ... .. .. ... ... ... . . .... .. ... ... . .. .. ....... ... . .. ... ... . ... .. ... . .. ... ... ...... . .. ... ... ....... .. .... .. .V I-F.63..... ... ... ... V I-F.64 ..... ... ... ... V I-F.65 ..... ...... .. .VI-F.65 ..... ... ... ... ... V I-F.66 .. ... ... ... ... ... ... . V I-F.13 VI-F.315 ......... VI-F. 16 V I-F.16 V I-F.19 ... V I-F.35 ... V I-F.44 ... V I-F.45 ... V I-F.53 ... VI-F.54 ... VI-F.54 .... VI-F.55 .... VI-F.57 ..... V I-F.60 ..... VI-F.61 V I-F.63 .................... . .. ... . Drain Pipe Extending through Levee ........... . .. ... V I-L.10 ... Interior Storage Area .................... .. VI-L.ll .... Compacted Lifts ....................... .. V I-L .15 .... Access over the Levee ................... .. VI-L.16 .... 0 Page x P Table of Contents LIST OF FIGURES (continued) PAGE VII-1.1 VII-1.2 VII-1.3 VII-1.4 VII-1.5 VII-1.6 VII-1.7 VII-1.8 VII-1.9 VII-2. 1 VII-2.2 VII-2.3 VII-2.4 VII-2.5 VII-2.6 VII-2.7 VII-3.1 VII-3.2 VII-3.3 VII-3.4 VII-3.5 VII-3.6 VII-3.7 VII-3.8 VII-3.9 VII-3. 10 VII-3. 11 VII-3.12 VII-3.13 VII-3.14 VII-3.15 VII-3.16 VII-3.17 VII-3.18 VII-3.19 VII-3.20 VII-3.21 Tug Fork Valley .............. Typical Wall Detail Section ....... Interior Column Detail .......... Flood Louver Detail ............ Masonry Pier Plan ............. Masonry Pier Detail Section ....... Insulated Utility Pipe Chase Detail Pipe Chase Detail Section ........ Wood Post/Beam Detail Section ..... Dry Creek Project .......................... Typical Home Raised About Two Feet Typical Home Raised About Five Feet . ..... .. .... ...... .... .. ...... .... .. ...... .... .. ..... . .... .. ..... . .... .. ... ... .... .. ... ... .... .. ... . .. ...... VII-4 ..... .VII-10 VII-11 ..... . ..... .VII-11 VII-12 ..... . .. V II-14 V II-15 V II-15 V II-16 VII-19 ...... .............. ...... VII-27 .............. ...... VII-27 Example of a Home Raised With the Brick Veneer in Place During Construction .................... ...... VII-28 Example of a Home Raised With the Brick Veneer in Place Completion .......................... ...... VII-28 Provisions for equalization of hydrostatic head was accomplished with foundation vents and/or flexible flaps on crawl- space access door. . ......... . .VII-29 Example of a Home Raised With Air Conditioner Compressor Unit VII-29 VII-31 VII-32 VII-33 VII-34 VII-34 VII-35 VII-36 VII-36 VII-37 VII-37 VII-38 ... VII-40 ... . VII-40 .... VVII-41 VII-42 ... . VII-43 .... VVII-43 .... VVII-44 .... VII-42 VII-45 VII-45 ... Page xi on Elevated Platform ............. Temporary Supports for the Slab ........ Fireplaces Require Special Attention ...... Timber Cribbing .................. Piers Cut Away Using Air Saw ......... Piers From Original Foundation ......... Cutting Reinforcing Steel ............. Garage Floor Slab Removed ........... Holes in Garage Wall to Insert Steel Beams Excavation Below Slab to Allow Access .... Excavation and Tunneling Completed ..... Slab Cut With a Street Saw ........... Long Nosed Shovel Attachment ......... Perimeter Grade Beam Being Removed .... Snoot Being Used to Tunnel Under Slab .... Shims Used on Underside of Slab ........ Wedges Used on Underside of Slab ...... Relocated Concrete Block Home ........ Concrete Block Counterbalance ......... New Piers and Wood Cribbing ......... Exterior Concrete Masonry Block Wall .... Breakaway Exterior Walls ............ .. ...... .. ... .. ... . .. ...... . .. ..... .. .. ..... . . .. ..... .. .. ..... .. .. ... .. .. . ...... .. . . ..... .. ..... . ... ...... .. . ...... ... ..... ... . ..... .... ..... ... . ... .. .... *- Table of Contents LIST OF FIGURES (continued) PAGE VII-3.22 Interior Shoring. VII-47 VII-3.23 Plastic Sheeting for Weather Protection . VII-47 VII-3.24 One Section of the House has been Raised Preparatory to Insertion of Dollies .................... . . VII-48 VII-4. 1 Surface Water Problem (Before) VII-56 VII-4.2 Surface Water Problem (After) . . . . . . . . . .. . . . . . VII-56 VII-4.3 Site Plan ................ . . . . . . . . . .. . VII-58 VII-4.4 Typical Detail Section Floodwall . . . . . . . . . .. . . . . VII-59 .. VII-4.5 Typical Detail Section of Backfilled LFloodwall . . . . . . VII-59 VII-4.6 Patio Area Sump Pump Detail ... . . . . . . . . . .. . . . . VII-60 VII-4.7 Footing Drain Detail ........ . . . . . . . . . .. . . . . VII-60 VII-4.8 Completed Patio Floodwalls .... I . . . . . . .. .. . VII-61 .. VII-4.9 Site Plan: House on Opposite Side Of Bailey Creek-and . . . Engineering Solutions ... .. . . . . . . . . .. . . . . VII-62 VII-4. 10 Typical Drain Detail ......... . . . . . . . . . .. . . . . VII-63 VII-4. 11 Sump Pump and Sump Detail ... . . . . . . . . . .. . VII-63 VII-5. 1 Location Plan ........................ ... .. VIL-68 VII-5.2 Preexisting Slab-on-Grade Construction Detail .... VII-69 VII-5.3 Site Plan ........................... VII-72 VII-5.4 Typical Floodwall Detail Section ............ . VII-73 VII-5.5 Footer Detail ........................ VII-74 VI1-5.6 Wall-to-House Connection Detail ............ I .. .. I VII-74 VII-5.7 Drain Detail ......................... ..... ... VII-75 VII-5.8 Sump Detail .............. . . . . . . ..... ... VII-75 VII-5.9 Floodwall Steps and Landscaping Timber ....... . . . . . . VII-76 VII-5. 10 Sump Pump Outlet and Raised Air Conditioner Unit . .. . . .... ... VII-76 VII-5. 11 Completed Project ..................... . . . . . . VII-77 VII-6. 1 Location Plan .................. ... ... .. ... .. V II-79 .... VII-6.2 Preexisting Foundation Wall Section Detail ... ... .. ... .. V II-80 .... VII-6.3 Dry Floodproofing Calculations ....... ... ... ... .. .. V II-81 .... VII-6.4 Wet Floodproofing Calculations ....... .. .I .... .. .. V II-83 ..... VII-6.5 Site Plan ..................... ... .. ... ... . V II-87 ..... VII-6.6 Block Vent Detail ............... ... ... .. ... . V II-88 ..... VII-6.7 Access Door Detail .............. .. ... ... .. . V II-88 ...... VII-6.8 Anchorage Detail for Sheds ......... ... .. ... ... .. . V II-89 ... VII-7. 1 Location Plans ................. ... ... .. ... ... V II-91 ... VII-7.2 Dry Floodproofing Calculations ....... . ... .. ... ... ... .. VII-7.3 Preexisting Walk-out Basement Foundation' Wall Detail Section .... . VII-95 VII-7.4 Site Plan ..................... ... .. ... ... .. V II-96 .... Page xii * Table of Contents LIST OF FIGURES (continued) PAGE VII-7.5 VII-7.6 VII-7.7 VII-7.8 VII-7.9 VII-7. 10 VII-7. 11 VII-7.12 VII-7.13 VII-7.14 VII-7.15 VII-7.16 VII-7.17 VII-8.1 VII-8.2 VII-8.3 VII-8.4 D-1 D-2 D-3 D-4 D-5 D-6 D-7 D-8 D-9 D-10 D-11 D-12 Concrete Patio, Replacement Floodwall, and New Access for Basement Detail ................... VII-97 Step and Wall Detail Elevations ...... . . . . .. ..... VII-98 Concrete Floodwall Detail ......... . . . . .I ..... .VII-99 Downspout Connection to Drain Detail . . . . .. ..... VII-99 Floodwall Connection to House Detail . . . . . . .. .... VII-100 Floodwall Supporting Columns Detail ........... .VII-100 Step Detail ................ ........... .VII-101 Step Detail ................ ........... .VII-101 Sump Pump Detail ............ ........... VII-102 Stair Section ............... ........... .VII-102 Air Conditioning Pad and Sump Pump ........... VII-103 Floodwall and Supporting Columns . . ........... VII-103 Stairs and Supporting Columns .... ........... .VII-104 o Veneer Wall Detail Section ......... . . . . . . .. . . ... VII-106 Veneer Wall Metal Anchor Detail Section . . . . . . . . . ... VII-106 Aluminum Flashing Detail Section .... . . . . . . . . . ... VII-107 Watertight Closure Section ......... . . . . . . . . . .. . VII-108 Telluride, Colorado Fan .... I........ D-2 Alluvial Fan Flooding Damage, Telluride, Colorado . D-2 Rancho Mirage, California Fan Damage (1979) . D-3 Oblique View of an Alluvial Fan . D-3 Reinforced Upfan Walls . D-22 Reinforced Upfan Walls . D-22 Floodwall Protecting Residence in Colorado . D-23 Debris Flow Levee . D-24 Diversion Levee in Colorado . D-25 Typical Subdivision Plot Plan . D-26 Typical Rural Plot Plan . D-27 Typical Dispersion Design . D-28 Page xiii Table of Contents T LIST OF TABLES I-1 Advantages 1-2 Advantages 1-3 Advantages I-4 Advantages I-5 Advantages and Disadvantages and Disadvantages and Disadvantages and Disadvantages and Disadvantages of Elevation .................. of Relocation .............. of Dry Floodproofing ............ of Wet Floodproofing ............ of Floodwalls and Levees ... II-1 Typical Summary of Discharges Table .................... II-2 Typical Summary of Coastal Stillwater Elevations ............. II-3 Model Code Groups ............................... II-4 Model Codes/NFIP Requirements: Items to be Reconciled ....... III-1 Elevation and Relocation Cost Guide ..................... PAGE 1-13 1-16 I-19 1-21 1..... 1-25 * . 11-6 . . II-8 . 11-22 . II-24 III-10 III-2 Floodwalls and Levees Cost Guide ...................... III-1 1 III-3 Dry Floodproofing Cost Guide ........................ III-12 III-4 Flood Shields Cost Guide ............................ III-12 III-5 Preliminary Cost Estimating Worksheet ................... III-13 III-6 Flood Risk .................................... III-14 IV-1 Flood Data Summary .............................. . IV-6 IV-2 Effective Equivalent Fluid Weight of Soil(s) ................ IV-13 IV-3 Soil Type Definitions Based on USDA Unified Soil Classification IV-14 IV-4 Drag Coefficients ................................ IV-21 IV-5 Freeboard and Factor of Safety Recommendations ............. IV-45 IV-6 Typical Bearing Pressure by Soil Type (from Table IV-3) ........ IV-59 IV-7 Scour Factor for Flow Angle of Attack, K ................. IV-65 IV-8 Typical Values of Coefficient of Permeability k for Soils ........ IV-71 VI-1 Approximate Bearing Capacity for Masonry Materials .... ...... VI-24 VI-2 Wall Lateral Support Requirements ...... ................ VI-24 VI-3 Weights of Construction Types ....... ................. VI-28 VI-D1 Essential Equipment/Appliances to Operate From Emergency Power Source .. ... ... . .... . ... .. .. .VI-D.79 VI-D2 Typical Electrical Appliance Loads .... ................. VI-D.82 VI-D3 Example of Maximum Generator Sizing Procedure ... ........ VI-D.83 VI-D4 Example Step Sequence Manual Start Minimum Generator Size . . . VI-D.84 VI-D5 Minimum Panel Bus Sizes .......................... VI-D.89 VI-F1 Soil Factors for Floodwall Design ..................... VI-F. 17 VI-F2 Assumed Soil Factors for Simplified Floodwall Design ......... VI-F.40 VI-F3 Typical Floodwall Dimensions for Clean, Dense, Sand and Gravel (Soil Types GW, GP, SW, SP) ........... VI-F.41 Page xv i Table of Contents LIST OF TABLES (continued) PAGE VI-F4 Typical Floodwall Dimensions for Dirty Sand and Gravel of Restricted Permeability Soil Types: (GM, GM-GP, SM, SM-SP) . VI-F.42 VI-F5 Moment (j) and Deflection (a) Coefficients . VI-F.48 VI-L1 Stone Protection Layer Guidance ...................... . VI-L.9 VI-L2 Cost Estimate Example . VI-L. 12 VI-L3 Levee Cost Estimating Worksheet . VI-L. 13 VII-1.1 RetrofittingforStructureElevation........... .. ... .. . .VII-7 Cost VII-2. 1 DryCreekFloodproofingProject ................ Summary . VII-21 VII-2.2 Cost Analysis Table .............................. VII-24 VII-2.3 Post-ProjectQuestionnaire ... .. .. . VII-26 Results ............. . VII-3. 1 Detailed Cost Estimate Elevation of a 36x36 (1296 sf) One-Story Home 2 Feet Above Ground ..................... VII-52 VII-3.2 Detailed Cost Estimate Elevation of a 36x36 (1296 sf) One-Story Home 10 Feet Above Ground ..................... VII-53 VII-8. 1 Floodproofing Cost for a Veneer Wall ................. . . VII-109 Page xvi T Table of Contents LIST OF FORMULAS IV-1 IV-2 IV-3 IV-4 IV-5 IV-6 IV-7 IV-8 IV-9 IV-10 IV-li IV-12 IV-13 IV-14 IV-15 IV-16 IV-17 IV-18 IV-19 IV-20 IV-21 IV-22 IV-23 IV-24 IV-25 IV-26 V-1 V-2 V-3 V-4 V-5 V-6 V-7 V-8 V-9 V-10 V-11 V-12 V-13 V-14 Flood Depth.................................... Flood Protection Elevation .. ... .............. Floodproofing Design Depth ......................... Lateral Hydrostatic Forces ........................... Saturated Soil Hydrostatic Forces ....................... Combined Water and Soil Forces ....................... Cumulative Lateral Hydrostatic Force .................... Buoyancy Force ................................. Conversion of Low Velocity Flow to Equivalent Head .......... Conversion of Equivalent Head to Equivalent Hydrostatic Force ............................ Total Lateral Hydrostatic Force ........................ High Velocity Hydrodynamic Pressure .................... Total Hydrodynamic Force ........................... Normal Impact Force .............................. Special Impact Forces.............................. Runoff Quantity in an Enclosed Area .................... Runoff Quantity from Higher Ground Into a Partially Enclosed Area .............................. Seepage Flow Rate Through a Levee or Floodwall ............ Minimum Discharge for Sump Pump Installation ............. Bulking Factor ..... Bulin ................................ Fcto Specific Weight of Water-Sediment Mixture ................ Recommended Freeboard ............................ Allowable Bearing Capacity .......................... Maximum Potential Scour at Embankment Toe ............... Maximum Potential Scour at Structure .................... Volume of Seepage ............................... Scenario Damages ................ . . . . . . . . . . . . . Building Damages ................ . . . . . . . . . . . . . Contents Damages ................ . . . . . . . . . . . . . Displacement Costs ............... . . . . . . . . . . . . . Rental Income Losses .............. . . . . . . . . . . . . . Expected Annual Damages ........... . . . . . . . . . . . . . Expected Avoided Damages .......... . . . . . . . . . . . . . Expected Annual Benefits ........... . . . . . . . . . . . . . Present Worth Factor .............. . . . . . . . . . . . . . Present Value of Estimated Annual Benefits . . . . . . . . . . . . . Present Value of Estimated Annual Costs .. . ..... ..... .. Benefit/CostRatio ....... ...... . . . . . . . . . . . . . Net Present Value ................ . . . . . . . . . . . . . Adjusting Unit Cost for Local Communities . . . . . . . . . . . . . PAGE . IV-8 . IV-8 . IV-9 IV-1l IV-12 IV-15 IV-16 IV-17 IV-21 IV-22 IV-22 IV-25 IV-25 IV-30 IV-31 IV-37 IV-38 IV-38 IV-39 IV-42 IV-43 IV-44 IV-58 IV-63 IV-64 IV-69 V-14 . V-15 V-15 V-16 V-16 V-17 V-17 .V-18 .V-19 V-20 .V-20 .V-21 V-21 V-30 Page xvii : i Table of Contents LIST OF FORMULAS (continued) PAGE VI-1 Determining Footing Size. VI-21 VI-2 Maximum Loading of Existing Footing. VI-21 VI-3 Bearing Capacity of an Existing Concrete Masonry Foundation Wall ............................. VI-22 VI-4 Slenderness Ratio . VI-23 VI-5 Calculation of Live Load . VI-30 VI-6 Calculation of Tributary Area for Load-bearing Walls .......... VI-31 VI-7 Calculation of Tributary Area for Center Girder . VI-32 VI-8 Calculation of Tributary Area for Columns . VI-32 VI-9 Calculation of Wall/Column Loads. VI-33 VI-10 Calculation of Self Weight of Wall/Column. VI-34 VI-i1 Calculation of Total Load Carried by the Wall or Column to the Footing or Foundation ................ VI-34 VI-D1 Total Discharge Head ............................. NrI-D.66 VI-D2 Head Loss Due to Pipe Fittings ....................... N1-D.67 VI-W1 Buoyancy Force on a Tank ............. VI-W.36 VI-W2 Concrete Volume Required to Offset Buoyancy VI-W.37 VI-F1 Buoyancy on a Floodwall .......... ... ... .. .. VI-F.20 ..... VI-F2 Floodwall Weight .............. I. ... ... ... ... . V I-F.21 VI-F3 Footing Weight ................ .. ... ... ... . V I-F.21 ... VI-F4 Weight of Soil Over Floodwall Toe ... ... ... .. ... . V I-F.22 ... VI-F5 Weight of Soil Over Floodwall Heel ... .al ... ... ... ... V I-F.22 ... VI-F6 Weight of Water Above Floodwall Heel ... ... ... ... V I-F.23 ... VI-F7 Total Gravity Forces Per Linear Foot of's .............. VI-F.23 VI-F8 Net Vertical Force ...... ........ ... ... ... .. V I-F.23 .... VI-F9 Sliding Forces ................ .... .. ... .. V I-F.24 .... VI-FlO Frictional Force ............... ... .. ... .. V I-F.25 ..... VI-Fll Cohesion Force ................ ... ... ... . VI-F.26 ..... VI-F12 Saturated Soil Force Over Floodwall Toe .I ... ... ... . V I-F.27 ..... VI-F13 Sum of Resisting Forces to Sliding .... .. ... ... ... . V I-F.27 ... VI-F14 Factor of Safety Against Sliding ...... ... ... .. ... . V I-F.28 ... VI-F15 Sum of Overturning Moments ....... ... ... ... .. . V I-F.29 ... VI-F16 Sum of Resisting Moments ......... ... ... ... ... V I-F.30 ... VI-F17 Factor of Safety Against Overturning . . ... ... ... ... V I-F.31 ... VI-F18 Eccentricity ... ... .... .................. ... .. VI-F.32 Pressure ... VI-F.33 ....VI-F19 Soil ........ . . ... .. ... VI-F20 Cross-Sectional Area of Steel ....... ... ... ... .. VI-F.34 .... VI-F21 Plate Thickness due to Bending Stresses . . ... ... ... .. V I-F.47 .... VI-F22 Plate Thickness due to Deflection Stresses ... ... ... .. V I-F.47 .... VI-F23 Bending Moment ................ .. ... ... .. V I-F.49 ..... VI-F24 Bending Stress ................. .. ... ... ... ... . Page xviii i Tableof Contents LIST OF FORMULAS (continued) PAGE VI-F25 Shear Force ................. .. V I-F.50 VI-F26 ... V I-F.50 Shear...... . .. Stress VI-F27 Plate Deflection for a One-Way Span V I-F.51 VI-F28 Allowable Deflection ........... V I-F.51 VII-1. 1 Dry Creek House Raising Costs ..... ..... V II-23 Page xix * Table of Contents NOMENCLATURE a Deflection coefficient Moment coefficient ly Specific weight of water IyS Specific weight of the water/sediment mixture 'Ysol Unit weight of soil or Allowable stress for closure plate material Ab Computed deflection Aba Allowable deflection p Mass density of water a Diameter of post A Area a,b Span lengths between the walls and center girder AB Expected Annual Benefits Aasbc Specific Area enclosed by a floodwall/levee A,, Column tributary Area AD Expected Annual Damages Ag Center girder tributary Area Ah Width of footing heel As Cross-sectional Area of reinforcing steel required per foot width of wall At Column tributary Area AVD Expected Avoided Damages AW Wall tributary Area Page xxi * Table of Contents NOMENCLATURE (continued) b Width of object (structure) perpendicular to flow B Width of footing BCR Benefit/Cost Ratio BD Scenario Building Damages BF Bulking Factor BFE Base Flood Elevation BRV Building Replacement Value c Residential terrain runoff coefficient C Width of footing toe Cd Drag Coefficient CD Scenario Contents Damages Cf Coefficient of friction CF Cubic Foot CFR Code of Federal Regulations cfs Cubic feet per second CR Building Contents Replacement value Crs Rolling shear Constant Cs Allowable soil Cohesion value C:, Concentration of sediment in the fluid mixture by percent of volume d Depth of flooding D Depth of saturated soil over which hydrostatic forces are considered Page xxii * Table of Contents NOMENCLATURE (continued) dl. 5Q design Depth of flooding from a discharge 50% greater than the design discharge Da Height of vertical foundation member above grade Db Depth of burial of vertical foundation member DD Displacement Days df Distance between reinforcing steel and floodwall face opposite retained material dh Equivalent head due to low velocity flood flow Dh Depth of soil above the floodwall heel DIS Scenario Displacement costs DL Dead Load dQ design Depth of flooding from the design discharge DRR Daily Rental Rate Ds Difference in elevation between the bottom of the sump and the point of discharge Dt Depth of soil above the floodwall toe e Eccentricity E Modulus of Elasticity EABpv Present value of Estimated Annual Benefits EAE Expected annual number of floods of a given depth EACpV Present value of Estimated Annual Costs ECCpV Present value of Engineering and Construction Costs associated with a retrofitting measure Page xxiii * Table of Contents NOMENCLATURE (continued) ECD Expected Contents Damage EFF Effectiveness of mitigation measure in reducing expected damages from a flood of a given depth FA Floor Area of building in square feet f Freeboard (factor of safety) fb Bending stress Fb Vertical hydrostatic Force (buoyancy) FBFM Flood Boundary and Floodway Map Fb1 Buoyancy Force acting on a floodwall heel FbZ Buoyancy Force acting on a floodwall toe fo Bearing capacity of masonry Fc Cohesion Force between the footing and the soil Fd Hydrodynamic Force Fdh Equivalent hydrostatic Force due to low velocity flood flow Fdif Differential soil/water Force FE Flood Elevation for a specific flood frequency FEMA Federal Emergency Management Agency Ff, Frictional Force between the bottom of the footing and the soil Fh Lateral hydrostatic Force from standing water FH Cumulative lateral Hydrostatic Force FIA Federal Insurance Administration FIRM Flood Insurance Rate Map Page xxiv * Table of Contents NOMENCLATURE (continued) FIS Flood Insurance Study Normal impact load Fp Saturated soil Force over the toe of the footing FPE Flood Protection Elevation FPL Flood Protection Level fps Feet per second FR Sum of Resisting Forces to sliding fr. Shear stress F., Special impact load FSS Maximum Shear Stress FS Factor of Safety Fsat Lateral hydrostatic Force from saturated soil FS(07) Factor of Safety against Overturning FS(SL) Factor of Safety against Sliding Fv Net Vertical Force g Acceleration of gravity gpm Gallons per minute GS Lowest Ground Surface elevation (grade) or other reference feature (slab or footing) adjacent to structure h Distance from bottom of structure to water level H The floodproofing design depth over which flood forces are considered h. Height of closure Page xxv i Tableof Contents NOMENCLATURE (continued) if fittings Head loss through the pipe fitting(s) lifpipe Head loss due to pipe friction H, Height of unbraced foundation wall i Interest rate I Effective moment of Inertia ir Rainfall intensity ihg Hydraulic gradient between two points IPD Post-Disaster Inflation k Coefficient of permeability for soils K Scour factor based upon flow angle of attack kp Passive soil pressure coefficient Kp Resistance coefficient of the pipe fitting(s) KS Effective section modulus I Length lbs Pounds lbs/ft3 Pounds per cubic foot LF Linear Feet LL Live Load L. Minimum uniformly distributed live Load M Mass of object max Maximum flood depth considered above zero flood depth Mb Bending Moment Page xxvi T Table of Contents NOMENCLATURE (continued) MDDF Expected damage by flood depth min Minimum damaging flood considered above zero flood depth MO Sum of Overturning Moments MR Sum of Resisting Moments MSL Mean Sea Level n Assumed life of a structure NAVD North American Vertical Datum NFIP National Flood Insurance Program NGVD National Geodetic Vertical Datum NOAA National Oceanic and Atmospheric Administration NPV Net Present Value or benefit of a mitigation measure NRCS Natural Resources Conservation Service NWS National Weather Service P Load Pd Hydrodynamic Pressure due to high velocity flow flood PD Lateral hydrostatic Pressure from saturated soil Pdh Hydrostatic Pressure due to low velocity flood flows Ph Hydrostatic Pressure from standing water psi Pounds per square inch PWF Present Worth Factor q Soil pressure Q Discharge in a given unit of time Page xxvii o Table of Contents NOMENCLATURE (continued) Qa,bc Runoff Quantity (discharge) from a defined area QBC Allowable Bearing Capacity QSP Minimum discharge for sump pump installation QU Ultimate bearing capacity RENT Scenario rental income losses Rr Resistance due to foundation friction RF Flood depth considered above zero flood depth s Slenderness ratio Sa Allowable Soil bearing pressure (capacity) SA Section Area of component Sbc Soil bearing capacity SC Effective (unit) weight of concrete SCD Total Scenario Damages (per event) Sd Potential scour depth SF Square Foot (feet) SFHA Special Flood Hazard Area S2 Unit weight of wall material SL Snow Load Smax Maximum potential depth of scour hole SP Specific gravity of sediment Sq. Mi. Square Mile sr Seepage rate Page xxviii * Table of Contents NOMENCLATURE (continued) SW Self Weight of component t Time of impact TA Total Area occupied (SF) TDC Displacement Costs per day (per SF) tftg Footing thickness TH Total Head TL Total Load TLdjI Total Load due to dead, live, and snow loads TVA Tennessee Valley Authority LI Foundation wall thickness twall Floodwall thickness UCFEMA FEMA Unit Cost at specific location UC1IW Unit Cost for a locality USACE U.S. Army Corps of Engineers USGS United States Geological Survey V Velocity of floodwater VI Volume of concrete required to offset tank buoyancy V8 Shear force V, Volume of tank w Span lengths between walls or wall and girder Wa Total gravity forces WC Width of closure shield Page xxix Table of Contents Wftg Wg Wn Wi WPIFEMA WPIiocai ws Wsh Wst Wt Wu Wwh y NOMENCLATURE (continued) Weight of the footing Total gravity forces per linear foot of wall Weight of object for normal impact loads Weight FEMA Wholesale Price Index for a locality Wholesale Price Index for a locality Weight of object for special impact loads Weight of soil over floodwall heel Weight of soil over floodwall toe Weight of tank Unit weight of component Weight of floodwall Weight of water above floodwall heel Support width factor Page xxx FOREWORD The riverine and coastal floodplains of the United States are among the most highly desirable areas in the nation for habitation and construction. Unfortunately, many of these areas are very susceptible to flooding, which is the single most expensive and persistent natural disaster the country experiences. Flooding causes millions of dollars in property damage each year, despite concentrated efforts of government and the private sector to mitigate flood hazards. The National Flood Insurance Program (NFIP) was created in 1968 by the Congress not only to provide federally-backed flood insurance to those who generally were not able to obtain it from private-sector companies, but also to promote sound floodplain management practices in flood- prone areas. The floodplain management aspects of the program are administered by the Mitigation Directorate and the insurance aspects are administered by the Federal Insurance Administration (FIA), both parts of the Federal Emergency Management Agency (FEMA), under the authority of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973, U.S.C. 4001-4128, as amended. Figure v-: Flooding along major rivers can createwidespreaddamage. One NFIP mission is to work with communities to reduce future flood losses by establishing guidelines for protecting existing and new development in flood-prone areas. The program makes flood insurance coverage available for structures in those communities that adopt and enforce floodplain management ordinances and regulations that meet or exceed the minimum NFIP requirements as provided for in Section 44 of the Code of Federal Regulations (44 CFR). Coverage is available for walled and roofed structures that are principally above ground and not entirely over water, including manufactured homes that are anchored to permanent foundations. Flood insurance is available for all structures in a participating community, whether the structures are located inside or outside the floodplain identified by FEMA. Owners who have experienced flooding know that complete recovery is often impossible. In addition to the time and money spent repairing or replacing damaged items, they must also deal Xxxi with cleaning property, alleviating health risks and safety hazards, losing time from work, find ing alternative housing, and the emotional toll of the experience. Responding to flood events also depletes resources at every level of government. Human resources and capital must be diverted to providing emergency services, rebuilding public facilities, financing individual assistance for uninsured victims, and to other efforts. In the Great Midwest Flood of 1993, for example, FEMA estimated damage costs exceeded $10 billion. Many of the flood insurance claims received by the NFIP are for structures that have previously incurred flood damage. Structures for which two or more claims of more than $1,000 each have been paid during the previous ten-year period are considered to be repetitive loss structures according to the NFIP. Most repetitive loss claims are for small amounts and involve structures built before NFIP-compliant floodplain management regulations were adopted by the community. However, owners have the option of taking steps to reduce the likelihood of serious future flood damage. Retrofitting individual flood-prone structures is a proven technology that has been in use for many years. If a flood-prone structure is substantially damaged, certain criteria established by the NFIP must be met prior to the initiation of any repair activity. Specifically, NFIP regulation 44 CFR 60.3(c)(2) requires communities to ensure that substantially damaged or improved residential structures be elevated so that the lowest floor is at or above the Base Flood Elevation, (BFE), also known as the 100-yearflood level. "Substantially damaged" is defined as damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damaged condition would equal or exceed 50% of the value of the structure before the damage occurred. Given the potential cost of recovering from a serious flood event and meeting the NFIP's criteria for restoring substantially damaged property, the owner of a flood-prone home has an incentive to undertake retrofitting measures to limit future flood damages. FEMA and the other contributing agencies and organizations have developed this manual to provide engineering and related economic guidance to professional designers and local officials about what constitutes technically feasible and cost-effective retrofitting techniques. However, the guidance provided in this manual should be considered generic in nature, subject to final refinement in accordance with local regulations and specific site and structural conditions. It is not intended to be used as a code or specification, nor as a replacement for the engineer's or architect's standard of performance. Through the information and analyses presented in this manual, local officials, and design professionals will gain a better understanding of the advantages of retrofitting and may choose to take steps that could ultimately save the nation millions of dollars each year. Richard T. Moore Associate Director for Mitigation Federal Emergency Management Agency O ACKNOWLEDGEMENT FEMA acknowledges the following agencies and organizations for their contributions to this manual: OF AGRICULTURE| 4 U.S. DEPARTMENT e A _ | w ~~~~~~~~~~~~~~~~~~SOLtl CONSERVATION SERVICE 8 0 DEttV me~~~ r * Brudis & Associates, Inc. e Dewberry & Davis * Flo Engineering, Inc. * French & Associates, Ltd. * National Association of Home Builders, (NAHB), Research Center * National Institute of Building Sciences (NIBS) * Soza & Company, Ltd. xxxiii . METRIFICATION FEMA is committed to the federal government's transition to metric. However, English units remain the standard of practice for residential construction. Therefore this manual has been prepared using English units. However, it is foreseeable that the metric system will be the standard of measurement in this country within the next few years. With this in mind, soft metric conversion's have been provided to promote familiarity with the metric system. A critical component of unit conversion is rounding. Designers should check to ensure that rounding does not exceed allowable tolerances for design or fabrication. Metric Conversion Factors Quantity From English Units To Metric Units Multiply By: Length foot (m) 0.3048 inch (mm) 25.4 Area square foot m2 0.092 acre m2 4047 Volume gallon L 3.7714 cubic foot m3 .0283 Pressure psf Pa 47.8803 psi kPa 6.8947 Power horsepower kW .746 W 746 Weight pounds kg .4535 Flow cfs Ips 28.3 Velocity fps mps 0.3048 CHAPTER I Featuring: How to Use This Manual Methods of Retrofitting General Retrofitting Cautions Retrofitting Process E-1 X INTRODUCTION TO RETROFITTING -INTRODUCTIONTO RETROFITTING L HOW TO USE THIS MANUAL METHODS OF GENERALRETROFITrING I N I _ RETROFITTING t CAUTIONS IGRETROFITTINGPROCESS Goals and Intended Users Elevation Homeowner Motivation Organization of Relocation Parameters of Retrofitting the Manual Dry Floodproofing Determination of Hazards Wet Floodproofing Benefit/Cost Analysis Floodwalls & Levees Design [ Construction IOperation and Maintenance 20/ Chapter I: Introduction to Retrofitting Table of Contents How to Use This Manual ........................................ I -1 Goals and Intended Users ......................................... ! .I -1 Organization of the Manual .I -2 - Methods of Retrofitting .I 4 Elevation .I -6 Elevation on Solid Perimeter Foundation Walls.I -7 Elevation on Open Foundation Systems.I -9 Relocation.................................................................................................................... I-14 Dry Floodproofing. I-17 Wet Floodproofing.I -20 Floodwalls and Levees.I -22 General Retrofitting Cautions.I -26 Retrofitting Process.I -28 Homeowner Motivation .I -28 Parameters of Retrofitting .I -28 Determination of Hazards .I -28 Benefit/CostAnalysis.I -29 Design.I -29 Construction................................................................................................................. I -29 Operation and Maintenance .I -29 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -i January 1995 How to Use This Manual HOW TO USE THIS MANUAL Other flood-related technical resources are available through federal agencies such as FEMA, the U.S. Army Corps of Engineers, and the Natural Resources ConservationService,aswellas state,regional,andlocalagencies. See Appendix C, Glossary of Resources. Thismanualwillprovidevaluable assistanceto the design profes- sional. It is not intendedto be usedas a code or specification, engineer's orarchitect'sstandard of performance. GOALS AND INTENDEDUSERS This manual has been prepared by the Federal Emergency Management Agency with assistance from other agencies and organizations involved in the nationwide effort to assist local governments, engineers, architects, and property owners involved in retrofitting flood-prone residential structures. Its objective is to provide engineering design and economic guidance to engineers, architects, and local code officials about what constitutes technically feasible and cost-effective retrofit ting measures for flood-prone residential structures. The focus ofthis manual is the retrofitting of one-to four-family residences subject to flooding situations without wave action. The manual presents various retrofitting measures that provide both active and passive efforts and employ both wet and dry floodproofing measures. These include elevation ofthe struc ture in place, relocation ofthe structure, construction of barriers (levees and floodwalls), dry floodproofing (sealants, closures, sump pumps, and backflow valves), and wet floodproofing (flood-resistant materials and protection of utilities and con tents). The goal of this manual is to capture state-of-the-art information and present it in an organized manner. To the maximum extent possible, existing data and modem research have been utilized as the cornerstone of this document. Detailed sections covering the evaluation, planning, and design of retrofitting measures are included along with case studies of completed retrofitting efforts. Methods for performing economic analyses of the various alternatives are presented. Pnninpprinn Prinvinles and Practices of Retrofitting Flood-Prone Residential Structures 1-1 January 1995 ChapterI: Introduction to Retrofitting The architect, engineer, or code official must recognize that retrofitting a residential structure influences how that structure reacts to hazards other than those associated with floodwaters. Flood-related hazards such as water-borne ice and debris 6 impact forces, erosion forces, and mudslide impacts, as well as non-flood-related hazards such as earthquake and wind forces, Coastal situations subject to wave shouldbeconsideredintheretrofittingprocess. Retrofittinga action are not addressed in this structure to withstand only floodwater-generated forces may manual. For information on that impair the structure's ability to withstand the multiple hazards area the reader is referred to mentioned above. Thus, it is important to approach the retro oS. Corps of Engineers (USACE) Shore perspective. ProtectionManual. Manual, and the U Atry fitting method selection and design process with a multi-hazard ORGANIZATION OF THE MANUAL This manual has seven chapters and five appendixes. Chapters 1, 11, and III * Introduction to Retrofitting * Regulatory Framework * Parameters of Retrofitting Chapters IV and V * Determination offHazards * Benefit/Cost Analysis and Alternative Selection These chapters give detailed guidance on how to focus on the specific retrofitting solution that is most applicable forthe residential structure being evaluated. I -2 Enqineerinq Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 How to Use This Manual The balance of the design manual encompasses the following: ChapterVI * Design Practices This chapterprovides step-by-stepdesignprocessesfor each retrofitting measure. (Note: Each retrofitting measure has its own tab and is organized as a subchapter.) ChapterVII * Case Studies This chapter is a collection of information on the actual retrofit- ting of specific residential structures. Throughout this manual, the following icons are used, indicating: Special Note: I0 IccC I ccD Formula: Bomb: Significantorinterestinginformation Use of a mathematical formula I Special cautions need to be exercised Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-3 January 1995 Chapter I: Introductionto Retrofitting ~~~~~~L, METHODS OF RETROFITTING Retrofitting involves a combination of adjustments or additions to features of existing structures that are intended to eliminate or reduce the possibility of flood damage. Retrofitting measures includes the following: Elevation: Relocation: Dry Floodproofing: Wet Floodproofing: Floodwalls/Levees: The elevation ofthe existing structure on fill or foundation elements such as solid perimeter walls, piers, posts, columns, or pilings. Relocating the existing structure outside the identified floodplain. Strengthening of existing foundations, floors, and walls to withstand flood forces while making the structure watertight. Making utilities, structurecomponents, and contents flood-and water- resistant during periods of flooding within the structure. The placement of floodwalls or levees around the structure. I -4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 See page I-26 for general cautions to consider in the implementation of a retrofitting measure. Methods of Retrofitting Retrofitting measures can be passive or active in terms of necessaryhuman intervention. Active or emergency retrofitting measures are effective only if there is sufficient warning time to mobilize labor and equipment necessary to implement the measures. Therefore, every effort should be made to design retrofitting measures that are passive and do not require humanintervention. Fnninrigrmnn Prinrinie anndPracticae nf Retrnfiftinn Flood-Prone Residential Structures I -5 January 1 995 Chapter I: 6 Cost is an important factor to consider in elevating structures. As an example, lighter wood-frame structures are easier and often cheaper to raise than masonry structures. Masonry structures are not only more expensive to raise, but are also susceptible to cracks. 'olv Base Flood is defined as the flood having a 1% chance of being equaled or exceeded in any given year. The Base Flood Elevation (BFE) is the elevation to which floodwaters rise during a Base Flood. Introduction to Retrofitting ELEVATION Elevating a structure to prevent floodwaters from reaching damageable portions is an effective retrofitting technique. The structure is raised so that the lowest floor is at or above a designated flood protection elevation (FPE). Heavy-duty jacks are used to lift the existing structure. Cribbing sup ports the structure while a new or extended foundation is constructed below. In lieu of building new support walls, open foundations such as piers, columns, posts, and piles are often used. Elevating a structure on fill is also an option in some situations. While elevation may provide increased protection of a structure from floodwaters, other hazards must be considered before implementing this strategy. Elevated structures may encounter additional wind forces on wall and roof systems, and the existing footings may experience additional loading. Extended and open foundations (piers, piles, posts, and col umns) are also subject to undermining, movement, and impact fahilures caused by seismic activity, erosion, ice or debris flow, mudslide, and alluvial fan forces, among others. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting Elevation on Solid Perimeter Foundation Walls Flood Protection Elevation (FPE), also referred to as the Flood Protection Level (FPL), is the elevation (height) to which a retrofittingmeasureis designed. Typically, the FPE is a function of the expected flood elevation (normally the BFE) plus a minimum freeboard value of 1.0 foot. Elevation on solid perimeter foundation walls is normally used in areas of low to moderate water depth and velocity. After the structure is raised from its current foundation, the support walls can often be extended vertically using materials such as masonry block or cast-in-place concrete. The structure is then set down on the extended walls. While this may seem to be the easiest solution to the problem of flooding, there are several imotncnsdrin. important considerations. Depending on the structure and potential environmental loads (such as flood, wind, seismic, and snow), new, larger footings may have to be constructed. It may be necessary to reinforce both the footings and the walls using steel reinforcing bars to provide needed structural stability. Deep floodwaters can generate loads great enough to collapse the structure regardless of the materials used. Constructing solid foundation walls with openings or vents will help alleviate the danger by allowing hydrostatic forces to be equalized on both sides. For new and substantially damaged or improved buildings, openings are required under the NFIP. Elevation Utilities and electrical circuits moved above flood level Lightweight or mobile items; ca be strender the house and moved prior to flooding 1R ' e1_ :.... Openings on each wall ensure entry of a."" : :,.water to equalize hydrostatic pressures Figure I-1: Elevation on Solid Perimeter Foundation Walls Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -7 January 1995 Chapter I: Introduction to Retrofitting Fgr1-:M7ioofEitn eiconEtneFonainWl Figure 1-2: Elevation of Existing Residence on Extended Foundation Walls Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Figure 1-3: Elevation on Piers Methods of Retrofitting Elevation on Open Foundation Systems Open foundation systems are vertical structural members that support the structure at key points without the support of a continuous foundation wall. Open foundation systems include piers, posts, columns, and piles. ELEVATION ON PIERS The most common example of an open foundation is piers, which are vertical structural members that are supported entirely by reinforced concrete footings. Despite their popularity in construction, piers are often the elevation technique least suited for withstanding significant horizontal flood forces. In conventional use, piers are designed primarily for vertical loading; when exposed to flooding, they may also experience horizontal loads due to moving floodwater or debris impact forces. Other environmental loads, such as seismic loads, can also create significant horizontal force. For this reason, piers used in retrofitting must not only be substantial enough to support the vertical load ofthe structure, but also must be sufficient to resist a range of horizontal forces that may occur. Piers are generally used in shallow depth flooding conditions with low-velocity ice, debris, and water flow potential, and are normally constructed of either masonry block or cast-in-place concrete. In either case, steel reinforcing should be used for both the pier and its support footing. The reinforced elements should be tied together to prevent separation. There must also be suitable connections between the superstructure and piers to resist seismic, wind, and buoyancy forces. Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures I -9 January 1995 Chapter I: Introduction to Retrofitting ELEVATION ON POSTS OR COLUMNS Elevation on posts or columns is frequently used when flood -E H1- conditions involve moderate depths and velocities. Made of wood, steel, or precast reinforced concrete, posts are generally square-shaped to permit easy attachment to the house structure. However, round posts may also be used. Set in pre-dug holes, posts are usually anchored or embedded in concrete pads to handle substantial loading requirements. Concrete, earth, gravel, a Poet or crushed stone is usually backfllled into the hole and around the base of the post. Reinfonce Concrete FootingrWhile piers are designed to act as individual support units, posts Figure 1-4: Elevation on Posts nomnally must be braced. There are a variety ofbracing techniques such as wood knee and cross bracing, steel rods, and guy wires. Cost, local flood conditions, loads, the availability of building materials, and local construction practices fiequently influence which technique is used. Columns differ from posts in the size of their application. Posts are small columns. ..~~~~~~~ Figure 1-5: Structure Elevated on Posts I- 10 Enaineerina Princioles and Practices of Retrofittina Flood-Prona Raeidantial Struicrean -I -vo r h.._ ..__Jnr9I January 1 995 Figure 1-6: Elevation on Piles Methods of Retrofitting ELEVATION ON PILES Piles differ from posts in that they are generally driven, orjetted, deeper into the ground. As such, they are less susceptible to the effects of high-velocity floodwaters, scouring, and debris impact. Piles must either rest on a support layer, such as bedrock, or be driven deep enough to create enough friction to transfer anticipated loads to the surrounding soil. Piles are often made of wood, although steel and reinforced precast or prestressed concrete are also common in some areas. Similar to posts, they may also require bracing. Because driving piles generally requires bulky, heavy construction machinery, an existing house must normally be moved aside and set on cribbing until the operation is complete. The additional cost and space needs often preclude the use of piles in areas where alternative elevation methods for retrofitting are technically feasible. Several innovative methods have been developed for setting piles. These include jetting exteriorpiles in at an angle using high-pressure water flow, and trenching, or auguring, holes for interior pile placement. Augured piles utilize a concrete footing for anchoring instead of friction forces. This measure requires that the existing home be raised several feet above its final elevation to allow room for workers to install the piles. Fnnineerinn Princinles and Practice s of Retrofittino Flood-Prone Residential Structures I -11 January 1995 Chapter I: Introduction to Retrofitting LL.5,~~~~~ MD..A 3.,A. P jdli.. .1.._ Figure 1-7: Structure Elevated on Piles Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting Tablel-I Advantages and Disadvantages of Elevation Advantage. I * Ifelevated to the BFE, allows for a substantially damaged or Improved structure to be brought Into complIance with the NFIP * Reduces flood risk to the structure and its contents * Eliminates the need to relocate vulnerable items above the flood level in the house during conditions of flooding * Often reduces flood insurance premiums * Techniques are well-known and qualified contractors are often readilyavailable * Reduces the physical, financial, and emotional strain that accompanies flood events * Does not require the additional land that may be needed for floodwalls or levees Dlsadvantages * Cost may be prohibitive * The appearance of the structure may be adversely affected * The structure should not be occupied during a flood * Access to the structure may be adversely affected * Not appropriate in areas with high- velocity water flow, fast-moving ice or debris flow, or erosion unless special measures are taken * Additional costs may be incurred to bring the structure up to current building codes for plumbing, electrical, and energy systems * Forces due to wind and seismic hazards must be considered Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-13 January 1995 Chapter I: Introduction to Retrofitting RELOCATION Another retrofitting method is to move the structure to a location that is less prone to flooding and flood-related hazards such as erosion. This method is commonly referred to in retrofitting literature as relocation. The structure may be relocated to another portion of the current site or to a different site. The surest way to eliminate flood damage to a structure is to remove it from the floodplain and relocate it to a flood-free location. The procedure normally involves placing the structure on a wheeled vehicle. The structure is then transported to a new location and set on a new foundation. Relocation is an appropriate measure in high hazard areas where continued occupancy is unsafe and/or owners want to be free from flood worries. It is also a viable option in communities that are considering using the resulting open space for more appropriate floodplain activities. Relocation may offer an alternative to elevation for substantially damaged structures that are required under local regulations to meet NFIP requirements. .I---1. __ -. -I . Figure 1-8: Structure Placed on a Wheeled Vehicle for Relocation to a New Site 1-14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting While similar to elevation, relocation of a structure requires additional steps that normally increase the cost ofthis retrofitting method. These additional costs include moving the structure, purchase and preparation of a new site to receive thestructure (with utilities), construction ofanew foundation, and restoration ofthe old site. Mosttypes and sizes of structures can be relocated either as a unit or in segments. One-story wood-frame houses are usually the easiest to move, particularly if they are located over a crawl space or basement that provides easy access to floor joists. Smaller, lighter wood-frame structures may also be lifted with ordinary house-moving equipment and often can be moved without partitioning. Houses constructed of brick, concrete, or masonry are also movable, but usually with more difficulty and increased costs. Structural relocation professionals should help owners to consider many factors in the decision to relocate. The structural soundness should be thoroughly checked and arrangements should be made for temporary housing and storage of belongings. Many states and communities have requirements governing the movement of structures in public rights-of-way. Figure I-9: Structure to be Relocated Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I-15 January 1995 Chapter I: Introduction to Retrofitting I Table 1-2 Advantages and Disadvantages of Relocation Advantages Disadvantages * Allows for substantially damaged * Cost may be prohibitive or Improved structure to be brought Into compliance with the NFIP * A new site must be located * Significantly reduces flood risk to the * Dispositionof the flood-prone lot structure and its contents must be addressed * Relocationtechniques are well-known * Additional costs may be incurred to and qualified contractors are often bring the structure up to current readilyavailable building codes for plumbing, electri cal, and energy systems * Can eliminate the need to purchase flood insurance or reduce the premium * Reduces the physical, financial, and emotional strain that accompanies flood events Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting DRYFLOODPROOFING Anotherapproachto retrofittingis to seal thatportion of a structure below the flood protection level, making that area watertight. The objective of this approach is to make the walls and other exterior components impermeable to the passage of floodwaters. Creating an impervious membrane, such sealant systems can include wall coatings, waterproofing compounds, impermeable sheeting, or supplemental impermeable wall systems, such as cast-in-place concrete. Doors, windows, sewer and water lines, and vents are closed with permanent or removable shields or valves. The expected duration of flooding is extremely critical when using sealing systems because seepage can increase overtime, Dry floodproofing is not allowed rendering the floodproofing ineffective. Waterproofing comunder the NFIP for new and pounds, sheeting, or sheathing may fail or deteriorate if exposed substantially damaged or improved residential structures to floodwaters for extended periods. Sealant systems are also located in a Special Flood Hazard subject to damage (puncture) in areas that experience water Area. Additional information on flow ofsignificant velocity, or ice or debris flow. dry floodproofing can be obtained from FEMA Technical Bulletin 3-Dry floodproofing is usually appropriate only where floodwaters 93, entitled Non-Residential Floodproofing Requirements and are less than three feet deep, since most walls and floors in Certification for Buildings residential structures may collapse or buckle under higher water Located in Special Flood Hazard levels. Research in this area has been conducted by the U.S. Areas in Accordance with the .N-snathq Army Corps of Engineers and is available in a document entitled are also applicable in residential Floodproofing Tests, August 1988. situations. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -17 January 1995 Chapter I: Introduction to Retrofitting ~~~~~~~~~~~~~~~~~~~~~~~~Ls Backflowvalve i Account for sewer and drain backup Figure I-10: Dry Floodproofed Structure Dry floodproofing is also not recommended for structures with a basement. Thesetypes of structurescan be susceptible to significant lateral and uplit, or buoyancy, forces. When dry Even brick or concrete block walls should not be floodproofed above a height of three feet (without an extensive engineering analysis) floodproofing awood-frame superstructure, only buildings constructedof concrete block or faced with brick veneer should be considered. Weaker construction materials, such as wood-frame superstructure with siding, will often fail at much due to the danger of structural lower water depths from hydrostatic forces. failure from excessive hydrostatic and other flood-related forces. The designer should consider incorporating freeboard into the three-foot height constraint as a factor of safety against structural failure. Other factors of safety might include additional pumping capacity and stiffened walls. I-18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting TableI-3 Advantages and Disadvantages of Dry Floodproofing Advantages * Reduces the flood risk to the structure and contents if the design flood level is not exceeded * May be less costly than other retrofitting measures * Does not require the extra land that may be needed for floodwalls or levees * Reduces the physical, financial, and emotional strain that accompanies flood events * Retains the structure in its present environment and may avoid significant changes in appearance Disadvantages * Does not satisfy the NFIP requirement for bringing substantially damaged or Improved residential structures Into compliance * Requiresongoing maintenance * Flood insurance premiums are not reducedfor residential structures * Usually requireshuman intervention and adequate warning time for installation of protective measures * Measures can fail or be exceeded by large floods, in which case the effect will be as if there were no protection at all * If design loads are exceeded, walls may collapse, floors may buckle, and the structure may even float, potentially resulting in more damage than just letting the house flood * The structure should not be occupied during a flood * Shields are not always aesthetically pleasing * The damage to the exterior of the structure and other property may not be reduced * May be subject to leakage, which could cause damage to the structure and its contents Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -19 January 1995 n-c \Chapter I: Introduction to Retrofitting L A WETFLOODPROOFING Another approach to retrofitting involves moding a structure to allowfloodwatersto enter itin away thatwillminimize damagetothe structureand itscontents. This typeof protec tion is classified as wet floodproofing. Wet floodproofing is often used when all other techniques are not technically feasible or are too costly. It is generally appropriate if a structure has available space in which to relocate and temporarily store damageable items. Utilities and firnaces may also needto be relocatedor protectedalongwith othernon- movable items by using flood-resistant building materials. Wet floodproofing may also be appropriate for structures with basementsand crawlspacesthat cannotbe protectedtechni- Wetfloodprooflngisnotallowed cally or cost-effectively by other retrofitting measures. under the NFIP for new and substantiallydamagedor im- Compared with the more extensive flood protection measures provedstructureslocatedin a described in this manual, wet floodproofing is generally the least SpecialFlood Hazard Area. Refer . The majorcosts ofthis measure involve the rear- to FEMA's Technical Bulletin #7 93, entitled Wet Floodproofing rangement ofutility systems, installation of flood-resistant Requirements for Structures materials, acquisition of labor and equipment to move items, Located in Special Flood Hazard and organization of cleanup when floodwaters recede. Major Areas in Accordance with the disruptions to structure occupancy often result during conditions .~l? of flooding. Wet Floodproofing Openingsprovided Lowestfloor to~letwaterin =o Furnaceandutilities ' I relocated are _. s Largeappliancesaremoved orwrappedinwaterproofbags Figure I- 1: Wet Floodproofed Structure I-20 Enoineerino Princioles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting Table i-4 Advantages and Disadvantages of Wet Floodproofing Advantages * No matter how small the effort, wet floodproofing can, in many instances, reduce flood damageto a building and its contents * Compared to a dry floodproofing measure, loads placed on the walls and floors of a building may be greatly reduced due to equalized hydrostatic pressure * Costs for relocating or storing contents (except basement contents) after a flood warning is issued are covered by flood insurance under certain conditions * Wet floodproofing measuresare often less costly than other measures * Does not require extra land, which may be needed for floodwalls or levees * Reduces the physical, financial, and emotional strain that accompanies flood events Disadvantages * Does not satisfy the NFIP requirement for bringing substantially damaged or Improved structures Into compliance * Flood warning is usually needed to prepare the building and contents for flooding * The evacuation of contents from the flood-prone area is dependent on human intervention * The structure will get wet inside, and possibly be contaminated by sewage, chemicals, and other materials borne by floodwaters. Extensive cleanup may be necessary * The structure should not be occupied during a flood * The structure may be uninhabitable for a time after flooding * There may be a need to limit the uses of the floodable area of the building * There may be some ongoing maintenance requirements * Additional costs may be incurred to bring the structure up to current building codes for plumbing, electrical, and energy systems * To avoid foundation wall collapse, care must be taken when pumping out basements Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -21 January 1995 Chapter I: Introduction to Retrofitting FLOODWALLS AND LEVEES Another retrofitting approach is the construction of localized barriers between the structure and the source offlooding. There are two basic types of barriers: levees and floodwalls. They can be built to any height but are usually limited to four feet for floodwalls and six feet for levees due to cost, aesthetics, access, water pressure, and space. Local zoning and building codes may also restrict use, size, and location. A levee is typically a compacted earthen structure thatblocks floodwaters from coming into contact with the structure. To be effective over time, levees must be constructed of suitable materials (i.e., impervious soils) and with correct side slopes for stability. Levees may completely surround the structure or tie to high ground at each end. Levees are generally limited to homes where floodwaters are less than five feet deep. Otherwise, the 0 cost and the land area required for such barriers usually make 46 them impractical for the average owner. Floodwalls and levees are not allowed under the NFIP for new Floodwalls are engineered barriers designed to keep floodwa- and substantially damaged or ters from coming into contact with the structure. Floodwalls improved structures located in a SpecialFlood Hazard Area. can be constructed in a wide variety of shapes and sizes but are typically built of reinforced concrete and/or masonry materials. Floodwalls and Levees r Floodwall is reinforced Levee is compacted andanchoredto withstand fill with 2:1 or 3:1 slope_ __ _ hydrostatic E i,] load E_ _ _ f _ forsewer I and drain backupSumpand pump handleseepage . | ~~~Account and internaldrainage Bowvalve FigureI-12: StructureProtectedbyLevee and Floodwall I-22 Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures January 1995 Methods of Retrofitting Figure 1-13: House Protected by a Floodwall Generally, residential floodwalls are only cost-beneficial at providing protection up to four feet and levees up to six feet, including one foot of freeboard. A floodwall can surround an entire structure or, depending on the flood levels, site topography, and design preferences, it can protect isolated structure openings such as doors, windows, or basement entrances. Floodwalls can be designed as attractive features to a residence, utilizing decorative bricks or blocks, landscaping, and garden areas, or they can be designed for utility at a considerable savings in cost. Because their cost is usually greater than that of levees, floodwalls would normally be considered only on sites that are too small to have room for levees or where flood velocities may erode earthen levees. Some owners may believe that floodwalls are more aesthetically pleasing and allow preservation of site features, such as trees. Special design considerations must be taken into account when floodwalls or levees are used to protect homes with basements because they are susceptible to seepage that can result in hydrostatic and saturated soil pressure on foundation elements. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -23 January 1995 Chapter I: Introduction to Retrofitting i k The costs of floodwalls and levees can vary greatly, depending on height, length, availability of construction materials, labor, access closures, and the interior drainage system. A levee Provisions for closing access openings must be included as part could be constructed at a lower cost if the proper fill material is available nearby. of the floodwall or levee design. Figure 1-14: House Protected by a Levee I -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Methods of Retrofitting Table I-5 Advantages and Disadvantages of Floodwalls and Levees Advantages [ Disadvantages * The area around the structure will be protected from inundation without significant changes to the structure * There is no pressure from floodwater to cause structural damage to the home or other structures in the protected area * These barriers are usually less expensive to build than elevating or relocating the structure would be * Occupants do not have to leave the structure during construction * Reduces flood risk to the structure and its contents * Reduces the physical, financial, and emotional strain that accompanies flood events * Does not satisfy the NFIP requirements for bringing substantially damaged or Improved structures Into compliance * Levees and floodwalis can fail or be overtopped by large floods or floods of long duration, in which case the effect will be as if there were no protection at all * May be expensive * Both floodwalis and levees need periodicmaintenance * Interior drainage must be provided * Local drainage can be affected, possibly resulting in water problems for others * No reduction in flood insurance rates * May restrict access to structure * Levees require considerable land area * Floodwalls and levees do not eliminate the need to evacuate during floods * May require warning time and human intervention for closures * Floodplain management requirements may make floodwalls and levees violations of applicable codes and/or regulations Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -25 January 1995 ChapterI: Introductionto Retrofitting GENERAL RETROFITTING CAUTIONS Appropriately applied retrofitting measures have several advan tages over other damage reduction methods. Individual owners can undertake retrofitting projects without waiting for govern ment action to construct flood control projects. Retrofitting may also provide protection in areas where large structural projects, such as dams or major waterway improvements, are not feasible, warranted, or appropriate. Some general cautions should always be considered in implementing a retrofitting strategy. These include: * Substantial damage or improvement requirements under the NFIP, local building codes, and floodplain management ordinances render some retrofitting measures illegal. * Codes, ordinances, and regulations for other restrictions, such as setbacks and wetlands, should be observed. * Retrofitted structures should not be used nor occupied during conditions of flooding. * Most retrofitting measures should be designed and constructed by experienced professionals (engineers, architects, or contractors) to ensure proper consideration of all factors influencing effectiveness. * Most retrofitting measures cannot be installed and forgotten. Maintenance must be performed on a scheduled basis to ensure that the retrofitting measures adequately protect the structure over time. * Floods may exceed the level of protection provided in retrofitting measures. In additionto implementing these protective measures, owners should consider continuing- and may be required-to purchase flood insurance. In some cases, owners may be required by lending institutions to continue flood insurance coverage. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 General Retrofitting Cautions * When human intervention is most often needed for successful flood protection, a plan of action must be in place and an awareness of flood conditions is required. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter I: Introduction to Retrofitting RETROFITTING PROCESS A good retrofitting project should follow a careful pat of exploration, fact finding, analysis, detailed design, and construction steps. The successful completion of a retrofitting project will require a series of homeowner coordination and design input meetings. Ultimately, the homeowner will be living with the retrofitting measure, so every effort should be made to incorporate the homeowner's concerns and preferences into the final product. The primary steps in the overall process are shown in Figure I-15 and include: HOMEOWNER MOTIVATION The decision to consider retrofitting options usually stems from having experienced or witnessed a flooding event in or near the structure in question; having experienced substantial damage from a flood or an event other than a flood; or embarking on a substantial improvement, whichrequires adherence to local floodplain regulations. The homeowner may contact other homeowners, community officials, contractors, or design professionals to obtain information on retrofitting techniques, available technical and financial assistance, and other possible options. PARAMETERS OF RETROFITTING The goal ofthis step is to conduct the necessary field investiga tions, regulatory reviews, and preliminary technical evaluations to select applicable and technically feasible retrofitting tech niques that warrant further analysis. DETERMINATIONOF HAZARDS This step involves the detailed analysis of flood, flood-related, and non-flood-related hazards and the evaluation of specific sites and structures to be retrofitted. I-28 EngineeringPrinciplesand Practices of Retrofitting Flood-Prone Residential Structures January 1995 Within each of these steps, homeowners are involved in providing input into the evaluations, analyses, decisions, and design concepts to ensure that the final product meets their requirements. Finally, maintenance of the constructed retrofitting measure is the responsibility of the homeowner. Retrofitting Process BENEFIT/COST ANALYSIS This step is critical in the overall ranking of technically feasible retrofitting techniques, and it combines an objective economic analysis of each retrofitting measure considered with any subjective decision factors introduced by the homeowner or others. DESIGN During this phase, specific retrofitting measures are designed, construction details developed, cost estimates prepared, and construction permits obtained. CONSTRUCTION Upon final design approvals, a contractor is selected and the retrofitting measure is constructed. OPERATION AND MAINTENANCE The development of a well-conceived operation and maintenance plan is critical to the overall success of the project. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures I -29 January 1995 Chapter I: Introduction to Retrofitting I I --Homeowner Motivation 0~~ Hoeone Coordination -' Parameters of Retrofitting ; tf Determination of Hazards {i| Benefit Cost Analysis 7 NL=W Design jjl-Construction .I 7 -, '----N: -i -.U:e-v '" ... :-.:c I Figure I-15: Primary Steps in the Retrofitting Process I -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 * C HAPTERII i} Alan ',N -" I I REGULATORYFRAMEWORK Featuring: National FloodInsurance Program (NFIP) CommunityRegulationsand the Permitting Process Model Building Codes Code Compatibility with the NFIP (000" k II NATIONAL FLOOD INSURANCE PROGRAM (NFIP) I COMMUNITY REGULATIONS AND THE PERMITTING PROCESS MODEL BUILDING CODES I CODE COMPATIBILITY WITH THE NFIP Flood Hazard Information * Building Officials and Code Administrators (BOCA) Floodplain Management Regulations * Southern Building Code Congress Intemational Insurance Program (SBCCI) * International Council of NFIP Flood-Prone Building Code Officials (ICBO) Building Performance Standards * Council of American Building Officials (CABO) * National Fire Protection Association (NFPA) IK -_WS , mu , _ = )1 Chapter II: Regulatory Framework Table of Contents National Flood Insurance Program (NFIP) .......................................... II -2 Flood Hazard Information .......................................... II -4 RiverineFloodplains.......................................... II -4 Coastal Floodplains ........................................... II -8 ZoneDefinitions.......................................... II-11 ........ L 3.................... FloodplainManagementRegulations II-13 Insurance Program ........................................... II --16 Pre-FIRM Versus Post-FIRM (Insurance Purposes) ........................................... II -17 NFIP Flood-Prone Building Performance Standards ..................................... , IL-18 * Community Regulations and the Permitting Process ..................................... II -19 Model Building Codes ..................................... II -21 CodeCompatibilitywiththeNFIP ..................................... II -23 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures 11. Inni mrvs 1Qq!r! I REGULATORY FRAMEWORK Most retrofitting projects are regulated by local floodplain, zoning, and building code ordinances. In addition to governing the extent and type of activities allowable in the regulatory floodplain, these codes set construction standardsthat must be met both by newconstructionand by substantial improvement and repair of damaged buildings. The portions of these ordinances dealing with retrofitting are generally derived from guidance issued by FEMA under the NFIP and the U.S. Army CorpsofEngineers (USACE). This chapter discusses thetypical community floodplain management and building code environment, including: * the role of local officials in a retrofitting project, * the various tenets of theNFIP, and * the compatibility of items covered in model building codes withtheNFIP. Each jurisdiction may adopt standards that are more restrictive than the minimum NFIP requirements, but this sectionwill examine only the minimum federal regulations governing construction in a Special Flood Hazard Area. Local building codes and construction standards vary widely across the country. L In individual communities, local regulations are the mechanism by which NFIP requirements are enforced. The reader is encour aged to contact local floodplain management and building code officialsto determine ifmore restrictive requirements are in place. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ,~~~~~I 1-1 January 1995 Chapter II: Regulatory Framework NATIONAL FLOOD INSURANCE PROGRAM (NFIP) The creation ofthe National Flood Insurance Program was a major step in the evolution of floodplain management. During the 1 960s, Congress became concerned with problems relatedto the traditional methods of dealing with flood damage. It concluded: * Flood protection structures are expensive and cannot protect everyone. * People are still building in floodplains and therefore are risking disaster. * Disaster relief is inadequate and expensive. * The private insurance industry cannot sell affordable flood insurance because only those at significant risk will buy it. * Federal flood control programs are funded by all taxpayers, but they primarily help only those who live in the floodplains. In 1968,Congresspassed theNational Flood Insurance Act to correct some ofthe shortcomings ofthe traditional flood control and flood reliefprograms. The Act created the National Flood Insurance Program (NFIP) to: * Guide future development away from flood hazard areas; * Require that new and substantially improved buildings be constructed to resist flood damage; * Provide floodplain residents and owners with financial assistance after floods, especially after smaller floods that donot warrant federaldisasteraid; and * Transfer some of the costs of flood losses from the taxpayers to floodplain property owners through flood insurance premiums. Enainearina Princinlas and Practices of RPstrnfittint, Flodnr-Pronsa PRsiantial Stritire- January 1995 National Flood Insurance Program (NFIP) Congressoriginallycharged the Departmentof Housing and Urban Development's (HUD's) Federal Insurance Administration (FIA) with responsibility for the program. In 1979, the FIA and the NFIP were transferred to the newly created Federal Emergency Management Agency (FEMA). Currently, the floodplain management aspects ofthe program are administered by the Mitigation Directorate and the insurance aspects are administered by the Federal Insurance Administration, both parts of FEMA. =nminagrinn PrinnirIae anrd Prantirp S nf.Rptrnfittinn Flood-Prone Residential Structures HI-3 _ ,W~fi,.vs Ja hymnuarv ., .my1995, -, , . -____.............. . .. January 1995 Chapter II: Regulatory Framework L w Jg| FLOOD HAZARD INFORMATION Communities that participate in the NFIP's Regular Program typically have a detailed Flood Insurance Study (FIS), which presents flood elevations of varying intensity, including the base V, (100-year) flood, areas inundated by the various magnitudes of FEMA has developed a home flooding, and floodway boundaries. Thisinformation is pre- study course on how to use a sented on a Flood Insurance Rate Map (FIRM) and on a Flood InsuranceStudy (FIS). Flood Boundaryand FloodwayMap (FBFM). Contact your local FEMA regional office (telephone numbers listed in Appendix C)for furtherinforma-Riverine Floodplains tion. The FIS report for riverine floodplains describes in detail how the flood hazard information-including floodways, discharges, velocities, and flood profiles for major riverine areas-was developed for each community. The area ofthe 100-year riverine floodplain is often divided into a floodway and a floodway fringe. The floodway is the channel of a watercourse plus any adjacent floodplain areas that must be kept free of encroachment so that the cumulative effect of the proposed encroachment, when combined with all other existing or proposed encroachments, will not increase the 100year flood elevation more than one foot at any point within the community. The area between the floodway and 1 00-year floodplain boundaries is termed the floodway fringe. The floodway fringe encompasses the portion of the floodplain that could be com pletely obstructed without increasing the water-surface elevation of the 1 00-year flood by more than one foot at any point. Many states and communities limit the allowable increase to lessthan one foot. Enoinesrinn Prinnin~ls and Practicepq nf RPtrnfittinn Flonrd-PrnenPnirantin .QI ttri ti+ra. --a a s 1 -Ie a m --*1 I I ---I1995 J n a -L CD0) 110 CL CD _. C 105 0cC) CD CD 7.5 7.6 7.7 7.8 7.9 8.0 Stream Distance in Thousands of Feet above Confluence with Overpeck Creek .1 z 5. In 0 0 0. 5. CA 0) SD O 0 I0 Q Z1 M 3 I ChapterII: Regulatory Framework Coastal Floodplains In coastal communities that contain both riverine and coastal floodplains, the FIS may contain information on both coastal and riverine hazards. These analyses include the determination ofthe storm surge stillwater elevations forthe 10-, 50-, 100-. and 500- year floods as shown in Table 11-2. Tablell-2 Typical Summary of Coastal Stillwater Elevations Elevation (feet) Above NGVD Floodina Source and Location 10-Yr 50-Yr 100-Yr 500-Yr ATLANTIC OCEAN Entire shoreline within Floodport 8.2 8.9 9.2 9.8 MERRIMACK RIVER Entire shoreline within Floodport 59 7.2 8.2 8.9 These stillwaterelevationsrepresentthepotential flood eleva tions from tropical storms (hurricanes and typhoons), extra tropical storms (northeasters), tsunamis, or a combination of any ofthese events. The FIS wave analysis includes an estimate of the expected beach and dune erosion during the 1 00-year flood and the increased flood hazards from wave heights and wave runup. The increases from wave heights and runup are added to the stillwater elevations to yield the regulatory base flood elevation. This manual doesnotcover Figure II-3illustrates the typical wave height transect showing design issues in CoastalHigh the effects of physical features on thewave heights and corre- Hazard Areas (V Zones). sponding base flood elevation. 11-8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 National Flood Insurance Program (NFIP) V ZONE _ A ZONE WAVE HEIGHT GREATERTHAN3IT. iEW lHEIGHTLETo THU 3T. 00tE 0_~ CR 0rra II I I I i 1 g ! ! ! ! v"mm "M-_ Figure 11-3: Typical Wave Height Transect A FIRM generally shows areas inundated during a 1 00-year flood as either A Zones or V Zones. An example of a FIRM for riverine flooding is shown in Figure 11-4, while a FIRM for coastal flooding is shown in Figure II-5. Retrofitting designers may use data from FIS materials to determine floodplain limits, flood depth, flood elevation, and flood frequency. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 11-9 January 1995 Chapter II: Regulatory Framework Figure 11-4:Typical FIRM for Riverine Flooding ZONE AE (EL 7) Figure 11-5: Typical FIRM for Coastal Flooding Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 National Flood Insurance Program (NFIP) FEMA is in the process of converting from use of the National Geodetic Vertical Datum (NGVD) to the North American Vertical Datum (NAVD). Both datum references will be in use until the transition is completed. Zone Definitions A Zones: are the Special Flood Hazard Areas (except coastal V Zones) shown on a community's FIRM. There are six types of A Zones: A SFHA where no base flood elevation is provided. A#: (Numbered A Zones; e.g., A7 or A14) SFHA where the FIRM shows a base flood elevation in relation to National Geodetic Vertical Datum (NGVD) or North American Vertical Datum (NAVD). AE: SFHA where base flood elevations are provided. AE Zone delineationsare used on newFIRMs instead of A# Zones. AO: SFHA with sheet flow, ponding, or shallow flooding. Base flood depths (feet above grade) are provided. AH: Shallow flooding SFHA. Base flood elevations in relation to NGVD or NAVD are provided. AR Area of special flood hazard that results from the decertification of a previously accredited flood protection system that is determined to be in the process of being restoredto provide a 1 00-year or greater level of flood protection. B Zones: Areas of moderate flood hazard, usually depicted onFIRMs as betweenthe limits of the base and 500-yearfloods. B Zones are also used to designate base floodplains of little hazard, such as those with average depths of less than one foot. Pnninaarinn Prinninip and Practircs of Ratrofittina Flood-Prone Residential Structures II -11 January 1995 Chapter II: Regulatory Framework C Zones: Areas of minimal flood hazard, usually depicted on FIRMs as above the 500-year flood level. B and C Zones may have flooding that does not meet the criteria to be mapped as a Special Flood Hazard Area, such as ponding and local drainage problems. D Zones: Areas of undetermined but possible flood hazard. V Zones: Special Flood Hazard Areas subject to coastal high hazard flooding. There are three types of V Zones, which correspond to the A Zone designations: V: SFHA where no base flood elevation is provided. V#: (Numbered V Zones; e.g.,V7 orV14) SFHA where the FIRM shows a base flood elevation in relation to NGVD orNAVD. 0 YE: SFHA where base flood elevations are provided. VE Zone delineations are now used on new FIRMs instead of V# Zones. XZones: appear on newer FIRMs and incorporate areas previously shown as B and C Zones. 11- 12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 National Flood Insurance Program (NFIP) FLOODPLAINMANAGEMENT REGULATIONS The floodplain management aspects of the NFIP are implemented by communities. A "community" is a governmental body with the statutory authority to enact and enforce development regulations. The authority of each unit of government varies by state. Eligible communities can include cities, villages, towns, townships, counties, parishes, states, and Indian tribes. In 1994, more than 18,350 communities participated in theNFIP. To participate in the NFIP, communities must, at a minimum, regulate development in their floodplains in accordance with the NFIP criteria and state regulations. To do this, communities must require a permit before any development proceeds in the regulatory floodplain. Before the permit is issued, the community must ensure that two basic criteria are met: * All new buildings and substantial improvements to existing buildings will be protected from damage by the base flood, and * New floodplain development will not aggravate existing flood problems or increase damage to other properties. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures It -13 January1995 Chapter II: Regulatory Framework Several definitions are needed to guide the designer through floodplain management regulations. The NFIP definition of key terms is provided below: Structure: For floodplain management purposes, a walled and roofed building, including a gas or liquid storage tank that is principally above ground, as well as a manufactured home. Basement: Any area ofthe structure having its floor subgrade (below ground level) on all sides. Lowest Floor: The lowest floor ofthe lowest enclosed area (including basement). An unfinished or flood- resistant enclosure, usable solely for parking, building access, or storage in an area other than a basement is not considered a building's lowest floor, provided that such enclosure is not built so as to render the structure in violation of the applicable non-elevation design requirement of 44 Code of Federal Regulations (CFR) Ch. 1 (60.3). Enclosed Area Below BFE: An unfinished or flood-resistant enclosure, usable solely for parking, building access, or storage in an area other than a basement that has an elevation below the BFE. Substantial Damage: Damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damaged condition would equal or exceed 50 percent ofthe value of the structure before the damage occurred. Substantial Improvement: Any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50 percent of the value of the structure before the "start of construction" ofthe improvement. This term includes structures that have incurred "substantial damage," regardless of the actual repair work performed. The term does not, however, include either: II -14 Enaineerina Principles and Practices of Retrofitting Flood-ProneResidential Structures January 1995 adA The definitions of pre-FIRM and post-FIRM are different for insurance and floodplain management purposes. National Flood Insurance Program (NFIP) 1. any project to correct existing violations of state or local health, sanitary, or safety code specifications that have been previously identified by the local code enforcement official and that are the minimum necessary to assure safe living conditions, or 2. any alteration of a "historic structure," provided that the alteration will not preclude the structure's continued designation as a"historic structure." Pre FIRM: A pre-FIRM building (for floodplain management purposes) is a building for which the start of construction occurred before the effective date of the community's NFIP-compliant floodplain manage mentordinance. Post-FIRM:Apost-FIRM building (for floodplain management purposes) is a building for which thestart of construction post-dates the effective date ofthe community's NFIP-compliant floodplain management ordinance. Under NFIP criteria, all new (post-FIRM) and substantially damaged/substantially improved construction of residential structureslocatedwithinZones Al -A30, AE, and AH must have the lowest floor at or above the BFE. Therefore, elevation and relocation are the retrofitting alternatives that enable a post- FIRM or substantially damaged/substantially improved structure to be brought into compliance with the NFIP. Utilizing the aforementioned definitions and local codes, the designer can begin to determine which retrofitting measures may be acceptable for each specific home. Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures II -15 January 1995 Chapter II: Regulatory Framework INSURANCE PROGRAM Federally-backed flood insurance is made available in communities that agree to implement NFIP-compliant floodplain management programs that regulate future floodplain development. Communities apply to participate in the program in order to make flood insurance and certain forms of federal disaster assistance available intheir community. Everyone in a participating community can purchase flood insurance coverage, even for properties not located in mapped floodplains. Insurance provides relief for all floods, including those that are not big enough to warrant federal disaster aid, as long as a general condition of flooding exists. The federal government makes flood insurance available only in communities that adopt and enforce floodplain management regulations that meet or exceed NFIP criteria. Because the communities will ensure that future development will be resistant to flood damage, the federal government is willing to support insurance and help make it affordable. The Flood Disaster Protection Act of 1973 expanded the program to require flood insurance coverage as a condition of federal aid or loans from federally-insured banks and savings and loans for buildings located in identified flood hazard areas. Most communitiesjoined the NFIP after 1973 in order to make this assistance available for their flood-prone properties. NFIP flood insurance is available through many private flood insurance companies and independent agents, as well as directly from the federal government. All companies offer identical coverage and rates as prescribed by the NFIP. II -16 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 National Flood Insurance Program (NFIP) Pre-FIRMVersus Post-FIRM (Insurance Purposes) For flood insurance rating purposes, residential buildings are classified as being either pre-FIRM or post-FIRM. Please refer to Appendix A-The National Flood Insurance Pre-FIRM construction is defined as construction or substantial Program-for generalinformation improvement begun on or before December 31, 1974, or and an example of the costs of before the effective date ofthe community's initial FIRM, insurance coverage for structures weve is later. subject to various flooding whichever is later. scenarios. Post-FIRM construction includes construction or substantial improvementthat began after December31, 1974, or on or after the effective date of the community's initial FIRM, whichever is later. Insurance rates for pre-FIRM buildings are set on a subsidized basis; while insurance rates for post-FIRM structures are set actuarially on the basis of designated flood hazard zones on the community's FIRM and the elevation of the lowest floor of the building in relation to the BFE. This rate structure provides owners an incentive to elevate buildings in exchange for receiving the financial benefits of lower insurance rates. Subsequent to substantial improvements, apre-FIRM building may retain its pre-FIRMrate or become a post-FIRM building for flood insurancerating purposes. Only elevation or relocation techniques may result in reduced flood insurance premiums or in eliminating the need for flood insurance. EnaineerinaPrinciples and Practicesof Retrofittina Flood-ProneResidential Structures II -17 January 1995 Chapter II: Regulatory Framework sNFIP BUILDING _9 FLOOD-PRONE PERFORMANCE STANDARDS The NFIP has established minimum criteria and design perfor- ea mance standards that communities participating in the NFIP 10-OV IM must enforce for structures located in Special Flood Hazard Areas. These standards specify how a structure should be Communities often adopt flood- constructed in order to minimize or eliminate the potential for plain regulations that exceed the flood damage. NFIP minimum requirements. FEMA, the U.S. Army Corps of Engineers (USACE), the Tennessee Valley Authority (TVA), the Natural Resources Conservation Service (NRCS), and several states and local government entities have developed technical guidance manuals and information for public distribution to assist in the application ofthese requirements by the building community (i.e., building code and zoning officials, engineers, architects, builders, developers, and the general public). These publications, which are listedin Appendix C, GlossaryofResources, contain guidelines for the use of certain techniques and materials for design and construction that meet the intent ofthe NFIP 's general design criteria. These publications also contain information on the generally accepted practices for flood-resistant design and construction. FEMA has also undertaken a multi-year effort to incorporate the NFIP flood-damage-resistant design standards into the nation's model building codes and standards, which are then adopted by either states or communities. This effort has yielded the Code Compatibility Report, which examines the compatibility ofNFIP regulations, technical standards, and guidance with the model building codes/standards. II -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Community Regulations and the Permitting Process COMMUNITY REGULATIONS AND THE PERMITTING PROCESS Regulation ofthe use of floodplain lands is a responsibility of state and local governments and, in limited applications, the federal government (wetlands, navigable waterways, federal lands, etc.). It can be accomplished by a variety of procedures, such as establishment of designated floodways and encroachment lines, zoning ordinances, subdivision regulations, special The floodway is the channel of a use permits, floodplain ordinances, and building codes. These river or other watercourse and the land-use controls are intended to reduce or eliminate flood adjacent land areas that must be reserved in order to discharge the damage by guiding and regulating floodplaindevelopment. base flood without cumulatively increasingthe water surface As was explained in ChapterI, flood-prone communities that elevation more than a designated participate in the NFIP are required to adopt and enforce, at a height. minimum, NFIP-compliant floodplain regulations to qualify for many forms of federal disaster assistance and for the availability of flood insurance. Many states and communities have more restrictive requirements than those established by the NFIP. In fact, state and community officials, using knowledge of local conditions and in the interest of safety, may set higher standards, the most common of which are listed below. * Freeboard is the elevation difference between the flood protection elevation and the anticipated flood elevation. Freeboard requirements provide an extra measure of flood protection above the design flood elevation to account for waves, debris, hydraulic surge, or insufficient flooding data. * Restrictive standards prohibit building in certain areas, such as the floodplain, conservation zones, and the floodway. * The use of building materials and practices that have previously proven ineffective during flooding may be prohibited. Ennineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures II -19 January 1995 Chapter II: Regulatory Framework Before committing a significant investment oftime and money in retrofitting, the design professional should contact the local building official for building code and floodplain management requirements and information on obtaining necessary permits. II-20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Model Building Codes MODEL BUILDING CODES Several model codes and standards have been developed over a period of years under the auspices of various organizations. The most widely accepted model codes are: National Building Code: developed by the Building Officials and Code Administrators (BOCA), generally adopted by eastern and midwestern states; Standard Building Code: developed by the Southern Building Code Congress International (SBCCI), generally adopted by southern states; Uniform Building Code: developed by the International Council of Building Officials (ICBO), generally adopted by western states; One- and Two-Family Dwelling Codes: developed by the Council of American Building Officials (CABO), used for residential structures in various parts ofthe country; and NFPA Life Safety Codes: developed by the National Fire Protection Association (NFPA), used as a standard for fire protection in various parts of the country. Documents for each of the above codes follow standardized formats for content and references. Most model code groups also maintain product material evaluation reports, which contain specific testing information on a variety of building products. EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures H -21 January 1995 Chapter II: Regulatory Framework Table 1-3 Model Code Groups National Codes (BOCA): * BOCA National Building Code * BOCA National Fire PreventionCode * BOCA National Mechanical Code * BOCA National Plumbing Code * BOCA Property Maintenance Code StandardCodes (SBCCI): * Standard BuildingCode * Standard forFloodplainManagement * Standard MechanicalCode * Standard Gas Code * Standard PlumbingCode * Standard ExistingBuildingCode * Standard HousingCode * Standard Fire Prevention Code Uniform Codes (ICBO) * Uniform Building Code * UniformMechanical Code * International Plumbing Code * Uniform Fire Code * Uniform Housing Code NFPAStandards: * NFPA 101 -Life Safety Code * NFPA 70 -National Electrical Code * NFPA54 -National Fuel Gas Code * NFPA 58 -Standard for the Storage and Handling of Liquefied Petroleum Gases CABO One-and TWo-* CABO One-and Two-Family Dwelling Code Family Dwelling Code: Most communities have adopted model codes from one of these groups. Many of these codes have incorporated provi. 0-140 sions ofthe NFIP floodplain management regulations pertaining to building standards. States and local governments often make their own amend-FEMA is working closely with the model building code groups ments to the above codes. to ensurethatNFIP requirementswillbe accessible,credible, and easierto use and enforce by the building community. This ongoing effort is aimed at placing as many of the NFIP floodplain management requirements as possible into the model building codes. For more information on the model building codes, contact the local building and permitting officials or refer to the model code groups. I1 -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Code Compatibility with the NFIP CODE COMPATIBILITY WITH THE NFIP Given the variation in Istandards between model building codes, it is very important that the designer contact a local building official to ascertain any building code and/ or floodplain management requirements that would be unique to the specific retrofitting project or local jurisdiction. Designers should consult FEMA's Code Compatibility Report to gain a thorough understanding of how differences in NFIP standards and other codes affect the model code in use in a given community. The designer is responsible for determining a feasible resolution to these differences; it is recommended that designers obtain concurrence from local officials. Undercontract to FEMA, in 1992 the National Institute of Building Sciences (NIBS) consulted on an examination ofthe compatibilities between the NFIP regulations and technical guidance to the model codes. A report of this study-FEMA's CodeCompatibilityReport-provided a basis for coordinating NFIP documents with the model codes. It also represents a starting point for the preparation of a consensus flood-resistant constructionstandard. Table II-4 presents the general items that need to be reconciled between the model codes and NFIP requirements. Refer to the Code Compatibility Report for conflict resolution or the individual code documents for additional information. FnninAerinnPrinninlpqand Practirca nf Ratrofiftinn Flood-Prona Raeidantial Structuras II -23 January 1995 Chapter II: Regulatory Framework Table1-4 MODEL CODES/NFIP REQUIREMENTS: Items to be Reconciled ITEMS TO BE RECONCILED WITH THE NFIP BOCO SBCCI ICBO NFPA CABO Use of Registered Professionals X X Wind, Seismic & Snow Loads X X X X Footing & Slab Design X X X Standards for Use of Wood Materials X X X X Geotechnical Reports and Requirements for Open X X X X Foundations Corrosion Protection X X X Hydrostatic and Hydrodynamic Load Considerations and Computations X Occupancy in Basements Below the BFE X X X Consistency of Criteria for Residential and X Non-Residential Buildings X Anchorage Requirements X Exposed Ductwork X Utility Clearances X Standards for Sealants X Standards for Breakaway Walls X Design Tables Based on Materials X Design Considerations for Floodwalls X Protection of Electrical Systems Below the BFE X Grounded and Labeled Power Outlets for Pumps and X Motors Maintenance of Interior Finishes for Different Occupancies _ Complete Flood Design Criteria X X Alternate Forms or Means of Construction X Site Preparation Requirements X X Walls, Floor & Roof Sheathing Design X X X X X Vapor Barrier Requirements S X=ltem that must be reconciled between model codes and NFIR Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 CHAPTERIII _ _ g 1 0 S o 8 1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PARAMETERS OF RETROFITTING Featuring: Examination of Owner Preferences Community Regulations and Permitting Technical Parameters DPARAMETERS OF RETROFITTING K1~ EXAMINATION OF OWNER PREFERENCES Initial Homeowner Meetina Initial Site Visit Aesthetic Concerns Economic Considerations Risk Considerations Accessibility COMMUNITY REGULATIONSI AND PERMITTING LocalCodes Building Systemsl Code Upgrades Offsite Flooding Impacts TECHNICAL PARAMETERS Flooding Characteristics Site Characteristics Building Characteristics Historic Preservation Multiple Hazards 0 Chapter III: Parameters of Retrofitting Table of Contents Examination of Owner Preferences........................... III -2 The Initial Homeowner Meeting ........................... III -5 The Homeowner Learns: ........................... III -5 The Designer Learns: ........................... III -5 Initial Site Visit ........................... III -7 Aesthetic Concerns........................... III -9 Economic Considerations........................... III -9 Risk Considerations ........................... III -14 Accessibility for the Disabled ........................... III -15 Community Regulations and Permitting ........................... III -16 Local Codes ........................... III -16 Building Systems/CodeUpgrades ........................... III -16 Offsite Flooding Impacts ........................... III -17 TechnicalParameters ........................... III -18 Flooding Characteristics ........................... III -21 Flood Depth ........................... III -21 FloodVelocity ........................... III -24 Onset of Flooding ........................... III -25 Flood Duration ........................... III -25 Site Characteristics ........................... III -26 Site Location ........................... III -26 Soil Type ........................... III -27 Building Characteristics ........................... III -28 Substructure........................... III -28 Superstructure ........................... III -29 Support Services ........................... III -29 Building Construction ........................... III -31 BuildingCondition ........................... III -32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures HI January 1995 Balancing Historic Preservation Interests with Flood Protection .............................. III -35 Multiple Hazards .III -36 Flood-Related....a.a..s.......................................................................................... II-3 Flood-Related Hazards .................. III -37 Non-Flood-Related Hazards .. ....... III -38 : .0 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 PARAMETERS OF RETROFITTING In this chapter, the factorsthat influence retrofitting decisions areexamined and compared with various methods to determine the viability of specific retrofitting techniques. These factors include: * homeownerpreferences, * community regulations and permitting requirements, and * technical parameters. Factors such as homeowner preference and technical parameters are key elements in identifying appropriate retrofitting measures, while consideration ofthe multiple flood-related and non- flood-related hazards is critical in designing the retrofitting measure and/or avoiding the selection of a poor retrofitting method. This selection of alternatives can be streamlined through the use oftwo generic retrofitting matrices, which are designed to help the designer narrow the range offloodproofing options: PreliminaryFloodproofing/ Retrofitting PreferenceMatrix(FigureIII-1),which focuses on factors that influence homeowner preference and those measures allowable under local regulations. Retrofitting Screening Matrix (Figure III-3), which focuses on the objective physical factors that influence the selection of appropriate retrofitting techniques. Rninorn I II Drin,.rqi -Sndi DratjtirogQ nf Ratrnfiftinn Flood-Prnne Residential Structures III-1 Jauy-11VI I. alla .1995 . . January 1 995 Chapter III: Parameters of Retrofitting EXAMINATION OF OWNER PREFERENCES The proper evaluation of retrofitting parameters will require a series of homeowner coordination and design input meetings. Ultimately the homeowner will have to deal with the flood protection environment on a daily basis. Therefore, the functional and cosmetic aspects ofthe retrofitting measure, such as access, egress, landscaping, appearance, etc., need to be developed by including the homeowner's thoughts and ideas. Most retrofitting measures are permanent and should be considered similar to a major home addition or renovation project. The design should incorporate the concepts of those who will be using the retrofitted structure. Issues that should be addressed include: * retrofitting aesthetics, * economic considerations, * risk considerations, * accessibility, * local code requirements, * building mechanical/electrical/plumbingsystem upgrades, and * offsite flooding impacts. In order to avoid any future misunderstandings, designers should use their skills and knowledge of retrofitting projects to address technical implications while working with homeowners. Many owners have little or no technical knowledgeof retrofitting and naturally look to the designer or local official for guidance and expert advice. I11-2 Enaineerina Principles and Practices of Retrofittina Flood-Prone ResidAntial Strutinuire __- .-i, -J ry1995 January 1995 Examination of Owner Preferences The Preliminary Floodproofing/Retrofitting Preference Matrix,(FigureII-1), assiststhe designerin documenting the initial consultation with the homeowner. The first consideration, measure allowed by community, enables the designer to screen alternatives that are not permissible and must be eliminated from further consideration. Discussion of the considerations for the remaining measures should lead to a "no" or "yes" for each of the boxes. Examination ofthe responses will help the homeowner and designer select retrofitting measures for further examination that are both viable and preferable to the owner. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures 111-3 January 1995 Chapter Hi: Parameters of Retrofitting Owner Name: Prepared By: Address: Date: Property Location:, \Floodproofing riM 2 rfI Measures D__ a S Elevation Elevation Elevation Elevation Elevation Relocatior Dry Flood-Wet Flood-Floodwalls on on Fill on Plers on Posts on Piles proofing prooling and Foundation and Levees Considerations Walls Columns MeasureAllowed or Owner Requirement Aesthetic Concerns High Cost Concerns Risk Concerns Accessibility Concerns Code Required Upgrade Concerns Off-SilteFlooding Concerns TotalIRes= Instructions: Determine whether or not floodproofing measure is allowed under local regulations or homeowner requirement. Put an Yx"in the box for each measure which is not allowed. Complete the matrix for only those measures that are allowable (no Y in the first row). For those measures allowable or owner required, evaluate the considerations to determine if the homeowner has concerns which would impact its implementation. A concern is defined as a homeowner issue which if unresolved would makethe retrofitting method(s) infeasible. If the homeowner has a concem, place an Y in the box under the appropriate measure/consideration. Total the number of '1x's.' The floodproofing measure with the least number of "x's" is the most preferred. Figure II-1: PreliminaryFloodproofing/RetrofittingPreferenceMatrix m-4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Examination of Owner Preferences THE INITIAL HOMEOWNER MEETING The first step in the homeowner coordination effort is the educational process for both the designer and the property owner. This step is a very important one. The Homeowner Learns: * How it was determined that the home is in the floodplain; * Possible impacts of an actual flood; * Benefits offlood insurance; * Physical, economic, and risk considerations, and * What to expect during each step in the retrofitting process. The Designer Learns: * Floodhistoryofthe structure; * Homeowner preferences; * Financial considerations; * Special issues, such as accessibility requirements for the disabled, and * Informationaboutthe subjectproperty suchas: -topographic surveys, -site utility information, and -critical home dimensions. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter III: Parameters of Retrofitting During this initial meeting, the designer and homeowner should jointly conduct a preliminary assessment ofthe property to determine which portions ofthe structure require flood protection and the general condition ofthe structure. This initial evaluation will identify the elevation of the lowest floor and the elevation of potential openings throughout the structure through which floodwaters may enter the residence. 111-6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 The evaluation of information obtained during the initial meeting with the homeowner will help the designer and owner address the flood threat to the entire structure and the vulnerability of specific openings to floodwater intrusion. '000%0 Sometimes it is necessary for a field survey to be conducted by a professional land surveyor before design documents are developed. However, frequently the homeowner and designer may be able to develop a rough elevation relationship between the expected flood elevation, the elevation of the lowest floor, and the low points of entry to the structure sufficient for an initial evaluation. Examination of Owner Preferences INITIAL SITE VISIT A Low Point of Entry determination, illustratedin Figure III2, determines the elevation of the lowest floor and each of the structure's openings, and may include: * basement slab elevation; * windows, doors, and vents; * mechanical/electrical equipmentand vents; * the finished floor elevation of the structure; * drains and other floor penetrations; * water spigots, sump pump discharges, and other wall penetrations; * other site provisions that may require flood protection, such as storage sheds, wellheads, and storage tanks; and 0 the establishment of an elevation reference mark on or near the house. Oncethe LowPoint of Entrydeterminationhas beencom pleted, the designer/owner can determine the flood protection elevation andlor identify openings that need to be protected (in the case of dry floodproofing). PrnninIgmeanrd Practince nf Retrofittinfi Flood-Prone Residential Structures 111-7 January 1995 C1nsinmarinn Chapter III: Parameters of Retrofitting The approximate height of the retrofitting measure can be used by the owner and designer as they evaluate each of the ok',' parametersof retrofitting discussed in this chapter. In addition to determining the Low Point of Entry, this initial A detailed discussion of how to site visit should be used to assess the general overall condi evaluate the costs of different ti oft structure. alternatives and the effect of the tion ofthe structure. Low Point of Entry may be found in the chapter on Benefit/Cost Analysis. Low Point of Ent Low Point of EntV Utility Hazards Hose Bibrrf Lw rPintdow Entry A/C Unit A. SulpPm Electricf(Gas Meter 1 Dijcharg g I / II I. Ij / 1i I /-I …-/ II~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I L&--:-.i---owPoint of Entry --------1_________a______ u__t Windowor Door Sill Low Point of Ent Structural openin Dryer Vent Top of Window Wells Window or Door Sill Top of Areaway Stairwell Backflow Hazards \Lowest Floor Elevation Sanitary Sewers Top of Basement Slab or Top of First Floor Figure 111-2: Low Point of Floodwater Entry Survey for a Typical Residential Structure Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 ONIA I001W Sometimespropertyownersare reluctantto participatein retrofit- ting measures because they are concerned with how the work will alter the physical appearance of theirproperty.Suchreluctance maybe overcomewith avideo displayofbeforeandafterscenes of a building. This can be accom- plished with a personal computer (PC)anda video camera. ThePC canbe loadedwith a video capture card, whichwill allowtransferof a video image to the PC. The camcorder or VCR image is captured while in the pause mode andprojectedto the PCmonitor. Imagescanthenbe editedto portraythemin varioussurround- ings and with structure modifica- tions. These simulated pictures in color or black and white can be developed with currently available computer software. Examination of Owner Preferences AESTHETICCONCERNS Although physical and economic considerations may help determine feasible retrofitting measures forindividual buildings, the homeowners may consider other factors equally or more important. Aesthetics, for example, is a subjective issue. The homeowner may reject a measure that scores high for all considerations except aesthetics. On the other hand, what may be aesthetically pleasing to the homeowner may not be technicalyappropriateforaproject. Here,adesignermustuse skill and experience to achieve a common ground. In doing so, the homeowner's preference should be considered, while not jeopardizing the structural, functional, and overall success ofthe proposedproject. An aesthetically pleasing solution that also performs well as a retrofitting alternative can be achieved through an understanding ofthe relationship between the existing and proposed modifica .' aons,dcreativetreatmentand modificationofsurrounding landforms, proper landscaping techniques, and preservation of essential and scenic views. ECONOMIC CONSIDERATIONS At this point, the designer should not attempt to conduct a detailed cost analysis. Rather, general estimates ofthe cost of various retrofitting measures should be presented to the homeowner. As discussed in Chapter I, the cost of retrofitting will depend on avariety of factors including the building's condition, the retro fitting measure to be employed, the design flood elevation, the choice of materials and their local availability, the availability and limitations of local labor, and other site-specific issues (i.e., soil conditions and flooding levels) and other hazards. shiv Sz.. ll z*_l Structures 111^9 PininlIR Residential Ian Isvw~ llII r Dni~jnn snti Practices of RetrofittinaFlood-Prone Elyll:IIlljIIs; January 1995 Chapter III: Parameters of Retrofitting The following costs are nationwide averages that may need to be adjusted for local economic conditions. They were derived from various sources including the USACE document, Flood Proofing, How to Evaluate Your Options and various post-disaster documents prepared by FEMA as a result of the Midwest Flood of 1993, Hurricane Andrew in Florida (January 1993), the Northridge California earthquake (January 1994), and flooding in Southeast- em Texas (November1994). They are provided to assist in economic analysis and preliminary planning purposes. Table IlI-I Elevation and Relocation Cost Guide Type Elevation Relocation Per _______ ______ ______ Cost Cost Wood-Frame Building on Open Foundations $18 $28 square foot (Piles,Posts or Piers) Wood-Frame Building on Solid Foundation Walls $13 $23 square foot Brick Building $24 $39 square foot Slab-on-Grade Building $22 $37 square foot Table ll-Assumptions: 1. Elevation costs include foundation, extending utilities, and miscellaneous items, such as sidewalks and driveways. 2. Elevation unit cost is based on a 2-foot raise. Add $0.75 per square foot for each additional foot raise up to eight feet. Above 8 feet, add $1.00 per square feet. 3. Relocation costs include off-site relocation (less than 5 miles) and new site development for a 1,000 SF building. Extrapolation of this unit cost to larger buildings may result in artificially high estimates because the costs of relocation do not increase proportionally with building size. III-10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Examination of Owner Preferences -At IWf in relocating a structure, the cost of preparing the new site and cleaning up the old site must be considered. Table111-2Floodwalls and Levees Cost Guide Type Cost Per Floodwalls, two feet above ground level $77 linear foot Floodwalls, four feet above ground level $113 linear foot Floodwalls, six feet above ground level $160 linear foot Levees, two feet above ground level $34 linear foot Levees, four feet above ground level $63 linear foot Levees, six feet above ground level $105 linear foot Floodwall costs are based upon typical foundation depth of 30 inches. Levee costs are based upon typical foundation depth of one foot, 1 0-foot top width, and 1:3 side slopes. Levee costs include seeding and stabilization. Additional costs that may need to be estimated for both floodwalls and levees are as follows: Interior Drainage $3,800 lump sum Closures $66 square foot Riprap $28 cubic yard Sidewalk (3' wide) $9 linear foot Driveway (asphalt) $6 square yard Driveway (concrete) $16 square yard More detailed cost estimating guidance is provided in Chapters V and VI. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ;111-11 January 1995 Chapter III: Parameters of Retrofitting TablellI-3 Dry Floodproofing Cost Guide Type Cost Per Sprayed-on cement (1/8 inch) $3 square foot Asphalt (2 coats below grade) $1 square foot Periphery drainage $28 linear foot Plumbing check valve $600 lump sum Sump and pump installation $1,000 lump sum Table 111-4 Flood Shields Cost Guide Type Cost Per Metal $66 square foot Wood $21 square foot Additional costs which may be included: * temporary living quarters (displacement costs) thatmay be necessary during construction (estimate: relocation -3 to 4 weeks; elevation-2 to 3 weeks) * professional or architectural design (10% of thecosts of selected retrofitting measures), * contractors' profit (1 0% of the estimated costs), and * contingency to account for unknown or unusual conditions. Table III-5 can serve as a guide for developing the initial planning level estimate for each retrofitting alternative being considered. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Examination of Owner Preferences Table III-5 Preliminary Cost Estimating Worksheet Owner Name: Prepared By: Address: Date: Property Location: Cost Component Unit Unit Cost Quantity Total Subtotal Retrofitting Measure Contractor's Profit (10%) Design Fee (10%) (optional) Loss of Income (optional) . Displacement Expenses (optional) Contingency Subtotal Other Costs Total Costs Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 119L Chapter III: Parameters of Retrofitting RM RISK CONSIDERATIONS Another element that is included in the evaluation of retrofitting measures is the risk associated with a do-nothing approach. Risk can also be established among the various measures by knowing the exceedence probability offloods and the design flood levels for competing measures. Relocation is an example of how retrofitting can eliminate the risk of flood damage. On the other hand, a levee designed to protect against a 10percent chance annual exceedence probability (1 0-year) flood would have an 88-percent chance of being overtopped during a 20-year period. Such information will assist the homeowner in evaluating the pros and cons of each measure. Table III-6 provides the probabilities associated with one or more occurrences of a given flood magnitude occurring within a specific number of years. Table III-6 Flood Risk Frequency-RecurrenceInterval (Year-Event) 10 25 50 100 500 1 10% 4% 2% 1% 0.2% Length 10 65% 34% 18% 10% 2% Period 20 88% 56% 33% 18% 5% 25 93% 64% 40% 22% 5% 30 96% 71% 45% 26% 6% 50 99+% 87% 64% 39% 10% 100 99.99+% 98% 87% 63% 18% The table values representthe probabilities, expressed in percentages, of one or more occurrences of a flood of given magnitude or larger within a specified number of years. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 W Examination of Owner Preferences Flood probabilities are also useful in evaluating the homeowner inconvenience aspects of retrofitting. Reducing cleanup and repairs, lost time from work, and average non-use of a building from once in two years to once in ten years could be a powerful incentive for retrofitting even though other aspects may be less convincing. ACCESSIBILITY FOR THE DISABLED Accessibility for the disabled is an issue that must be addressed primarily on the specific needs ofthe owner. Many retrofitting measures can create access problems for a housethat was previously fullyaccessible. The Americans with Disabilities Act (ADA) of 1990 and the Fair Housing Amendment Act (FHA) of 1988 and other accessibility codes and regulations do not specifically address private single-family residences, which are the focus of this manual. However, the above-mentioned regulations contain concepts that may be of assistance to a designer representing a disabled property owner. It is important for the designer to remember that the term disabled does not refer only to someone who uses a wheelchair. Other disabilities may include: * limited mobility requiring the use of a walker or cane, which can inhibit safe evacuation; * a person's limited strength to open doors, climb stairs, install flood shields, or operate other devices; and * partial or total loss of hearing or sight. Special considerations such as small elevators may be needed. Discussion ofthe above factors with the homeowner and utilizationofthe PreliminaryRetrofittingPreference Matrix will allow the designer to rank the retrofitting methods by homeowner preference. Engineerina Principles and Practices of RetrofittingFlood-Prone Residential Structures 111-15 January 1995 Chapter III: Parameters of Retrofitting COMMUNITY REGULATIONS AND PERMITTING LOCAL CODES Most local governments regulate building activities by means of building codes as well as floodplain and zoning ordinances and regulations. With the intent of protecting health and safety, most local codes are fashioned around the model building codes Atp discussed in Chapter 1I. The designer should be aware that modifications may be undertaken to make the model codes A designershould become familiar more responsive to the local conditions and concerns in the withthe prevailing conditions, area, such as seismic and hurricane activity, extreme cold, or codes, and legal restrictions . particular to a building's location, Determination of which retrofitting measures are allowed under local regulations is an important step in compiling the Preliminary Floodproofing/Retrofitting Preference Matrix. Retrofitting measures not allowed under local regulations will be screened and eliminated from further consideration. BUILDING SYSTEMS/CODE UPGRADES Other local code requirements must be met by owners building improvements. Most building codes require approval when Somecommunities is considered, especially if structural modification and/ reque televation Some communities require that structures undergoing substantial or alteration and relocation of utilities and support services are rehabilitation, either because of involved. previous damage or significant improvements/additions, be broughtinto compliance with cIf more strigent laws have beensadopted since abuilding was current building codes. In constructed, local code restrictions can seriously affect the additionto floodplainmanage-selection of a retrofitting method because construction may be ment requirements, theserequire-expected to comply with new building codes. ments could include items such as the addition of fire alarms, removal of lead water pipes, upgrades in electrical wiring, etc. III -16 Enoineerino PrinciDles and Practices of Retrofittina Flood-Prone Residential Strutres _ ,_ _ -J ,._ ...... . __..__ ; n..___ . ............. _.__....January. 1995 January 1 995 Community Regulations and Permitting Addressing offsite impacts and issues is as much a matter of responsible practice and con science as it is a requirement of most building codes and floodplain management ordinances. NFIP, state, and local regulations do not allow construction within a floodway or, in some cases, within a floodplain that would back up and increase flood levels. OFFSITE FLOODING IMPACTS Where a chosen retrofitting measure requires the modification of site elements, a designer shall consider how adj acent properties will be affected. * Will construction of levees and floodwalls create diversions in the natural drainage patterns? * Will new runoffs be created that may be detrimental to nearby properties? * If floodproofing disturbs the existing landscape, will regrading and relandscaping undermine adjacent streets and structures? * Will the measure be unsightly or increase the possibility of sliding and subsidence at a later date? * If a building is to be relocated to another portion of the current site, or if it is to be elevated, will it encroach on established easements or rights-of-way? * Will the relocated building infringe on wetland areas or regulated floodplains? These and other questions must be addressed and satisfactorily answered by the designer and homeowner in selecting the most appropriate retrofitting measure. Both must be aware of the liabilities that may be incurred by altering drainage patterns and other large-scale site characteristics. The designer should insure that any modified runoffs do not cause negative impacts on the surrounding properties. The means necessary to collect, conduct, and dispose of unwanted flood or surface water resulting from retrofitting modifications must be understood and clearly resolved. Enaineerina Principles and Practices of F letrofittina Flood-Prone Residential Structures III- 17 January 1995 Chapter III: Parameters of Retrofitting TECHNICAL PARAMETERS 'Once the designer has resolved preliminary retrofitting prefer ence issues with the owner, a more intensive evaluation ofthe technical parameters is nonnally conducted, including flooding, site, and building characteristics. Figure 111-3 provides a Retrofitting Screening Matrix (worksheet) that can be used to evaluate which measures are appropriate for individual struc tures. Instructions forusing this matrix are presented in Figure 111-4. The remainder ofthis chapter provides background information on each of the technical parameters, which will be useful to the designer in completing the Retrofitting Screening Matrix. IEI-18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures .lam I1ll I car, ..c.. c y .-rr .. Technical Parameters Owner Name: Prepared By: Address: Date: Property Location: Measures levation Elevation Elevation Relocation Dr Flood Wet Flood Floodwalls .on ; on Fill on Piers, proofing proofing and Foundation Piles, Levees Walls Posts,and -Parameters--: : Columns Measure Permitted by Community or Preferred by Homeowner : . FloodDepth _ ___ Shallow (<3 feet) ___ I Moderate (3 to 6 feet) __ WA . NIA Deep (>6 feet) -WN/A N/A N/A ti; Flood Velocity Slow/Moderate (s5 fps) A Fast (>5 fps) 1 1 1 WNA | 1 im Flash Flooding ii Yes (<1 hour) 1 r T 2 1 2 8 No _ L11 Ice and Debris Flow _ . Yes No 3Site Location 0 6 _ 4 N/A 11 j j 4 i Floodway OtherA Zone 1 T T 5 T I 5 | 5 5T 5 5 Soil Type 0 Permeable l | 3 | 3 c5 Impermeable 1 - 0 Building Foundation Slab on Grade i Crawl Space _ I _ _ __A .-Basement | 6 |6 | | 6 1 r E Building Construction (Framing) 5 Concrete or Masonry _ _ | ' Wood and Others _Building Condition Excellent to Good Fair to Poor 6 6 6 6 6 Figure I11-3: Retrofitting Screening Matrix Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III- 19 January 1995 Chapter III: Parameters of Retrofitting r The Retrofitting Screening Matrix (Figure 111-3)is designed to screen and eliminate retrofitting techniques that should not be considered for a specific situation. Step 1: Screen alternatives which are not permitted nor preferable to the homeowner and are eliminated from further consideration, by inserting NIP (not permitted) in the appropriate box(es) on the Measures Permitted by Community row. If a N/P is placed in a column representing a retrofitting measure, that alternative is eliminated from consideration. Step 2: Select the appropriate row for each of the nine characteristics that best reflect the flooding, site, and building characteristics. Step 3: Circle the N/A (not advisable) boxes that apply in the rows of characteristics selected. Do not circle any N/A boxes where there Is a plan to engineer a solution to address the specific characteristic. Step 4: Examineeach column representing the different retrofitting measures. If one or more NIA boxes are circled in a column representing a retrofitting measure, that alternative is eliminated from consideration. Step 6: The numbers enclosed in the boxes represent special considerations (detailed below) which must be accounted for to make the measure applicable. If the consideration cannot be addressed, the number should be circled and the measure eliminated from consideration. Step 6: Retrofitting measures that remain should be further evaluated for technical, benefit-cost, and other considerations. A preferred measure should evolve from the evaluation. NIA Not advisable in this situation. NIP Not permitted in this situation. 1 Fast flood velocity is conducive to erosion and special features to resist anticipated erosion may be required. 2 Flash flooding usually does not allow time for human intervention; thus, these measures must perform without human intervention. Openings in foundation walls must be large enough to equalize water forces and should not have removable covers. Closures and shields must be permanently in place, and wet floodproofing cannot include last-minute modifications. 3 Permeable soils allow seepage under floodwalls and levees; therefore, some type of subsurface cutoff feature would be needed beneath structures. Permeable soils become saturated under flood conditions, potentially increasing soil pressures against a structure, therefore some type of foundation drain system or structure may be needed. 4 Ice and debris loads should be considered and accounted for in the design of foundations and floodwall/evee closures. 5 Any retrofitting alternative considered for the floodway must meet NFIP, state, local, and community floodplain requirements concerning encroachment/obstruction of the floodway conveyance area. 6 Not advisable in this situation, unless a specific engineering solution is developed to address the specific characteristic or constraint. Figure III-4: Instructions for Retrofitting Screening Matrix III -20 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures January 1995 Technical Parameters FLOODING CHARACTERISTICS Riverine flooding is usually the result of heavy or prolonged rainfall or snowmelt occurring in upstream inland watersheds. In some cases, especially in and around urban areas, flooding can also be caused by inadequate or improper drainage. In coastal areas subject to tidal effects, flooding can result from wind-driven and prolonged high tides, poor drainage, storm surges with waves, and tsunamis. There are several different flood characteristics that must be examined to determine which retrofitting measure will be best suited for a specific location. These characteristics not only indicate the precise nature of flooding for a given area, but can also be used to anticipate the performance of different retrofitting measures. These factors are outlined below. Flood Depth Determining the potential depth of flooding for certain flood frequencies is a critical step because it is often the primary factor in evaluating the potential for flood damage. A building is susceptible to floods of various depths. Floods of greater depth occur less frequently than those of lesser depths. Potential flood elevations from significant flooding sources are shown in Flood Insurance Studies (FIS) for most participating NFIP communities. For the purpose of assessing the depth of flooding a structure is likely to endure, it is convenient to use the flood levels shown in the study, historical flood levels, and flood information from other sources. The depth of flooding affecting a structure can be calculated by determining the height of the flood above the ground elevation at the site of the structure. Engineering Principles and Practices of R Retrofitting Flood-Prone Residential Structures III -21 January 1995 Chapter III: Parameters of Retrofitting [1-5: Photographs showing mud lines on homes are a source of historical information. [Hydrostatic fames _~~~~~~~~ i_V w1101w 711 Buoyancyor uplift forces increasewth lood depth. Figure 111-6: Hydrostatic Forces For those areas outside the limits of an FIS or state, community, or privately prepared local floodplain study, determination of flood depth may require a detailed engineering evaluation of local drainage conditions to develop the necessary relationship between flow (discharge), water-surface elevation, and flood frequency. The designer should contact the local municipal engineer, building official, or floodplain administrator for guidance on computing flood depth in areas outside existing study limits. Floodwaters can impose hydrostatic forces on buildings. These forces result from the static mass of water acting on any point where floodwater contacts a structure. They are equal in all directions and always act perpendicularly (or normally) to the surfaces on which they are applied. Hydrostatic loads can act vertically on structural members such as floors and decks (buoyancy forces) and laterally (hydrostatic forces) on upright Ill -22 EngineeringPrinciples and Practices ofRetrofitting Flood-Prone Residential Structures January 1995 Technical Parameters structural members such as walls, piers, and foundations. Hydrostatic forces increase linearly as the depth of water increases. Figure III-6 illustrates the hydrostatic forces generated by water depth. If a well-constructed building is subject to flooding depths of less than three feet, it is possible that unequalized hydrostatic forces may not cause significant damage. Therefore, consideration can be given to using barriers, sealants, and closures as retrofitting measures. If shallow flooding (less than three feet) causes a basement to fill with water, wet floodproofing methods can be used to reduce flood damage to basements. If a residential building is subject to flooding depths greater than three feet, elevation or relocation are often the most effective methods of retrofitting. Water depths greater than three feet can often create hydrostatic forces with enough load to cause structural damage or collapse if the house is not moved or elevated. One other potential method (provided the cost is not prohibitive) is the use of levees and floodwalls designed to withstand flooding depths greater than three feet. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III-23 January 1995 Chapter III: Parameters of Retrofitting Flood Velocity The speed at which floodwaters move (flood flow velocity) is normally expressed in terms of feet per second (fps). As floodwater velocity increases, hydrodynamic forces imposed by moving water are added to the hydrostatic forces from the depth of still water, significantly increasing the possibility of structural failure. Hydrodynamic forces are caused by water The use of existing and historical moving around an object and consist of positive frontal pressure data can be very useful in analyz-against the structure, drag forces along the sides, and negative ing the flood threat. Through interviews with residents, approxi-pressures on the building's downstream face. Greater velocities mate dates of flooding may be can quickly erode, or scour, the soil supporting and/or sur- established, as well as remem-rounding buildings. Thus, the impact drag, and suction from bered depths of flooding, types of these fast-moving waters may move a building from its foundavelocity (moving or standing tion or otherwise cause structural damage or failure. water), duration of flooding, etc. Once the dates have been established, the designer can check Unfortunately, there is usually no definitive source of information other sources such as newspapers to determine potential flood velocities in the vicinity of specific and the National Weather Service buildings. Hydraulic computer models or hand computations for additional information. based on existing floodplain studies may provide flood velocities in the channel and overbank areas. Where current analysis data is not available, historical information from past flood events is probably the most reliable source. Figure 111-7: Fast-moving floodwaters caused scour around the foundation and damage to the foundation wall. III-24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Flash flooding will usually preclude the use of any retrofitting measure that requires human intervention. Technical Parameters Onset of Flooding In areas of steep topographyor those areas with a small drainage area, floodwaters can rise very quickly with little or no warning. This condition is known as flash flooding. High velocities usually accompany these floods and may preclude certain types of retrofitting, especially those requiring human intervention. In a flash flooding situation, damage usually begins to occur within one hour after significant rainfall. Ifa building is susceptible to flash floods, insufficient warning time can preclude the installation of shields on windows, doors and floodwalls, as well as the activation of pump systems and backup energy sources. Temporarily relocating movable contents to a higher level may also be impractical. However, such measures may be effective if a building is not subject to flash flooding and the area has adequate flood warning systems, such as television -vs~~~~~~~ A detailed hydrograph can provide information on duration of flooding. However, such information is usually not available, and the cost of creating a new study is usually prohibitive. One potential source of information is to check similarly sized drainage basins in neighboring areas to see if historical data exists. and radio alerts. Flood Duration In areas of long-duration flooding, certain measures such as dry floodproofing may be inappropriate due to the increased chance of seepage and failure caused by prolonged exposure to floodwaters. Engineering Principles and Practices of F RetrofittingFlood-ProneResidential Structures III -25 January 1995 ChapterIII: Parameters of Retrofitting 611% SITE CHARACTERISTICS Site characteristics such as location, underlying soil conditions, and erosion vulnerability play a critical role in the determination of an applicable retrofitting method. Site Location The floodplain is usually defined as the area inundated by a floodhhaving a 100-year floodfrequency. The riverine floodplain is often fbrther divided into a floodway and a floodway flinge. As defined earlier, the floodway is the portion ofthe floodplain that contains the channel and enough ofthe surrounding land to enable floodwaters to pass without increasing flood depths greater than a predetermined amount. If there are high flood depths and/or velocities, this area is the most dangerous portion ofthe riverine floodplain. Also, since the floodway carries most ofthe flood flow, any obstruction may cause floodwaters to back up and increaseflood levels. For these reasons,the NFIP and local communities prohibit new construction or substantial improvement in identified floodways that would increase flood levels. Relocation is the recommended retrofitting option for a structure located in a floodway. Community and state regulations may prohibit elevation of structures in this area. However, elevation on an open foundation will allow for more flow conveyance than a structure on a solid foundation. The portion ofthe floodplain outside the floodway is called the floodway fringe. This area normally experiences shallower flood depths and lowervelocities. With proper precautions, it is often possible to retrofit structures in this area with an acceptable degree of safety. III-26 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures January 1995 Technical Parameters / SATURATED / SOIL Figure 111-8: Lateral Forces Resulting From Saturated Soil Figure 111-9: Buoyancy Forces Resulting From Saturated Soil Contact the local office of the Natural Resource Conservation Service (NRCS) or a local geotechnical engineering firm to obtain guidance on the permeability or consolidation features of soils native to the area. Because the site may have been backfilled with non-native materials during original construction, NRCS data should be used carefully. Soil Type Permeable soils, such as sand and gravel, are those that allow groundwater flow. In flooding situations, these soils may allow water to pass under floodwalls and levees unless extensive seepage control measures are employed as part of the retrofit-) ting measures. Also, saturated soil pressure may build up against basement walls and floors. These conditions cause seepage, disintegration of certain building materials, and structural damage. Levees, floodwalls, sealants, shields, and closures may not be effective in areas with highly permeable soil types. Saturated soils subject horizontal surfaces, such as floors, to uplift forces, called buoyancy. Like lateral hydrostatic forces, buoyancy forces increase in proportion to the depth of water/ saturated soil above the horizontal surface. Figures 111-8 and III-9 illustrate the combined lateral saturated soil and buoyancy forces. For example, a typical wood-frame home without a basement or proper anchoring may float if floodwaters reach three feet above the first floor. A basement without floodwater in it could fail when the ground is saturated up to four feet above the floor. Uplift forces occur in the presence of saturated soil. Therefore, well-designed, high-capacity subsurface drainage systems with sump pumps may be an effective solution and may allow the use of dry floodproofing measures. Other problems with soil saturated by floodwaters need to be considered. If a building is located on unconsolidated soil, wetting ofthe soil may cause uneven (differential) settlement. The building may then be damaged by inadequate support and subject to rotational, pulling, or bending forces. Some soils, such as clay or silt, may expand when exposed to floodwaters, causing massive forces against basement walls and floors. As a result, buildings may sustain serious damage even though floodwaters do not enter or even make contact with the structure itself. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III -27 January 1995 Chapter III: Parametersof Retrofitting BUILDING CHARACTERISTICS Ideally, a building consists of three different components: substructure, superstructure, and support services. The substructure consists ofthe foundation system; the superstructure consists ofthe portion ofthe building envelope above the foundation system. The support services are those elements that are introduced into a building to make it habitable. These components are integrally linked together to help a building maintain its habitability and structural integrity. Any action that considerably affects one may have a minimal or sometimes drastic effect on the others. An understanding of building characteristics and types of construction involved is therefore an important consideration in deciding upon an appropriate retrofitting measure. Substructure The substructure of a building supports the building envelope. It includes components found beneath the earth's surface, as B*y well as above-grade foundation elements. This system consists of both the vertical foundation elements such as walls, posts, A cracked foundation is one idcratio fo a weakoundion. piles, and piers, which support the building loads and transmit indication of a weak foundation. The use of floodwalls and levees them to the ground, and the footings that bear directly on the may be the easiest and most soil. practical approach to retrofitting a structure with a poor foundation. At any given time, there are a number of different kinds of relocation of the building's super-loads acting onabuilding. Thefoundationsystemtransfers structure onto a new foundation. these loads safely into the ground. In addition to dead and live loads, retrofitting decisions must take into account the buoyant uplift thrust on the foundation, the horizontal pressure of floodwater against the building, and any loads imposed by multiple hazards such as wind and earthquake events. The ability ofa foundation system to successfully withstand these and other loads or forces, directly or indirectly, is dependent to a large extent on its structural integrity. A designer should determine the type and condition ofa building's foundation system early in the retrofitting evaluation. III -28 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures January 1995 Technical Parameters All foundations are classified as either shallow or deep. Shallow foundations consist of column and wall footings, slab-ongrade, crawl space, and basement substructures; deep foundations include piles. Even though each ofthese foundation types Retrofittingof structures with may be utilized either individually or in combination with others, basements is not covered in this most residential buildings located outside coastal high hazard manual. areas are supported on shallow foundations. Each type has its own advantages and limitations when retrofitting measures are being evaluated. Whichever is used in a building, a designer should carefully check for the structural soundness of the foundation system. Basement walls may be subject to increased hydrostatic and buoyancy forces; thus, retrofitting a building with a basement is often more involved and costly. Superstructure The superstructure is the portion of the building envelope above the foundation system. It includes walls, floors, roof, ceiling, doors, and other openings. A designer should carefully and thoroughly analyze the existing conditions and component parts ofthe superstructure to determine the best retrofitting options available. Flood- and non-flood-related hazard effects should also be considered; the uplift, suction, shear, and other pressures exerted on building and roof surfaces by wind and other environmental hazards may be the only reasons needed to rule out elevation as a retrofitting measure. Support Services These are elements that help maintain a human comfort zone and provide needed energy, communications, and disposal of water and waste. For a typical residential building, the combina tion ofthe mechanical, electrical, telephone, cable TV, water supply, sanitary, and drainage systems provides these services. An understanding ofthe nature and type of services used in a building is necessary for a designer to be able to correctly predict how they may be affected by retrofitting measures. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures III -29 January 1995 Chapter III: Parameters of Retrofitting I I For example, the introduction of new materials or the alteration ofabuilding's existing features may require resizing existing services to allow forthe change in requirements. Retrofitting may also require some form of relocated ductwork and electrical rewiring. Water supply and waste disposal systems may have to be modified to prevent future damage. This is particularly true when septic tanks and groundwater wells are involved. If relocation is being considered, the designer must consider all these parameters and weigh the cost of repairs and renovation against the cost of total replacement. 1I -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 For general consideration of retrofitting measures, all construction should be classified as wood material unless all walls and foundations are concrete and masonry. Technical Parameters Building Construction Modem buildings are constructed with a limitless palette of materials integrated into various structural systems. A building may be constructed with a combination of various materials. Thus, the suitability of applying a specific retrofitting measure may be difficult to assess. Concrete and masonry construction may be considered for all types of retrofitting measures, whereas other materials may not be structurally sound or flood-damage resistant and therefore not suitable for some measures. When classifying building construction as concrete and masonry, it is important that all walls and foundations be constructed of this material. Otherwise, there may be a weak link in the retrofitting measure, raising the potential for failure when floods exert hydrostatic or hydrodynamic forces on the structure. Masonry-veneer-over-wood-frame construction must be identified since wood-frame construction is less resistant to lateral loading than a brick-and-block wall section. Engineering Principles and Practicesof Retrofitting Flood-ProneResidential Structures Ill -31 January 1995 Chapter III: Parameters of Retrofitting 'now. | Building Condition A building's condition may be difficult to evaluate, as many structural defects are not readily apparent. However, careful inspection ofthe property should provide for a classification of "excellent to good" or "fair to poor." This classification is only Typically,a designer will begin a for the reconnaissance phase of selecting appropriate retrofitting retrofitting project with an initial measures. More in-depth planning and design may alter the analysis of the present conditions. initial judgment regarding building condition, thereby eliminating Decisions based on early findings may be revised after a more some retrofitting measures from consideration at a later time. detailed analysis. Analysis ofa building's substructure, superstructure, and support services may be done in two stages-an initial analysis usually based on visual inspection, and a detailed analysis (discussed in Chapter VI) which is often more informative, involves greater scrutiny, and usually requires detailed engineering calculations. In the course of an analysis, a designer should visually inspect the walls, floors, roof, ceiling, doors, windows, and S other superstructure and substructure components. Walls should be examined for type of material, structural stability, cracks, and signs of distress. A crack on a wall or dampness on concrete, plaster, wood siding, or other wall finishes may be a sign of concealed problems. Doors, windows, skylights, and other openings should be checked for cracks, rigidity, structural strength, and weather resistance. Metal-clad wood doors or panel doors with moisture- resistant paint, plastic, or plywood exterior finishes may appear fine even though the interior cores may be damaged. Aluminum windows may be checked for deterioration due to galvanic action or oxidation from contact with floodwater. Steel windows may be damage-free if they are well protected against corrosion. Wood windows require inspection for shrinkage and warping, and for damage from moisture, mold, fungi, and insects. Flooring in a building can include a vast range of treatments. It involves the use of virtually every material that can be walked S III -32 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures January 1995 Technical Parameters upon, from painted concrete slabs to elegant, custom-designed wood parquet floors. A designer should investigate the nature of both the floor finishes and the underlying subfloor. Vinyl or rubberized plastic finishes may appear untouched due to their resistance to indentations and water; however, the concrete or wood subfloor may have suffered some damage. Likewise, a damage-free subfloor may be covered with a scarred finish. An initial analysis of the conditions of the roof and ceiling of a building can be done by observation during the early decision- making stage. An understanding of the materials and construction methods will be necessary at a later date to evaluate fully the extent of possible damage and need to retrofit. The roofs over most residential buildings consist of simple to fairly complex wood framing that carries the ceilings below and plywood roof decks above, over which the roof finishes are placed. Finish materials include asphalt, wood, metal, clay and concrete tile, asbestos, and plastic and are available in various compositions, shapes, and sizes. In some cases, observation may be enough to determine the suitability, structural rigidity, and continuing durability of a roof system. However, it may be necessary to pop up a ceiling tile; remove some shingles, slate, or roof tiles; or even bore into a roof to achieve a thorough inspection. The inspection also determines if the building materials and component parts are sound enough for the building easily to undergo either elevation, relocation, or wet or dry floodproofing. If not, floodwalls or levees around the structure may be the best alternative if allowable. Figure III- 10 presents a template that a designer can utilize to document findings during the initial building condition survey. Enaineerina PrinciDles and Practices of IRetrofittina Flood-Prone Residential Structures 111-33 January 1995 Chapter III: Parameters of Retrofitting Owner Name: Prepared By: Address: Date: Property Location: Preliminary Building Condition Evaluation Worksheet Condition Building Components Excelleto i Notes and Materials Good Fi oPo Substructure Footings Foundation Foundation Walls Other Superstructure Floors Walls Ceilings Doors Windows Roof Other Support Services Heating System Plumbing System Air Conditioning System Water Supply Sewage Other Comments Figure 111-10: Preliminary Building Condition Evaluation Worksheet III -34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Technical Parameters BALANCING HISTORIC PRESERVATION INTERESTS WITH FLOOD PROTECTION Many historic building features were developed, either deliber ately or intuitively, as responses to natural and environmental hazards, and to local climate or topography. Recognizing how and why these features were intended to work can help in designing a program of'preventive measures that is historically appropriate and that minimizes incongruous modifications to historic residential properties. There are retrofitting steps that will not have a negative or even significant impact upon the historic character of a site or its particular features. Preventive measures can be carried out without harming or detracting from historic character, as long as design and installation arepcarefully supervised by a professional knowledgeable in historic preservation. There may well be instances, however, when~a measure' that best protects the site also may result in some loss of historic character. In such a case, the designer and the owner will have to weigh the costs of compromising character or historic authenticity against the benefits of safeguarding the site or a particular site feature against damage or total destruction. One example of such a choice is the decision whether to elevate a historic structure located in a flood hazard area, relocate it out of the area, retrofit it with wet or dry floodproofing techniques, or leave it in its existing state to face the risks of damage or loss. It is difficult to prescribe a formula for such a decision, since each situation will be unique, considering location, structural or site conditions, the variety of preventive alternatives available, cost, and degree of potential loss of historic character. Here are some questions the designer may wish to pose in deliberating such a decision: *What is the risk that the historic feature or the entire site could be totally destroyed or substantially damaged if the Enaineerina PrinCiolesand Practices of I :IetrofittinaFlood-Prone Residential Structures 1II1-35 January 1995 Chapter III: Parameters of Retrofitting 'g--v |preventive measure is not taken? Ifthe measure is taken, to what degree will this reduce the risk of damage or total destruction? Are there preventive alternatives that provide less protec tion from flood damage but also detract less from historic character?What are these, and what is the trade-off between protection and loss of character? * Is there a design treatment that could be applied to the preventive measure to lessen detraction of historic character? MULTIPLE HAZARDS The selection of a retrofitting method may expose the structure to additional non-flood environmental hazards that could jeopardize the safety ofthe structure. These multiple hazards can be accommodated through careful design ofthe retrofitting measures or may necessitate selection ofa different retrofitting method. Multiple hazards include both flood-related and non-flood-relatedhazards. Information concerning the analysis and design for these multiple hazards is contained in Chapters IV and VI. The significant flood-related hazards to consider include ice and debris flow, impact forces, erosion forces, and mudslide or alluvial fan impacts. The major non-flood-related hazards to consider include earthquake and wind forces. Less significant hazards addressed in Chapter IV include land subsidence, fire hazards, snow loads, movable bed streams, and closed basin lakes. Multihazards may affect a structure independently, as with flood and earthquakes, or concurrently, as with flood and wind in a coastal area. I11-36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 It is importantto consider these multiple hazards when screening and selecting a retrofitting measure. However, the designer should be aware that structures can be engineered to withstand these multiple hazards, and the existence of these hazards alone may not oustifytheseliiatirdsalonemspedebris nof justify the elimination of specific homeowner-preferred retrofitting methods. The local buildingcodes normallycontain additional guidanceconcerningnatural hazard-resistant designand construction practices. Technical Parameters Flood-Related Hazards IMPACT FORCES -ICE AND DEBRIS FLOW In colder climates, floodwaters may carry chunks of ice that can act as a battering ram on a structure. During a flood, ice can also form around the structure. Rising floodwaters can lift a structure, resulting in severe damage. Flash and high-velocity floodwaters often carry debris such as cars, sheds, boulders, rocks, and trees that can destroy most retrofitting measures as well as the structure itself. Retrofitting measures suitable for areas of ice and debris flow may include elevation on fill, relocation, levees, and armored floodwalls. EROSION FORCES If a soil is highly erodible, fast-moving floodwaters can undermine foundations and cause building, levee, or floodwall failures. The consideration of soil erosion is critical when retrofitting a building located in the floodplain. With the exception of deep foundation systems such as piles, shallow foundation systems generally do not provide sufficient protection against soil erosion without some type of protection or armoring measure of below- grade elements. The local office ofthe Natural Resources Conservation Service (NRCS) will generally have information concerning the erodibility ofthe soils native to a specific site. ALLUVIAL FANS Because ofthe potential for high flood velocities, significant flow, and varying channel locations, alluvialfans present many unique challenges. In the upper portions of the fan, the only feasible retrofitting technique may be relocation. However, on lower portions ofthe fan where the flood velocities and depths are low, several options may be available. The hazards associated with alluvial fan flooding are discussed in detail in Appendix D of this manual. EnaineerinaPrinciDles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Chapter III: Parameters of Retrofitting FEMA is currently involved in an interagency task force developing earthquake-resistant design standards in the wake of recent disasters. For additional information contact FEMA's Mitigation Directorate or the appropriate Regional FEMA office. If At' Strengthening an existing masonry block foundation wall can be complicated and normally requires the expertise of a designer knowledgeable in this type of work. The local building codes may contain additional guidance concerning earthquake-resistant design and construction materials. Non-Flood-RelatedHazards EARTHQUAKE FORCES Earthquake protection steps can be divided into two categories: steps that deal with the building structure itself, and steps that can be taken with other parts of the building and its contents. The most important step for the structure is making sure that it is properly bolted down onto its foundation so it will not slide off in an earthquake. Another important step, especially if the foundation is being raised to place the structure above flood levels, is to make sure the foundation can withstand an earthquake. For masonry block foundations, this usually means strengthening key portions ofthe wall by installing reinforcing bars in the blocks and then filling them with concrete grout. WIND FORCES High winds impose forces on a home and the structural elements of its foundation. Damage potential is increased when the wind forces occur in combination with flood forces. In addition, as a structure is elevated to minimize the effects of flood forces, the wind loads on the elevated structure may be increased. A conventional structure is normally built to resist vertical downward loads (its own weight) plus live loads (contents, people) on the floor and snow and wind loads on the roof Occasionally, structural elements are laid on top of each other with minimal fastening. However wind forces can be upwards, or from any direction exerting considerable pressure on structural components such as walls, roofs, connections, and anchorage. Therefore, wind loads should be considered in the design process at the same time as hydrostatic, hydrodynamic, and impact dead and live loads as prescribed under the applicable codes. III-38 Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures January 1995 CHAPTER IV -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~" DETERMINATION OF HAZARDS Featuring: Analysis of Flood-Related Hazards Analysis of Non-Flood-Related Hazards Geotechnical Considerations DETERMINATIONOF HAARDS ANALYSIS OF FLOODRELATED HAZARDS ANALYSIS OF NON-FLOODRELATED HAZARDS I GEOTECHNICAL CONSIDERATIONS Flood Depth Wind Forces Bearing Capacity Hydrostatic Forces Seismic Forces Scour Potential l Hydrodynamic Forces Land Subsidence Frost Zone Impact Forces Permeability Riverine Erosion Shrink-Swell Potential Interior Drainage Alluvial Fans Closed Basin Lakes K Movable Bed Steams I 2.11 Chapter IV: Determination of Hazards Table of Contents Analysis of Flood-Related Hazards ............................................................ IV -2 Flood Depth ............................................................ IV -2 Riverine Areas ............................................................ IV -2 Coastal Areas ............................................................ IV -6 Hydrostatic Forces ............................................................. IV -10 Lateral Hydrostatic Forces................... ......................................... IV -11 Saturated Soil Forces............................................................... IV -12 Combined Water and Saturated Soil Forces ........................................................IV -15 Vertical Hydrostatic Force .............................................................. IV -17 Hydrodynamic Forces ............................................................... IV -20 Low Velocity Hydrodynamic Forces ......................................................... ... IV -21 High Velocity Hydrodynamic Forces ............................................................ IV -25 Impact Loads ............................................................ IV -29 Normal Impact Forces .............................................................. IV -30 Special Impact Forces............................................................... IV -31 Extreme Impact Forces.............................................................. IV -32 Riverine Erosion .............................................................. IV -35 Interior Drainage.............................................................. IV -36 Alluvial Fan Flooding Hazards .................... ......................................... IV -40 Bulking Factor.............................................................. IV -41 Hydrostatic and Hydrodynamic Loads............................................................ IV -42 Freeboard.............................................................. IV -43 Safety Factors .............................................................. IV -44 Closed Basin Lakes ............................................................ IV -46 Movable Bed Streams ............................................................ IV -47 Analysis of Non-Flood-Related Hazards ....................... ..................................... IV -48 Wind Forces.............................................................. IV -48 SeismicForces ............................................................ IV -50 Protection of the Structure ................... ......................................... IV -52 Protection of Non-Structural Building Components and Building Contents .......IV -53 Land Subsidence .............................................................. IV -53 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV - January 1995 Geotechnical Considerations........................ IV -55 Bearing Capacity .. ................. IV -58 Scour Potential ................ IV -60 Frost Zone Considerations ................ IV -68 Permeability ................. IV -68 Shrink-Swell Potential.................. IV -70 IV -ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 DETERMINATION OF HAZARDS Chapters I through III introduced retrofitting and guided the designer through the technical process of pre-selecting retrofitting techniques for consideration. In this chapter, the analyses necessary to determine the flood-and non-flood-related forces and other site- specific considerations that control the design of a retrofitting measure are presented. This informationmay be useful in preparing benefit/cost analyses and determining which retro fitting alternatives are infeasible. The analysis of hazards contributes to the design criteria for retrofitting measures, which are described in Chapter VI. Retrofitting measures must be designed, constructed, connected, and anchored to resist flotation, collapse, and movement due to all combinations of loads appropriate to the situation, including: * flood-related hazards, such as hydrostatic and hydrodynamic forces, impact forces, interior drainage considerations, and the effects of erosion; * site-specific flood-related hazards, such as alluvial fans, closed basin lakes, and movable bed streams; * non-flood-related environmental loads, such as earthquake and wind forces and land subsidence; and * site-specific soil or geotechnical considerations, such as soil pressure, bearing capacity, scourpotential, shrink-swell potential, and permeability. Pnnint-garinn Prinnin~lp and Prantices of Retrofittina Flood-Prone Residential Structures IV -1 January 1995 Chapter IV: Determination of Hazards ANALYSIS OF FLOOD-RELATED HAZARDS ] The success of any retrofitting measure depends on an accu- I Flood-Related Hazards rate assessment of the flood-related forces acting upon a I structure. Floodwaters surrounding a building exert a num- I Flood Depth I ber of forces on the structure, including lateral and vertical hydrostatic forces, hydrodynamic forces, impact forces, and I Hydrostatic Forces erosion effects. Additionally, interior drainage, closed basin lakes, alluvial fans, and movable bed streamspose flood- Hydrodynamic Forces related hazards that require consideration. I Impact Forces Hydrostatic forces (pressures) are caused by water above the I surface of the ground that is either stagnant or moving slowly. Erosion Hazards Saturated soils beneath the ground surface also impose hydrostatic loads on foundation components. I Interior Drainage I I Hydrodynamic forces (pressures)result from the moderate- Impact loads are imposed on the structure by waterborne Closed Basin Lakes objects; their effects become greater as the velocity of flow, the weight of the objects, and the duration of the impact Movable Bed Streams increase. The basic equations for analyzing and considering these flood-related forces are provided below. I Alluvial Fans or high-velocity flow of water against or around a structure. Figure IV- 1: Flood-Related Haz ards FLOOD DEPTH Riverine Areas The determination of expected flood depth at a site is a Additional information concern-critical aspect of the overall determination of flood-related ing the determination of flood-hazards. One method of determining the 100-yearwater- related forces will be available ir surface elevation is to look at the Flood Insurance Rate Mapthe next revision of the Flood Design Load Criteria incorpo-(FIRM) panel depicting the location of the structure in rated in Section 5 of ASCE 7 question. On most FIRMs, floodplains are delineated for Standard, Minimum Design floods of 100-and 500-year frequencies. As an example, Loadsfor Buildingsand Other Structures, expected to be published in 1995. IV -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Figure IV-2 shows the portion of a community's FIRM where a subject home is located. Figure IV-2: House Location on the FIRM In this example, the location of the home was determined by pacing off the distance from the intersection of Van Nostrand Avenue and Jones Street. The house is located approximately 50 feet north of the intersection. Converting this distance to the map's scale (one inch equals 400 feet), the house is 0.125 inches along Jones Street from its intersection with Van Nostrand Avenue, and 0.125 inches from Jones Street. The darker shaded area on the map is the 100-year floodplain. The lighter shaded area denotes the 500-year floodplain. The house is located in this area between two wavy lines numbered 127 and 128. These are the 100-year flood elevations at those locations on Flat Rock Brook. Therefore, the 100-year flood elevation affecting the home in this example is between 127 and 128 feet, based on the National Geodetic Vertical Datum (NGVD). Flood elevations for the other frequencies are shown on the stream's water-surface profile in the FIS report. For the Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -3 January 1995 Chapter IV: Determination of Hazards above example, the position of the house on Flat Rock Brook was determined by drawing a line on its location on the FIRM (Figure IV-3) perpendicular to the stream. The point where this line crosses the streamline is the location of the house along the stream. \9>1Att l | l | | | | ~~129 \ plied by 400 feet pr ih of m . CESTER ZONE X * X ;EoZONE lSTREET/ \\ xt\\ 2l ~~RM/v 1// Aeu ONE XFla n h Nstr an bridge is a\\Loca thpnon FlnatRc B w w evi \ pointare=126 4 , 25 1 an N \ \12 //S \<\ 128 \ \0--11inhs, \\// tha whe totea \ 124 a meauemn covre 91 Z~~~~ONEX/ _>\ %/ 1 OZONE X s / Figure IV-3: Stream Location on the FIRM The distance along the stream (Figure IV-3) is then measured from the home to Van Nostrand Avenue, the nearest bridge structure across Flat Rock Brook. This distance is 0.1I1 inches, a measurement that when converted to the map scale is equal to approximately 45 feet (0.11 inches multiplied by 400 feet per inch of map). The Van Nostrand Avenue bridge is then located on the Flat Rock Brook profile (Figure IV-4) and measured 0.45 inches upstream (45 divided by 100 feet per inch, which is the horizontal scale of the profile). This location is marked as the point on Flat Rock Brook with water-surface elevations equivalent to the house. The elevations on the profile at this point are 124.5, 125.9, 127.1, and 128.1 feet for the 10-, 50-, 100-, and 500-year floods, respectively. The bottom of the Flat Rock Brook channel shown on the profile is at 119.5 feet. IV -4 EnaineeringPrinciplesand Practices of Ratrofittinn Flooid-Prone Resideantial Structuresa I -vr_**~%-~--^%---._.._ 1995 .*.~~ .z__-aiav. Janluarv 1995 C3-rM CD( _ =y -UIIII o. T CD ci) ~~125 0 - 0 CD I ci) o 120 0 J0> CD 0 (). -L ~i' ILL 115 r 0 -n - 0 0 w~~0 0 CD 0 >0 ------ CD 11 (D 0~~~~~~~~~~~~~~~~~~~~~~~~ Year I (n 0 ~~~~~~~~~~~~~~ 500Flood 2D 0~----~ ---~ ~ ~ ~ ~ 1 0 YearFlood ~~~~~~~~~ D)-----0Y a lo C-- C -------~~~~~~~~Stream C 7.37. . . . Bed .8798081C Stream Distance in Thousands of Feet above Confluence with Overpeck Creek 0L N Chapter IV: Determination of Hazards S~~~~~~~~~~~~~~~~ TableTV-i Flood Data Summary Frequency Elevation Channel 119.5 ft. Bottom 10-yr. 124.5 ft. 50-yr. 125.9 ft. 100-yr. 127.1 ft. 500-yr. 128.1 ft. -r Flood elevations in coastal A and VZones are based on wave height and runup added to the stillwater elevation. For the 1 00-year frequency flood (BFE), refer to the FIRM. For other flood frequencies, the flood elevation can be estimated by multiplying 1.55 times the difference between the stillwater elevation and the ground surface elevation. A detailed discussion of the methodologies involved in computing wave heights and runup is beyond the scope of this manual. Refer to FEMA's Guidelines and Speciflcationsfor Wave Elevation Determination and VZone Mapping, Third Draft, July 1989, for more information. Once the flood frequency and associated elevation information is obtained, a summary table can be created and used to calculate the depth of each flood frequencyto be considered. Table IV-1 depicts the flood data obtained from the FIS for this example Coastal Areas In coastal areas, the determination of the expected water surface elevation for the various recurrence interval floods is made by locating the structure and its flooding source on the FIRM, identifying the corresponding flooding source/ location row on the summary of stillwater elevation table, and selecting the appropriate elevation for the recurrence interval in question. As an example, consider a building located on Georgetown Street (as depicted on Figure IV-5). From the FIRM we can identify the flooding source as the Atlantic Ocean. Review of the entire area map for the FIS would indicate the Town of Fenwick Island (and Georgetown Street) is located between Bethany Beach and the Delaware-Maryland State Line. ZME AE Figure IV-5: Coastal FIRM IV -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 0 0 Analysis of Flood-Related Hazards This flooding source/location is located on the summary of stillwater elevations table (Figure IV-6). From this table, flood elevations of 6.2, 7.8, 8.6, and 10.2 feet above NGVD are identified for the 10-, 50-, 100- and 500-year frequency floods, respectively. Summary of Stillwater Elevations Atantic Ocean Coastline from Cape Henlopen -tojust south-of -DeweyBeach------6.5------8.2------9.2------11.3---- Coastline from just south of Dewey Beach to just north of Bethany Beach 6.4 8.0 8.9 10.8 Coastline from just north of Bethany Beach to Delaware- Maryland state line 6.2 7.8 8.6 10.2 Chesapeake Bay Coastline at Chance 4.2 5.4 5.8 6.8 Delaware Bay Coastline from Kent-Sussex County line to Cape Henlopen 6.6 8.5 9.3 11.3 Indian River Bay Entire coastline 4.7 6.4 7.5 10.8 Rehoboth Bay Entire coastline 3.9 5.9 7.0 10.8 Assawoman Bay Coastline within Sussex County 3.8 5.4 6.0 10.2 Little Assawoman Bay Entire Coastline 3.8 5.4 6.0 10.2 National Geodetic Vertical Datum of 1929 Figure IV-6: Summary of Stillwater Elevations Enaineerina Princinles and Practices of Retrofittina Flood-Prone Residential Structures IV -7 January 1995 Chapter IV: Determination of Hazards I When computing flood depth, be. sure to utilize the lowest ground surface adjacent to the structure in question as shown in Figure IV-7. I Flood depth can be computed by subtracting the lowest ground surface elevation (grade) adjacent to the structure from the flood elevation for each flood frequency, as shown in Formula IV-1. j j d =FE -GS= _feet where: d is the depth of flooding (in feet); FE is the flood elevation for a specific flood frequency (in feet); and GS is the lowest ground surface elevation (grade) adjacent to a structure (in feet). Formula IV- 1: Flood Depth S For design purposes, a factor of safety (freeboard) is typically added to the flood elevation to develop a retrofitting design level as illustrated in Formula IV-2: Flood Protection Elevation. IC-f DI FPE =FE +f = _feet U. where: FPE is the flood protection elevation (in feet); FE is the flood elevation for a specific flood frequency (in feet); and f is the factor of safety (freeboard), typically a minimum of 1.0 foot. Formula IV-2: Flood Protection Elevation The floodproofing design depth (H), which is used to calculate flood-related hazard forces, is the difference between the FPE and the lowest grade adjacent to the structure. This computation is shown in Formula IV-3. v -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards II H=FPE-GS=_feet In some instances involving where: H is the floodproofing design depth combined soil and water forces, over which flood forces are another reference feature such as the top of slab or footing is considered (in feet); normally used instead of lowest FPE is the flood protection elevation adjacent grade to compute the for a specific flood frequency (in floodproofing design depth. feet); and GS is the lowest ground surface elevation (grade) adjacent to the structure (or other reference feature such as a slab or footing) (in feet). Formula IV-3: Floodproofing Design Depth ._ Figure IV-7: Illustration of Flood I)epth and Design Depth Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures IV -9 January 1995 Chapter IV: Determination of Hazards HYDROSTATIC FORCES Hydrostatic Forces Lateral Water Pressures Hydrostatic pressures (loads), at any point of floodwater contact with the structure are equal in all directions and Saturated Soil Pressures always act in a perpendicular manner to the surface on which they are applied. Pressures increase linearly with Combined Water and ] depth or "head" of water above the point under consider- Saturated Soil Pressures ation. The summation of pressures over the surface under Equivalent Hydrostaticconsideration represents the load acting on that surface. Pressures due to Velocity ] For structural analysis, hydrostatic forces, as shown in Figures IV-9 and IV-10, are defined to act: Vertical (Buoyancy) Water Pressures * vertically downward on structural elements such as flat Figure IV-8: Hydrostatic Forces roofs and similar overhead members having a depth of water above them; * vertically upward (uplift) from the underside of generally horizontal members such as slabs, floor diaphragms, and footings (also known as buoyancy); * laterally, in a horizontal direction on walls, piers, and similar vertical surfaces. (For design purposes, this lateral pressure is generally assumed to act on the receiving structure at a point one-third of the water depth above the base of the structure or two-thirds of the altitude from the water surface, which correlates to the center of gravity for a triangular pressure distribution.) Hydrostatic forces include lateral water pressures, saturated soil pressures, combined water and soil pressures, equiva lent hydrostatic pressures due to velocity flows, and vertical or buoyancy pressures. The computation of each of these pressures is illustrated in the sections that follow. For the purpose of this document, it has been assumed that hydrostatic conditions prevail for stillwater and water moving with a velocity of less than ten feet per second. IV -10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards * Flood Protection Elevation | Wm T T T T ti t t Fb: Vertical Upward (Buoyancy)Forces Figure IV-9: Hydrostatic Force Hydrostatic loads generated by velocities up to 10 feet per second may be converted to an equivalent hydrostatic load using the conversion formula presented later in this chapter. Lateral Hydrostatic Forces The basic equation for analyzing the lateral force due to hydrostatic pressure from standing water above the surface of the ground is illustrated in Formula IV-4: Fh =%PhH =2yH2 = lbs/LF where: Fh is the lateral hydrostatic force from standing water (in pounds per linear foot of surface) acting at a distance H/3 from the point under consideration; PhIN is the hydrostatic pressure due to standing water at the point under consideration (in pounds per square foot), (Pl= yH); S is the specific weight of water (62.4 pounds per cubic foot); and H is the floodproofing design depth (in feet). Formula IV-4: Lateral Hydrostatic Forces Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -11 January 1995 Chapter IV: Determination of Hazards Saturated Soil Forces If any portion of the structure is below grade, saturated soil forces must be included in the computation in addition to the hydrostatic force. This situation is illustrated in Figure IV 10.The basic equation for analyzing the resultant lateral force due to hydrostatic forces from saturated (non-expansive) soil is: I-I Fatm=%SDI=% PDD= lb/LF I C0 I -where: Ft is the lateral force from saturated soil acting at a distance D/3 from the point under consideration (in pounds per linear foot of surface); PD is the lateral hydrostatic pressure due to saturated soil at the point Formula IV-5: Saturated Soil under consideration (in pounds Hydrostatic Forces is not suitable per square foot); for expansive soils, due to the unpredictable nature of these S is the equivalent fluid weight of soils. Due to the continual saturated soil (in pounds per cubic shrink and swell of expansive foot); and soil backfills and the variation of D is the depth of saturated soil (in their water content, the stability feet) over which hydrostatic and elevation of these soils and overlaying soil layers may vary forces are considered. considerably. The analysis of hydrostatic pressure and bearing Formula IV-5: Saturated Soil Hydrostatic Forces capacity for expansive soils should be conducted by a qualified soils engineer. Preferably, expansive soils should be removed and replaced by stable soils. IV -12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards W Flood Protection Elevation Figure IV-10: Saturated Soil Hydrostatic Forces The equivalent fluid pressures for various soil types are presented in Tables IV-2 and IV-3. The equivalent fluid weight of saturated soil is not the same as the effective weight of saturated soil. Rather, the equivalent fluid weight of saturated soil is a combination of the unit weight of water and the effective saturated weight of soil. Table IV-2 Effective Equivalent Fluid Weight of Soil(s) Column A Column B S. Equivalent Equivalent Fluid Weight Fluid Weight of Soil Type' ofMoist Soil Submerged (pounds per Soil and cubic foot) Water (pounds per cubic foot) Clean sand and gravel: GW, GP, SW, SP 30 75 Dirty sand and gravel of restricted permeability: 35 77 GM, GM-GP, SM, SM-SP Stiff residual silts and clays, silty fine sands, clayey sands and gravels: CL, ML, CH, MH, SM, 45 82 SC, GC Very soft to soft clay, silty clay, organic silt and 100 106 clay: CL, ML, OL, CH, MH, OH Medium to stiff clay deposited in chunks and 120 142 protected from infiltration: CL, CH Note: See Table IV-3 for soil type definitions. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -13 January 1995 Chapter IV: Determination of Hazards Table IV-3 Soil Type Definitions Based on USDAUnified Soil Classification Soil Type Group Description Symbol Gravels GW Well-graded gravels and gravel mixtures. GP Poorly graded gravel-sand-silt mixtures. GM Silty gravels, gravel-sand-silt mixtures. GC Clayey gravels, gravel-sand-clay mixtures. Sands SW Well-graded sands and gravelly sands. SP Poorly graded sands and gravelly sands. SM Silty sands, poorly graded sand-silt mixtures. SC Clayey sands, poorly graded sand-clay mixtures. Fine Grain Silt ML Inorganic silts and clayey silts. and Clays CL Inorganic clays of low to medium plasticity. OL Organic silts and organic silty clays of low plasticity. MH Inorganic silts, micaceous or fine sands or silts, elastic silts. CH Inorganic clays of high plasticity, fine clays. OH Organic clays of medium to high plasticity. IV -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Combined Water and Saturated Soil Forces When a structure is subject to hydrostatic forces from both saturated soil and standing water (illustrated in Figure IV 11), the resultant cumulative lateral force, FH'is the sum of the lateral water hydrostatic force, Fh, and the differential between the water and soil pressures, F dir The basic equation for computing Fdifis: =D . 5 'foo ' Fdif = 12 (S-y)D2 = _lbsALF where: Fdif is the differential soil/water force acting at a distance D/3 from the point under consideration (in pounds per linear foot of surface); S is the equivalent fluid weight of submerged soil and water (in pounds per cubic foot); D is the depth of saturated soil (in feet); and Y is the specific weight of water (62.4 pounds per cubic foot). Formula IV-6: Combined Water and Soil Forces Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -15 January 1995 ChapterIV: Determination of Hazards 6 FH Fh + FdIf=_ IbsfLF Note that while Fh and Fd1!do not act at the same point, we can where: FH is the cumulative lateral hydro- assume for structural analysis static force acting at a distance purposes that FH acts at a H/3 from the point under considdistance H/3 above the point under consideration. eration (in pounds per linear foot of surface); Fh is the lateral hydrostatic force from standing water (from Formula IV-4); and Fdif is the differential soil/water force (from Formula IV-6). Formula IV-7: Cumulative Lateral Hydrostatic Force V Flood Protection Elevation F~~~~~~~~~~~~F H13 D F~ ~ ~ ~ 7A-Area of F. ~ ~ ~ ~ ~ ~ ~ ~ ~ ,~ H orizontal D~~~~~ F ~~~Surf ace T t FbT t t t Figure IV-I 1: Combination Soil/Water Hydrostatic and Buoyancy Forces IV -16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Vertical Hydrostatic Force The basic equation for analyzing the vertical hydrostatic force (buoyancy) due to standing water (illustrated by Figure IV-l 1.) is: F=~~~~~b yAH= lbs where: Fb is the force due to buoyancy (in pounds); Y is the specific weight of water (62.4 pounds per cubic foot); A is the area of horizontal surface (floor or slab) being acted upon (in square feet); and H is the floodproofing design depth (in feet). Formula IV-8: Buoyancy Force The computation of hydrostatic forces is vital to the successful design of floodwalls, sealants, closures, shields, foundation walls, and a variety of other retrofitting measures. The following Hydrostatic Force Computation Worksheet (Figure IV- 12) can be utilized to conduct hydrostatic calculations. Figure IV- 13, Example Hydrostatic Force Computation, illustrates the use of the worksheet. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Iv -17 January 1995 HYDROSTATIC FORCE COMPUTATIONWORKSHEET Owner Name: Prepared By: Address: Date:_ Property Location: Variables: Summary ofForces H (Floodproofing Design Depth)= Fh= D (Depth of Saturated Soil) = Fsat= y (Specific Weight of Water) = 62.4 lbs/cubic foot Fdif= S (Equivalent Fluid Weight of Saturated Soil) = FH= A (Area) = Fb= Formula IV-4: Lateral Hydrostatic Force From Freestanding Water Fh =%PhH = %yH2= Formula IV-5: Lateral Hydrostatic Force From Saturated Soil Fsat = S D2or %PDD= Formula IV- 6: Lateral Hydrostatic Force From Standing Water and Saturated Soil Fdif= I/ (S-y) D2 Formula IV-7: Total Lateral Hydrostatic Force From Standing Water and Saturated Soil FH= Fh+ Fddf Formula IV-8: Vertical Hydrostatic Force (Buoyancy) Fb= yA = Note: Formulas IV-4-6 do not account for equivalent hydrostatic loads due to velocity floodwaters (less than 10 fps.). If velocity floodwaters exist, recompute FH using Formula IV- 11. Figure IV- 12: Hydrostatic Force Computation Worksheet IV- 18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards i HYDROSTATIC FORCE COMPUTATION WORKSHEET I Owner Name: 5t WMt Prepared By: -=V Address: m 1S Date: 3i lZy mier 1e l'et PropertyLocation: 7M 3I 9S lcnots 4. L-arrLA Variables: Summary of Forces H (Floodproofing Design Depth)= *Fh= LA9"1 bI LP D (Depth of Saturated Soil) = Z F, t= tio > kipsIL y (Specific Weight of Water) = 62.4 lbs/cubicfoot Fdi = l ° \ \t 1LF S (Equivalent Fluid Weight of Saturated Soil) = AFH= 6C> 1\s ILP A(Area)= Mentor*-lucO-:5 4 F, Z9c,5ZCD %U5 Formula IV-4: Lateral Hydrostatic Force From Freestanding Water Fh=VZPH = Vr/W =/*Xi4(i.4 Q) k99 ls Lp Formula IV-5: Lateral Hydrostatic Force From Saturated Soil F= I/D ( V)L -as 2 SD= Lo/4)(z t\'O I/LF Formula IV-6: Lateral Hydrostatic Force From Standing Water and Saturated Soil Fdif= 1 (S-)D = YL&4SE;-ZI'i 1h44Q(L (L 4) -\ O \ t5 /L5 Formula IV-7: Total Lateral Hydrostatic Force From Standing Water and Saturated Soil FH= Fh+ Fd;= 4991 16LrF * jot I/L H ~~ ~ ~ ~ F. ~ ~ i.~ ~ .. ... I Formula IV-8: Vertical Hydrostatic Force (Buoyancy) I Fb=yAH= (•4-Li 4as)(20O0OeX'4 &) -z2,sqo 1IS 8s Note: Formulas IV-4-6 do not account for equivalent hydrostatic loads due to velocity floodwaters (less than 10 fps.). If velocity floodwaters exist, recompute F. using Formula IV-1 1. I J Figure IV-13: Example Hydrostatic Force Computation Worksheet Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV-19 January 1995 Chapter IV: Determination of Hazards HYDRODYNAMIC FORCES When floodwaters flow around a structure at moderate to high velocities, they impose additional loads on the structure, as shown in Figure IV- 14. These loads consist of frontal impact by the mass of moving water against the projected width and height of the obstruction represented by the structure, drag effect along the sides of the structure, and eddies or negative pressures on the downstream side of the structure. Low velocity hydrodynamic forces are defined as situations where floodwater velocities do not exceed 10 feet per second, while high velocity hydrodynamic forces involve floodwater velocities in excess of 10 feet per second. Negative Pressure (Suction) on DownstreamSide w 0 Drag Effect on Sides Figure IV-14: Hydrodynamic and Impact Forces IV -20 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Sources of data for determining flood flow velocity include hydraulic calculations, historical measurements, and rules of thumb. Floodwaters one foot deep moving in excess of five feet per second can knock an adult over and cause erosion of stream banks. Overbank velocities are usually less than stream channel velocities. If no data for flood flow velocity exists for a site, the reader should contact an experienced hydrologist or hydraulic engineer for estimates. Table IV-4 Drag Coefficients Width to height Drag Coefficient Ratio b/h Cd From 1 to 12 1.25 13 to 20 1.3 21 to 32 1.4 33 to 40 1.5 41 to 80 1.75 81 to 120 1.8 160 or more 2.0 Low Velocity Hydrodynamic Forces In cases where velocities do not exceed 10 feet per second, the hydrodynamic effects of moving water can be converted to an equivalent hydrostatic forceby increasing the depth of the water (head) above the flood level by an amount dh, which is: dh-CdV2 =_feet 2g where: dh is the equivalent head due to low velocity flood flows (in feet); Cd is the drag coefficient (from Table IV-4); V is the velocity of floodwaters (in ft/sec); and g is the acceleration of gravity (equal to 32.2 ft/sec2). Formula IV-9: Conversion of Low Velocity Flow to Equivalent Head The drag coefficient Cddepends on the proportions of the shape of the object around which the water flows. The value of Cd,unless otherwise evaluated, shall not be less than 1.25 and can be determined from the width-to-height ratio, b/h, of the structure in question. The width (b) is the side perpendicular to the flow and the height (h) is the distance from the bottom of the structure to the water level. Table IV-4 gives Cdvalues for different width-to-heightratios. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -21 January 1995 Chapter IV: Determination of Hazards The value dh is then converted to an equivalent hydrostatic pressure through use of the basic equation for lateral hydrostatic forces introduced earlier in this chapter and modified as shown below: I-II IDco li Fdh= y (dh)H = PdhH = lbs/LF where: Fdh is the equivalent hydrostatic force due to low velocity flood flows (in pounds per linear foot of surface); Y is the specific weight of water (62.4 pounds); H is the floodproofing design depth in feet; dh is the equivalent head due to low velocity flood flows in feet; and Pdh is the hydrostatic pressure due to low velocity flood flows (in pounds per square foot) (Pdh = y (dh)). Formula IV-10: Conversion of Equivalent Head to Equivalent Hydrostatic Force The resultant lateral hydrostatic force due to low velocity hydrodynamic pressures is then added to the lateral hydrostatic pressures due to standing water and saturated soil to obtain the total lateral hydrostatic force shown below and A-' While Fdh acts at a point H/2, it is normally a small percentage of FH,therefore, we can assume that Fdh acts at the same point H13 as FH. illustrated in the Equivalent Hydrostatic Force Computation Worksheet, Figures IV-15 and IV-16. DCD D FH Fh +F. +Fd lbsILF H h dif dh where: variables were defined previously in Formulas IV-4, IV-6, IV-7, and IV-lO. Formula IV- 11: Total Lateral Hydrostatic Force IV -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related: Hazards EQUIVALENT HYDROSTATIC FORCE COMPUTATION WORKSHEET Owner Name: -Prepared By: Address: _ Date: Property Location: Variables: Summary of Forces b (width of structure perpendicular to flow) = Fdh= = H (floodproofing design depth) = Fh h (height of water above structure bottom) = Fdif= V (velocity of flood water, 10 feet per second or less) = F = y (specific weight of water) = 62.4 lbs/cubic foot g (acceleration of gravity) = 32.2 feet per second squared Formula IV-9: Conversion of Low Velocity Flood Flow to Equivalent Head dh== Cd'V2 2g Develop Cd: b/h = From Table IV-4; Cd= Formula IV-10: Conversion of dh to Equivalent Hydrostatic Force Fdh= Y(dh)H= Formula IV-l 1: Total Lateral Hydrostatic Force FH = Fh+Fdif +Fdh= Figure IV-15: Equivalent Hydrostatic Force Computation Worksheet Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -23 January 1995 ChapterIV: Determination of Hazards EQUIVALENTHYDROSTATICFORCE COMPUTATIONWORKSHEET OwnerName: vA . Prepared By: --f Address: v. W^r 5-rM*r Date: to1l idl PropertyLocation:-rM 3 , LcT LA So nom 6 Variables: Summary of Forces b (width of structure perpendicular to flow)= 3° Fdb = i I LF H(floodproofingdesigndepth)=4' Fh= '499 1bfLF h(heightofwaterabovestructurebottom)= F.,= 1I s/L 3 lto t V (velocity of flood water, 10 feet per second or less) = = -415 ls ILF y (specific weight of water) = 62.4 lbs/cubic foot g (acceleration of gravity) = 32.2 feet per second squared Formula IV-9: Conversion of Low Velocity Flood Flow to Equivalent Head CdV2 dh = 2 = 2g /NS \Develop Cd: _____)____ b/h= 10 z C3ZZ iSec) FromTab1elV-4;Cd=1.Z5 OA-Q+ --ze Formula IV-10: Conversion of dh to Equivalent Hydrostatic Force Fdh y(dh)H= C(z1 &A * .- 45 16s/ur Formula IV-l 1: Total Lateral Hydrostatic Force FH= Fh+ Fdir+ Fdh= L499 +41014+ 5 jlos/LF : Hyrti Fc C/LF Figure IV-16: Example Equivalent Hydrostatic Force Computation IV -24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards HIGH VELOCITY HYDRODYNAMIC FORCES For special structures and conditions, and for velocities greater than 10 feet per second, a more detailed analysis and evaluation should be made utilizing basic concepts of fluid mechanics and/or hydraulic models. The basic equation for hydrodynamic pressure is: v 2 : -lbs/SF CdP =d where: Pd is the hydrodynamic pressure (in pounds per square foot); p is the mass density of water (1.94 slugs/ft3 ); V is velocity of floodwater (in feet per second); and Cd is the drag coefficient (taken from Table IV-4). Formula IV-12: High Velocity Hydrodynamic Pressure After determination of the hydrodynamic pressure (Pd)' the total force (Fd)against the structure (see Figure IV-14) can be computed as the pressure times the area over which the water is impacting: F =P A-lbs ails ~~~~dd where: Fd is the total force against the structure (in pounds); Pd is the hydrodynamic pressure (in pounds per square foot); and A is the submerged area of the upstream face of the structure in question (in square feet). Formula IV-13: Total Hydrodynamic Force ln,.mn~pinjn Drineidnle and Practices of Retrofittinn Flood-ProneResidentialStructures IV-25 Januarv 1995 Chapter IV: Determination of Hazards Figure IV- 17,Hydrodynamic Force (High Velocity) Computation Worksheet, can be used in the computation of high velocity hydrodynamic forces, while Figure IV-18 illustrates the computations. IV -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards HYDRODYNAMIC FORCE (HIGH VELOCITY) COMPUTATIONWORKSHEET Owner Name: Prepared By: Address: Date:_ Property Location: Variables: Summary of Forces p (mass density of water) = 1.94 slugs/ft3 Pd = V (velocity of floodwater, > 10 feet per second) Fd= Cd(drag coefficient) = A (submerged area of upstream face of structure) = Formula IV-12: High Velocity Hydrodynamic Pressure (Force) Pd =Cdp (VI/ 2) Develop Cd. b/h = From Table IV-4; Cd= Formula IV-13: Total Force Against the Structure Fd = Pd A= M Figure IV-17: Hydrodynamic Force (High Velocity) Computation Worksheet Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IVIV-27 January 1995 Chapter IV: Determination of Hazards HYDRODYNAMICFORCE (HIGH VELOCITY) COMPUTATION WORKSHEET OwnerName: 5 *AI vA Prepared By: Address: v12 UJAr-'R dSeT Date: Loe:I 19'4 PropertyLocation::TrN 313, 5cro% N (a. LOT 4 Variables: Summary ofForces p (mass density of water) = 1.94 slugs/ft3 Pd= I5 9 1H V (velocity of floodwater, >10 feet per second) = 12.' 5 Fd= 2 I, C UP5 Cd(drag coefficient) =I, Z 5 A (submerged area of upstream face of sttucture) = l _ I2 O ___ a Formula IV-12: High Velocity Hydrodynamic Pressure (Force) Pd=Cdp (W 2)= 1.94 Sft ~~Z Develop Cd: a1.5( 1yg-b/h = iJ" 5u 7 A From Table IV-4; Cd= l.ZY sh -~ ~ ~~Z lb same Fonnula IV-13: Total Force Against the Structure Fd= d A= (V \+frr")C a 4 ) Fu& L 00 \1 E Figure IV-I 8: Example Hydrodynamic Force (High Velocity) Computation IV -28 Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards IMPACT LOADS Impact loads are imposed on the structure by objects carried by the moving water. These loads are the most difficult to predict and define, yet reasonable allowances must be made for these loads in the design of retrofitting measures for potentially affected buildings. To arrive at a realistic allowance, considerablejudgment must be used, along with the designer's knowledge of debris problems at the site and consideration of the degree of exposure of the structure. Impact loads are classified as either: * no impact (for areas of little or no velocity or potential source of debris); * normal impact; * special impact; or * extremeimpact. Engineerina Principles and Practices ol Retrofitting Flood-Prone Residential Structures IV -29 January 1995 Chapter IV: Determination of Hazards Normal Impact Forces Normal impact forces relate to isolated occurrences of typically sized ice blocks, logs, or floating objects striking the structure (see Figure IV-14). For design purposes, this can be considered a concentrated load acting horizontally at the flood elevation, or any point below it, equal to the impact force created by a 1,000-pound mass traveling at the velocity of the floodwater acting on a one-square-foot surface of the submerged structure area perpendicular to the flow. The calculationof normal impact forces is shown in Formula IV-14. Li = MV =W~V -F lbs F _= gt where: Fn is the normal impact force (in pounds); wn is weight of object (1,000 lbs for normal impact loads); g is acceleration of gravity (32.2 ft/ sec 2); t is time of impact (generally 1 sec or less); V is velocity of flow (in feet per second); and M is the mass of the object computed as w.Ig. Formula IV-14: Normal Impact Force IV -30 Enqineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Special Impact Forces Special impact forces occur when large objects or conglom erates of floating objects, such as ice floes or accumulations of floating debris, strike a structure. In an area where special impact forces may occur, the load considered for design purposes is the impact created by a 1 00-pound load times the width of building, acting horizontally over a one- foot-wide horizontal strip at the flood elevation or at any level below it. Where stable natural or artificial barriers exist that would effectively prevent these special impact forces from occurring, these forces may not need to be considered in the design. E MV wV 1OObV u lullFS= t gt 32. 2t where: F. is the special impact force (in pounds); Ws is weight of object (in pounds) (100 lbs/ft x width of structure (b) normal to flow); b is shown in Figure IV-14; b is the width of structure normal to flow (in feet); g is acceleration of gravity (32.2 ftlsec2); t is time of impact (generally 1 sec or less); V is velocity of flow (in feet per second); and M is the mass of the object computed as w/g I Formula IV-15: Special Impact Forces IV -31 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ; ~~IV-31 January 1995 /iI-- Chapter IV: Determination of Hazards Whether impact loads should be allowed for depends on data that can be obtained from a number of sources: * historic records and the FIS; * interviewswith local residents and floodplain management officials; * floodway versus floodplain location; * upstream debris potential; and * climatologic information. Impact forces are critical design considerations that must be thoroughly evaluated. The following Impact Force Computation Worksheet, Figure IV-19, can be used to conduct those calculations, while Figure IV-20 illustrates those calcu lations. Extreme Impact Forces Extreme impact forces occur when large, floating objects and Where extreme impact loads are a threat, the preferred retrofitting masses, such as runaway barges or collapsed buildings andalternativeis relocation. structures, strike the structure (or a component of the structure). These forces generally occur within the floodway or areas of the floodplain that experience the highest velocity flows. It is impractical to design residential buildings to have adequate strength to resist extreme impact forces. IV -32 EnaineerinoPrinrinlss andiPractices nf Pctrnfittiret Flnnnrl-Dr-nc -;A.-s.-.+;:IC0+,. I¢>ttLICu --4, -->--a ,r--. . IILII.IlJ_41 a -{icazl~iyEvuc-iul 'JLIUL.LUrIe January 1995 Analysis of Flood-Related Hazards IMPACT FORCE COMPUTATION WORKSHEET Owner Name: Prepared By: Address: Date: Property Location: Normal Impact Loads Variables: Summary of Forces w. (weight of object) = typically, 1,000 pounds g (acceleration of gravity) = 32.2 ft/sec2 F = t (time of impact) = typically, 1sec. F,= V (velocity of floodwater)= M (mass of the object computed as wjIg) Formula IV-14: Normal Impact Force F MV wV n t = gt Special Impact Loads Variables: b (width of structure normal to flow) = w, (weight of object) = 100 (b) = g (acceleration of gravity) = 32.2 ft/sec2 t (time of impact) = typically, 1 sec. or less V (velocity of floodwater)= M (mass of the object computed as wIg) = Formula IV- 15: Special Impact Forces MV w5V 100bV F =-=-t gt 32.2t = -lbI=s Figure IV-19: Impact Force Computation Worksheet Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures IV -33 January 1995 Chapter IV: Determination of Hazards IMPACT FORCE COMPUTATION WORKSHEET Owner Name: 5 M t'r-* Prepared By: TeV Address: z W4-mr-tSM-rET Date: 10131 IIS PropertyLocation: , 38 Sec-o' , Normal Impact Loads Variables: Summaryof Forces wn (weight of object) = typically, 1,000 pounds g (acceleration of gravity) = 32.2 ft/sec2 F = 3-r3 IL5 t (time of impact) = typically, 1 sec. FJ= kleti V (velocityoffloodwater)= I% l t M (massof the object computed as wj/g)=3- Formula IV-14: Normal Impact Force FWnV(l$o Z*+fB s3 \5( n. t t CS Z. Z + 4j t t sc t~~ 343\ Special Impact Loads Variables: b (width of structure normal to flow) = 3 w1 (weightofobject) = = lac (so I00(b) o 4(30 3000+ g (acceleration of gravity) = 32.2 ft/sec2 t (time of impact) = typically, 1 sec. or less V (velocityof floodwater) = t1 -BD M (mass of the object computed as wig)-= ° '/iz.Z -E4/1 J Formula IV-15: Special Impact Forces M w,V =lObV _(lo it(4)(0 &1)CLJ.I~sa*) 5igure Example m32.2t Fc Czmp at I -sc) ;eisure IV-20: Example Impact Force Computation IV -34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards RIVERINE EROSION The analysis of erosion that impacts stream banks and nearby overbank structures is a detailed effort that is usually accompanied by detailed geotechnical investigations. Some of the variables that impact the stability (or erodibility) of the stream banks include the following: * critical height of the slope; * inclination of the slope; * cohesive strength of the soil in the slope; * distance of the structure in question from the shoulder of the stream bank; * degree of stabilization of the surface of the slope; * level and variation of groundwater within the slope; * level and variation in level of water on the toe of the slope; * tractive shear stress of the soil; and * frequency of rise and fall of the surface of the stream. Both FEMA and the USACE have researched the stability of stream banks in an effort to quantify stream bank erosion. However, concerns over the universal applicability of the research results preclude their inclusion in this manual. It is suggested that when dealing with streambanks susceptible to severe erosion, the designer contact a qualified geotechnical engineer or a hydraulic engineer experienced in channel stability. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -35 January 1995 S Chapter IV: Determination of Hazards i Rainfall intensities f or the eastern half of the United States are available from H'YDRO-35,a publication of the N; ational Weather Service (NAVS),while rainfall intensities fe ir aet western half of the L can be obtained fromi NOAA ATLAS 2, also publis shed by the NWS. Rainfall interisitiesare available for a range of storm frequencies including ;the 2-, 10-, 25-, 50-, and 100-year 60minute events. The:2- or 10- year intensity rainfalI is consid- ered a minimum desi for pumping rates wiienflood- waters prevent gravity discharge from floodwalls and levees.The 100-year intensity rainfall should be the maximum design value for sizing gravit' flowpipes and/or closures The rational formula (Q=cirA) is used to compute the amount of precipitation runoff from small areas. It is generally not applicable to drainage areas greater than 10 acres in size. INTERIOR DRAINAGE The drainage system for the area enclosed by a levee or floodwall must accommodate the precipitation runoff from this interior area (and any contributing areas such as roofs and higher ground parcels) and the anticipated seepage through or under the floodwall or levee during flooding conditions. There are two general methods for removing interior drainage. The first is a gravity flow system, which provides a means for interior drainage of the protected area when there is no floodwater against the floodwall or levee. This is accomplished by placing a pipe(s) through the floodwall or levee with a flap gate attachment. The flap gate prevents flow from entering the interior area through the drainpipe when floodwaters rise above the elevation of the drain. The second method, a pump system, removes accumulation of water when the elevation of the floodwater exceeds the elevation of the gravity drain system. A collection systemcomposed of pervious trenches, underground tiles, or sloped surface areas transports the accumulating water to a sump area. In the levee application, these drains should be incorporated into the collection system. The anticipated seepage from under and through levees and floodwalls must also be taken into consideration by combining it with flow from precipitation (see Figure IV-2 1). Floodwallor Levee House J~s Enclosed Y 1 C Area An=(x)(y) I~~~~~~~~Ix .1 RectangularArea FigureIV-2 1: Figure IV-2 !: Rectangular Area Enclosed by a Floodwall or Levee IV -36 Engineering Principles and Practices of Retrofittino Flood-Prone ResideontialStruiicture Januarv 1995 Analysis of Flood-Related Hazards 6 The residential terrain runoff coefficient, c, is used to model the runoff characteristics of different land uses. Use the value for the predominant land use within a specific area or develop a weighted average for areas with multiple land uses. The most common coefficients are 0.70 for residential area, 0.90, for commercial area, and 0.40 for undeveloped land. Figure IV-22: Rectangular Area Partiall: y Enclosed by a Floodwall or Levw To determine the amount of precipitation that can collect in the contained area, the rainfall intensity, given in inches per hour, must be determined for a particular location (see note). This value is multiplied by the enclosed area, Aa, in square feet, a residential terrain runoff coefficient (c) of 0.7, and a conversion factor of 0.01. The answer is given in gallons per minute. mmU U Qa= 0U01 cir Aa= gpm where: Q. is the runoff from the enclosed area (in gal/min (gpm)); Aa is the area enclosed by the floodwall or levee (in square feet); c is a residential terrain runoff coefficient of 0.7; 0.01 is a factor converting the answer to gallons per minute; and ir is the intensity of rainfall (in inches per hour). Formula IV-16: Runoff Quantity in an Enclosed Area In some cases, a levee or floodwall may extend only partially around the property and tie into higher ground (see Figure IV-22). For such cases, the amount of precipitation that can flow downhill as runoff into the protected area, A., must be included. To calculate this value, the additional area of land, Abl that can discharge water into the enclosure should be estimated. This value is then multiplied by the previously determined rainfall intensity, ir,by the most suitable terrain coefficient, and by 0.01. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -37 January 1995 Chapter IV: Determination of Hazards When determining the minimum discharge size for sump pumps within enclosed areas, the designer should consider the impacts of lag time between storms that control the gravity flow mechanism (i.e., inside and outside the enclosed area) and the storage capacity within the enclosed area after the gravity discharge system closes. If the designer is not familiar with storm lag time and the computation of storage within an enclosed area, an experienced hydrologist or hydraulic engineer should be consulted. _ojI Inc D w er Qb =001 CirAb = gpm where: Q1b is the runoff from additional contributing area (in gal/min (gpm)); Ab is the area discharging to the area partially enclosedby the floodwall or levee (in square feet); c is the most suitable terrain runoff coefficient; 0.01 is a factor converting the answer to gallons per minute; and ir is the intensity of rainfall (in inches per hour). Formula TV-17: Runoff Quantity from Higher Ground into a Partially Enclosed Area Seepage flow rates from the levee or floodwall, Q, must also be estimated. In general, unless this seepage rate is calculated by a qualified soils engineer, a value of two gallonsper minute for every 300 feet of levee or one gallon per minute for every 300 feet of floodwall should be assumed during base 100-year-floodconditions. I wr QC= sr(l) where: QC is the seepage rate through the levee/floodwall (in gallonsper minute); sr is the seepage rate (in gallons per minute) per foot of levee/floodwall; and I is the length of the levee/floodwall (in feet). Formula IV-18: Seepage Flow Rate through a Levee or Floodwall IV -38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards The values for inflow within the enclosed area, runoff from uphill areas draining into the enclosure, and seepage through the levee/floodwall should be added together to obtain the minimum discharge size, Q5,Pin gallons per minute (gpm) for the sump pump. I_ imgwr Qp= Q +Qb+ Q where: QSp is the minimum discharge for sump pump installation (in gpm); Q. is discharge from an enclosed area (from Formula IV-16) (gpm); Qb is the discharge from higher ground to a partially enclosed area (from Formula IV- 17) (in gpm); and Q, is the discharge from seepage through a floodwall or levee (from Formula IV- 18) (in gpm). Formula IV-19: Minimum Discharge for Sump Pump Installation Important considerations in determining the minimum discharge size of a sump pump include storage available within the enclosed area and the lag time between storms that impact the enclosed area and the area to which the enclosed area drains. Sump pumps will continue to operate during flooding events (assuming power is constant or backup power is available), but gravity drains will close once the floodwater elevation outside of the enclosed area exceeds the elevation of the drain pipe/flap gate. Therefore, the critical design issue is to determine runoff and seepage that occurs once the flap gate closes. Typical design solutions incorporate a freeboard of several inches or more to control the 10-year flood event safely. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -39 January 1995 Chapter IV: Determination of Hazards ALLUVIAL FAN FLOODING HAZARDS Alluvial fan floods are natural hazards in the western A detailed discussion of alluvial United States. Alluvial fan flooding is characterized by fan flooding and techniques for sudden unpredictable, high-velocity flow that transports retrofittingunder those conditions dangerous debris down steep mountain drainages to the is presented in Appendix D: valley floor below. The type of detailed information avail- I AlluvialFan Flooding. able for other flood-prone areas is not yet available for alluvial fan situations, but a profile of this type of flooding and general measures to mitigate its impacts are beginning to emerge. Alluvial fans are landforms evolved from a history of flood events debouching from steep-sloped watersheds onto valley floors or piedmonts. Across the western United .00* States alluvial fans are appealing to residential developers for their vistas, and the pressure to construct on fans is Alluvial Fans: Hazards and increasing as the valley floors become populated. On most Management (1989) is a FEMA fans, there is evidence of past floods, but the history of publication that provides an overview of alluvial fans and development is relatively short and the consequences of a related management issues, and 1 00-year return period flood may not have been fully briefly discusses retrofitting of addressed. residential structures. Another FEMA publication entitled Reducing Losses in High Risk Flood Hazard Areas: A Guidebookfor Local Officials specifically addresses alluvial fan flooding as a regulatory problem and provides outlines for the development of regulations and master plans for communities. This guidebook also summarizes the Dawdy Method for flood frequency estimates on alluvial fans and presents the Colorado Statute HB-1041 as a model geologic hazard ordinance that includes alluvial fan flooding . hazards. Figure IV-23: Telluride, Colorado, Alluvial Fan IV -40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Flood hazards on alluvial fans are compounded by high velocities, hyper-concentrated sediment flows, severe erosion, and massive sediment deposition. Retrofitting designs are typically dependent on the assessment of flood hazards (specifically flow depth and velocity), but for alluvial fans this information may not be available. FIRMs may provide general information such as the delineation of flood hazard zones and 1 00-year maximum flow depths. Local ordinances may recommend methods for determining design criteria. Additional available information may include the apex peak discharge and potential sediment concentrations. Retaining a qualified engineer may be necessary to determine design flow conditions at the property location. Some aspects of alluvial fan flood loads are comparable to riverine flooding. Flow analyses including hydraulic loading and buoyancy are similar in principle to riverine flooding, but several key elements are different. Alluvial fan analyses should consider the severe velocity gradients, the combined effects of water and sediment mixtures, boulder impact pressure, and hydraulic loading on the upstream side of a structure. Formulas for the computation of sediment-water mixtures, hydrodynamic forces, freeboard, and factor of safety recommendations are provided below. Bulking Factor The design flood conditions must be evaluated considering the increased flood discharge related to sediment bulking. The bulking factor, BF, is given by Formula IV-20. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -41 January 1995 Chapter IV: Determination of Hazards [ 11l1 1_ JE l BF ~~~~~~~~~~~~~~~~~~1. Concentration of Sediment (C,) values are estimated by engi- neers experienced with this type of analysis and typically range from 0-50% (decimal equiva- lent). 1_________________________ In hyperconcentrated sediment flows,. where the sediment concentrations range from 20 to 45 percent sediment by volume, the hydrostatic pressurescan be 30 to 75 percent greater than from clear water. 1.0 BF = 0- C, is a dimensionless factor applied to riverine discharge values (Q) to account for sediment bulking; and is the concentration of sediment of the fluid mixture by percent (decimal equivalent) of volume. where: BF Cv Formula IV-20: Bulking Factor For semi-arid alluvial fans, typical bulking factors range from 1.1 to 1.2 for sediment concentrations of 0.10 to 0.15 by volume. Bulking factors for mud flows can be as high as 2.0 (C = 0.50). Hydrostatic and Hydrodynamic Loads Hydrostatic loading is the force of the weight of standing water acting in a perpendicular manner on a submerged surface Sediment suspended in floodwater will increase the specific weight of the fluid as a function of sediment concentration by volume C,. Water with a high sediment concentration will impose greater hydrostatic pressures than clear water. Likewise, hydrodynamic loading is related to the density of the fluid, which will increase with sediment loading. The greater mass the fluid has, the more momentum it will transfer when it impinges on an obstacle. To include the effects of sediment loading in hydrostatic and hydrodynamic calculations, the specific weight of water is replaced with the specific weight of the water-sediment mixture (Formula IV-21). IV -42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards -It' In alluvial fan situations, hydrostatic and hydrodynamic forces developed using Formulas IV-4 through IV- 13 should be recomputed replacing the specific weight of water (y ) with the specific weight of the water- sediment mixture (y,). ffi!1 Ys= (1-C)y + cSSP y= __lbs/ft3 where: ys is the specific weight of the water-sediment mixture, in lbs/ft3 ; C, is the sediment concentration by volume expressed as a percent (decimal equivalent); y is the specific weight of water, 62.4 lbs/ft3 ; and SP is the specific gravity of sediment (dimensionless). Formula IV-21: Specific Weight of Water-Sediment Mixture The additional live load attributed to sediment should be considered in all calculations of hydrostatic loading with volumetric concentration of five percent or greater. This additional hydrostatic load will be most significant near the fan apex where sediment concentrations are higher and will decrease in the downfan direction. The loading factor related to sediment will be negligible in the sheet flow zone. Freeboard Prediction of alluvial fan flooding parameters is not an exact science, so safety factors should be considered in retrofitting design. Freeboard is the additional design height of walls, levees, and foundations above the base flood level to account for velocity head, waves, splashes, and surges. The conditions of superelevation and flow runup can be severe for mud, debris, and high velocity flows and should be evaluated separately. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -43 January 1995 Chapter IV: Determination of Hazards The U.S. Army Corps of Engineers recommends that the freeboard () be greater than or equal to 2.0 feet in alluvial fan situations. Hydrostatic, hydrodynamic, and impact loading design should fall within constraints imposed by local ordinances or building codes. Where local guidelines are not available, factors of safety pre sented in Table IV-5 should be applied to design loads for structure design. The U.S. Army Corps of Engineers (draft report, undated) recommends that the amount of freeboard be based on the velocity head plus the increase in depth caused by a 50% increase in flow rate, with a minimum value of 0.5 feet, expressed by the equation shown in Formula IV-22: MEE,.3 5f = |disQdesign-dQdesign)+ V2/2g= ft where: f V g is the recommended freeboard in feet; is the velocity of flow in feet per second; is the acceleration of gravity (32.2 ftlsec2 ); d SQdesignis the depth of flooding from a discharge 50% greater than the design discharge, in feet; and dQdifgnis the depth of flooding from the design discharge (typically the 1 00-year event), in feet. Formula IV-22: Recommended Freeboard Safety Factors A safety factor greater than one is an additional measure of safety to account for unanticipated or unquantifiable factors. In the case of retrofitting on alluvial fans, additional safety should be built into the design, depending on the engineer's perception of the sensitivity of the flow conditions to change. The engineer must also weigh the cost of obsolescence if a retrofitting technique becomes inadequate with continued development. Safety factors are always a compromise between the desire for added protection and the additional costs associated with retrofitting design and construction. IV -44 Engineering Principlesand Practicesof Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards Table IV-5 Freeboard and Factor of Safety Recommendations Type of Flooding Type of Flooding Shallow Water Flooding, < 1 ft. (FIRM Zones A andB) Wtr____<3f.12 Freeboard ~~(ft.) 1 Factor of Safety 1.10 Moderate Water Flooding, < 3 ft. 1 1.20 Moderate Water Flooding, < 3 ft. with potential debris, rocks < 1 ft. diameter and sediment for 1 1.20 Mud Floods, Debris Flooding < 3 ft., minor surging and deposition, < 1 ft. boulders 2 1.25 Mud Flows, Debris Flows < 3 ft., surging, mud levees, > 1 ft. boulders, minor waves, deposition 2 1.40 Mud and Debris Flows > 3 ft., surging, waves, boulders > 3 ft., major deposition 3 1.50 Source: 1986 Colorado Floodproofing manual Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -45 January 1995 / 49mlbi' Chapter IV: Determination of Hazards CLOSED BASIN LAKES Two types of lakes pose special hazards to adjacent devel- More information on closed basin opment: lakes with no outlets, such as the Great Salt Lake lakes, alluvial fan, and movable and the Salton Sea (California); and lakes with inadequate, bed stream hazards can be obtainedfromthe Community or elevated outlets, such as the Great Lakes and many Rating System (CRS)Commen-glacial lakes. These two types are referred to as "closed tarySupplementfor Special basin lakes." Closed basin lakes are subject to very large Hazards Credit, dated July 1994. fluctuations in elevation and can retain persistent high water This document is available 1v1 through Flood Publications, evels. NFIP/CRS, P.O. Box 501016, Indianapolis,Indiana46250-Closed basin lakes occur in almost every part of the United 10 16. Telephone (317) 845-2898. States for a variety of reasons: lakes in the northern tier of states and Alaska were scoured out by glaciers; lakes with no outlets (playas) formed in the west due to tectonic action; oxbow lakes along the Mississippi and other large rivers formed as a result of channel migration; and sinkhole lakes form in areas with large limestone deposits at or near the surface where there is adequate surface water and rainfall to dissolve the limestone (Karst topography). Determination of the flood elevations for closed basin lakes follows generally accepted hydrological methods, which incorporate statistical data, historical high water mark determinations, stage-frequency analysis, topographical analysis, water balance analysis, and combinations of these methods. While NFIP regulations do not specifically address closed basin lakes, communities that develop mapping and regulatory standards addressing these hazards may receive flood insurance premium credits through the NFIP Community Rating System. The designer should determine if a local community has mapped or enacted an ordinance covering this special hazard. IV -46 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Flood-Related Hazards MOVABLE BED STREAMS Erosion and sedimentation are factors in the delineation and regulation of almost all riverine floodplains. In many rivers and streams, these processes are relatively predictable and steady. In other streams, sedimentation and erosion are continual processes, often having a larger impact on the extent of flooding and flood damages than the peak flow. Extreme cases of sedimentation and erosion are a result of both natural and engineered processes. They frequently occur in the arid west, where relatively recent tectonic activity has left steep slopes, where rainfall and streamrflow are infrequent, and where recent and rapid development has disturbed the natural processes of sediment production and transport. Movable bed streams include streams where erosion (degradation of the streambed), sedimentation (aggradation of the streambed), or channel migration cause a change in the topography of the stream sufficient to change the flood elevation or the delineation of the floodplain or floodway. Analysis of movable bed streams generally includes a study of the sources of sediment, changes in those sources, and the impact of sediment transport through the floodplain. While NFIP regulations do not specifically address movable bed streams, communities that develop mapping and regulatory standards that address these hazards may receive flood insurancepremium credits through the Community Rating System. The designer should determine if a local community has mapped or enacted an ordinance covering this special hazard. Engineering Principles EndPractices of Retrofitting Flood-Prone Residential Structures IV -47 January 1995 Chapter IV: Determination of Hazards ANALYSIS OF NON-FLOOD-RELATED HAZARDS Non-Flood-Related Hazards Wind Forces Seismic Forces Land Subsidence Figure IV-24: Non-Flood-Related Natural Hazards The designer must be aware that retrofitting actions may trigger a threat from multiple natural hazards and be prepared to address these issues. While floods continue to be a major hazard to homes nationwide, they are not the only natural hazard that causes damage to residential buildings. Parts of the United States are subject to high winds that can accompany thunderstorns, hurricanes, tornadoes, and frontal passages. In addition, many regions are threatened by earthquake fault areas, land subsidence, and fire and snow hazards (Figure IV-24). Retrofitting measures can be designed to modify structures to reduce the chance of damage from wind and other non- flood-related hazards. Fortunately, strengthening a home to resist earthquake damage can also increase its ability to withstand wind damage and flood-related impact and velocity forces. WIND FORCES High winds impose significant forces on a home and the structural elements of its foundation. Damage potential is increased when the wind forces occur in combination with flood forces, as often occurs in coastal areas. In addition, as a structure is elevated to minimize the effects of flood forces, the wind loads on the elevated structure may be increased, depending on the amount of elevation and the structure's exposure to wind forces. Wind forces exert pressure on structural components such as walls, roofs, connections, and foundations. Therefore, wind loads should be considered in the design process at the same time as hydrostatic, hydrodynamic, impact, and building dead and live loads, and loads from other natural hazards such as earthquakes. IV -48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Non-Flood-Related Hazards Wind Design Process Determine base wind speed I Translate wind speed pressures using building code I Apply pressures to entire structure Transfer the lateral sum of these I lateral pressures into the primary resisting frame or shearwalls [Determine wind design pressures for primary resisting frame Check foundation for increased loading due to overturning from lateral loads Design secondary framing members Figure IV-25: Wind Design Process The concept of wind producing significant forces on a structure is based on the velocity difference of a medium (air) striking an obstruction (the structure). Wind speeds vary depending on the location within the United States and the frequency with which these loads occur. Model building codes have adopted isolines showing the wind velocity for an exceedence frequency of 50 years as recommended by the American Society of Civil Engineers (ASCE). The design velocity for a particular site can be determined from these isoline charts. If no local code is in force, the designer should refer to the ASCE 7 Standard, Minimum Design Loads for Buildings and Other Structures. Whatever the governing code or wind load standard in force, the application of the wind loads is primarily the same, and is shown in Figure IV-25 and illustrated in Figure IV-26. Wind Buildingcode Sum of pressures interpretation transferred to and (secondary by shear framing resisted members wallsor primary designed for this uniform resisting frame loading) CLL E 0 Effecton foundation due to momentcreated by overtuming Figure IV-26: Wind Design Process Illustration FEMA recently completed two building performance assessments following Hurricanes Andrew (August 24, 1992) and Iniki (September 11, 1992). FEMA assessed the structural performance of residential building systems damaged by hurricane winds; provided findings and recommendations for enhancing building performance under hurricane wind conditions; and addressed building materials, code compliance, plan review, construction techniques, quality of construction, and construction inspection issues. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -49 January 1995 Chapter IV: Determination of Hazards Copies of these documents can be obtained from FEMA: FEMA (FIA-22), Building Performance: Hurricane Andrew in Florida; Observa- tions, Recommendations and Technical Guidance, February 1993. FEM4 (FIA-23), Building Performance: Hurricane Iniki in Hawaii; Observations, Recommendations and Technical Guidance, March 1993. If no local code is in force, the designer should refer to the ASCE 7 Standard, Minimum DesignLoadsfor Buildings and Other Structures. These reports present detailed engineering discussions of building failure modes along with successful building performance guidance supplemented with design sketches. Please refer to these documents for specific engineering recommendations. SEISMIC FORCES Seismic forces on a home and the structural elements of a foundation can be significant. Seismic forces may also trigger additional hazards such as landslides and soil liquefaction, which can increase the damage potential on a home. Seismic forces act on structural components such as walls, roofs, connections, and foundations. Similar to wind forces, seismic forces should be considered in the design process at the same time as hydrostatic, hydrodynamic, impact, and building dead and live loads, and loads from other natural hazards such as hurricanes. Design assumptions for seismic loadings are normally based upon local building codes. Figures IV-27 and IV-28 illustrate the process for estimating seismic hazards and determining the ability of existing structural components to withstand these forces. IV -50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Non-Flood-Related Hazards Seismic Design Process Determine seismic region Determine lateral loads using building code I Apply loads to the structure in accordance with building code Transfer the lateral load into the primary resisting frame or shear walls Check foundations for increased loading due to overturning from lateral loads Check for lateral forces on elements of structural and non-structural components Design secondary framing members Figure IV-27: Seismic Design Process Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -51 January 1995 Chapter IV: Determination of Hazards Groundmovement Design assumptions based on building code. Lateral forces transferred to and I- Effect on 0 due to earthquake resisted by designed foundation due to wallsor primary moment created resisting frame by overturning Figure IV-28: Seismic Design Process Illustration Additional information concerning the determination of flood- related forces will be available in the next revision of the Flood DesignLoad Criteria incorpo- rated in Section 5 of ASCE 7 Standard, MinimumDesign Loadsfor Buildings and Other Structures, expected to be publishedin 1995. When making repairs to a flood-damaged home or considering retrofitting structures to minimize the impact of future flooding events, there are certain practical steps that can be taken at the same time to reduce the chance of damage from other hazards. Earthquake protection steps can be divided into two categories: steps that deal with the building struc- ture itself, and steps that can be taken with other parts of the building and its contents. Protection of the Structure For the building structure, the most important step is making sure the home is properly bolted onto its foundation so that it will not slide off in an earthquake. Another important step, if raising the foundation to place the house above flood levels, is to make sure the foundation can withstand an earthquake. Key portions of masonry block foundations usually require strengthening by installing reinforcing bars in the blocks and then filling them with concrete grout. FEMA has developed a sample plan for strengthening a masonry block foundation wall. This type of work can be complicated and normally requires the expertise of a professional engineer, architect, or contractor. IV -52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Non-Flood-Related Hazards FEMA's Technical Information on Elevating Substantially Damaged Residential Buildings in the Midwest (August 24, 1993)provides procedures for determining seismic forces and recommendations for seismic retrofitting of a wood- frame structure. For more information on protecting a structure from seismic hazards, contact the appropriate FEMA Regional Office's MitigationDivision. Protection of Non-Structural Building Components and Building Contents The additional cost for seismic strengthening was estimated by For non-structural building components and contents, FEMA (during the Midwest earthquake protection usually involves simpler activities that Flood of 1993) to range from homeowners can undertake themselves. These include 17-23% of the base repair cost anchoring and bracing of fixtures, appliances,chimneys, for elevating a 1,000-SF wood- tanks, cabinets, and shelves. frame structure on masonry foundation walls. FEMA has prepared some simple one-page LAND SUBSIDENCE descriptions (details) and costs associated with these steps that are available in a publication Subsidence of the land surface affects flooding and flood entitled Protecting Your Home from EarthquakeDamage damages. It occurs in at least 38 states. Although there are (1993). no national figures for increased flood damage due to subsidence, it can increase flood damage to entire communities that are subject to coastal flooding, and it threatens larger or smaller areas elsewhere. Because the causes of subsidencevary, selected mitigation techniques are required in different situations. More information on land Subsidence may result in sudden, catastrophic collapses of subsidence hazards can be the land surface or in a slow lowering of the land surface. In obtained from the CRS Commen tarySupplementfor Special either case, it can cause increased hazards to structures and Hazards Credit, dated August infrastructure. In some cases, the causes of subsidence can 1992. This document is available be controlled. through Flood Publications, NFIP/CRS, P.O. Box 501016, Indianapolis, Indiana 46250-Subsidenceis typically a function of withdrawal of fluids or 1016. Telephone (317) 845-gases, the existence of organic soils, or other geotechnical 2898. factors; it requires an extensive engineering/geotechnical Fnnineerinn Prinrinlas and Practices c)f Retrofittinc Flood-Prone Residential Structures IV -53 January 1995 Chapter IV: Determination of Hazards analysis. While NFIP regulations do not specifically address land subsidence, communities that develop mapping and regulatory standards addressing these hazards may receive flood insurance premium credits through the NFIP Community Rating System. The designer should determine if a local community has mapped or enacted an ordinance covering this special hazard. IV -54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations GEOTECHNICAL CONSIDERATIONS Soil properties during conditions of flooding are important factors in the design of any surface intended to resist flood loads. These properties include: Information on land subsidence, * saturated soil pressures (covered previously in Chapter which is sometimes caused by IV under Hydrostatic Forces); flooding conditions, can be found in the Analysis of Non-Flood- Related Hazards Section of * allowablebearing capacity; Chapter IV. * potential for scour; * frost zone location; * permeability;and * shrink-swellpotential. The computation of lateral soil forces and determination of soil bearing capacity are critical in the design of foundations. These forces plus the frost zone location and potential scour play an important role in determining the type of foundation to use. Likewise, the permeability and compactibility of soils are key factors in selecting borrow materials for backfill or levee construction. If unsure of local soil conditions, obtain a copy of the U. S. Department of Agriculture, Natural Resource Conservation Service Soil Survey of the general area. This survey provides valuable information needed to conduct a preliminary evalua tion of the soil properties, including: * type, location, and description of soil types; * use and management of the soil types; and r nninQ II OrinnP inrninoonAn,Prortices of RatrnfiftinnFlnnd-ProneResidentialStructures IV -55 U-111JIanuIary kl I III -_ . ---.9 .5 January 1995 Chapter IV: Determination of Hazards The physical properties of soil are critical to the design, suitability,and overall stability offloodproofingmeasures. Therefore,thedesignershould consult a geotechnical engineer if the soil properties at a site do notsupport the useof the chosen retrofittingmethod.A geotechnicalengineer should also be consulted for any information that cannot be obtainedfromtheSoilSurveyor the local office of the Natural ResourcesConservationService. * engineeringand physical properties including plasticity indexes,permeability,shrink/swellpotential, erosion factors, potential for frost action, and other information. This information canbe compiled using Figure IV-29 (Geotechnical Considerations Decision Matrix) to enable the designer to determine the suitability of the specific soil type to support the various retrofitting methods. It is important to note that while the soil properties may not be optimum for specific retrofitting methods, facilities can often be designed to overcome soil deficiencies. The following sections begin a discussion of the various soil properties, providing the information necessary to fill out the decision matrix (Figure IV-29) and to understand the relationship between these soil properties and retrofitting measures. IV -56 Enaineerina Prinninlas and Practinsa nf Rstrofittinn FRnnd-Prnne Resirdential gtriirtiimr _---------1, r-~---a-- -*w N---.. . . -. .Jna 1995 January 1995 GeotechnicalConsiderations Geotechnical Considerations Decision Matrix - Owner Name: Prepared By: Address: Date: Property Location: \Retrof itting Measures Elevation Flood- on on Fill on Piers on Posts on Piles proofing proofing and Foundation and I Levees Walls Columns TElevation EleatonElvaionElvaio | Relocation Dr We lo Fodals Soil ProDeries i High = Lateral Soil Moderate Pressure High Bearing Moderate Capacity Low High__ _ _ __ Potential for Moderate Scour Low = H igh__ _ _ __ _ _ _ __ _ Moderate_ Shrink/Swell Potential Low H ig h_ _ _ _ _ _ _ _ __ Potential Moderate Front Action Low_ _ H igh _ _ _ _ _ _ __ Moderate_____ Permeability ILow Instructions: This matrix is designed to help the designer identify situations where soil conditions are unsuitable when applied to certain retrofitting measures, therefore eliminating Infeasible measures. It is not intended to select the most suitable alternative. Instructions for use of this matrix follow: 1. Circle the appropriate description for each of the soil properties. 2. Use the NRCS survey, information from this and other reference books, and engineering judgment to determine which methods are Suitable (S)/Not Suitable (NS) for each soil property. Enter S or NS in each box. 3. Review the completed matrix and eliminate any retrofitting measures that are clearly unsuitable for the existing soil conditions. Figure IV-29: Geotechnical Considerations Decision Matrix . _ _ Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -57 Januarv 1995 Chapter IV: Determination of Hazards BEARING CAPACITY et *t-Anothert, important consideration is the allowable bearing An approach developed by capacity of the soil. The weight of the structure, along with FEMA during the elevation of the weight of backfilled soil (if present), creates a vertical substantially damaged homes in Florida and the Midwest is to pressure under the footing that must be resisted by the soil. reuse the existing footings, if The term "allowable bearing pressure" refers to the maxi- allowed by code. mum unit load that can be placed on a soil deposit without causing excessive deformation, shear failure, or consolidation of the underlying soil. The allowable bearing capacity is the ultimate bearing capacity divided by an appropriate factor of safety, typically 2 to 3. QBC = QJFS = lbs/SF where: QBC is the allowable bearing capacity (in pounds per square foot); Q. is the ultimate bearing capacity (in pounds per square foot); FS is a factor of safety, typically 2 or 3 (as prescribed by code.) Formula IV-23: Allowable Bering Capacity Table IV-6 presents estimated bearing capacities for various soil types to be used for preliminary sizing of footings only. The actual allowable soil bearing capacity should be deter mined by a soils engineer. Most local building codes specify an allowable bearing capacity to be utilized in design if the soil properties have not been specifically determined. Once the allowable bearing capacity is determined by the soils engineer or a conservative estimate prescribed by code is made, the designer can determine the capacity of the existing foundation to support the expected loads. Depending on the outcome of that evaluation, the designer may need to supplement the existing footing to support the expected loading condition (i.e., keep the actual bearing IV -58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations Table IV-6 Typical Bearing Pressure by Soil Type (from Table IV-3) SoilType(Symol) Bearing Capacity Soil Type (Symbol) (lb.If.) Clay, Soft (CL, CH) 600 to 1,200 Clay, Firm (CL,CH) 1,500to 2,500 Clay,Stiff (CL, CH) 3,000to 4,500 Loose Sand, Wet (SP, 800 to 1,600 SW, SM) FirmSand, Wet (SP, 1,600to 3,500 SW, sm.SM,SC) 2,700to3,00 Gravel(GW, GP, GM, 2,700 to 3,000 IGC) I _ _ _ __ _ _ Certain types of soil-loose sands and soft clays (SP, SW, SM, SC, CL, CH)-exhibit very poor bearing capacities when saturated; therefore, foundation, levee, and floodwall applications in those conditions would not be feasible without special treatment. pressure below the allowable bearing pressure of the soil) as a result of the retrofitting project. The ability of soils to bear loads, usually expressed as shearing resistance, is a function of many complex factors, including some that are site-specific. A very significant factor affecting shearing resistance is the presence and movement of water within the soil. Under conditions of submergence, some shearing resistance may decrease due to the buoyancy effect of the interstitial water or, in the case of cohesive soils, to physical or chemical changes brought about in clay minerals. While there are many possible site-specific effects of saturation on soil types, some classes of soil can be identified that have generally low shearingresistances under most condi tions of saturation. These include: * fine silty sands of low density, which in some localities may suddenly compact when loaded or shaken, resulting in a phenomenon known as liquefaction; * sand or fine gravel, in which the hydraulic pressure of upward-moving water within the soil equals the weight of the soil, causing the soil to lose its shear strength and become "quicksand," which will not support loads at the surface; and * soils below the water table, which have lower bearing capacity than the same soils above the water table. Other types of saturated soils may also have low shearing resistances under loads, depending on numerous site-specific factors such as slope, hydraulic head, gradient stratigraphic relationships, internal structures, and density. Generally, the soils noted above should not be considered suitable for structural support or backfill for retrofitting, and when they Iv Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ; ~IV-59 January 1995 Chapter IV: Determination of Hazards are known to be present, a soils engineer should be con sulted for site-specific solutions. Mechanicalproperties of all soils are complex. Attempts to construct water- or saturated soil-retaining/resisting structures without a thorough understanding of soil mechanics and analysis of on-site soils can result in expensive mistakes and project failure. SCOUR POTENTIAL Erosion of fill embankments, levees, or berms depends on the velocity, flow direction, and duration of exposure. Scour is localized erosion caused by the entrainment of soil or sediment around flow obstructions, often resulting from flow acceleration and changing flow patterns due to flow constriction. Where flow impinging on a structure is affected by diversion and constriction due to nearby structures or other obstructions, flow conditions estimated for the calculation of depths of scour should be evaluated by a qualified engineer. Scour under building foundations and around supporting walls and posts and the erosion of elevating fill can render structural retrofitting and resistive designs ineffective, possibly resulting in failure. Figures IV-30 and IV-31 illustrate scour at open foundation systems and ground level buildings. Maximum potential scour is critical in designing an el evated foundation system to ensure that failure during and after flooding does not occur due to any loss in bearing capacity or anchoring resistance around the posts, piles, or piers. IV -60 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations a Figure IV-30: Local Scour at Piers, Piles and Posts Depth of Flooding =d Drection of Flow Aa of Greatest Scour Depth at Both Upstream Corners Figure IV-3 1: Scour Action on a Ground-Level Building Engineering Principles and Practices of Retrofitting Flood-Prone ResidentialStructures IV -61 January 1995 Chapter IV: Determination of Hazards J*1 Resistance to scouring increases with clay content and/or the introductionofbondingagents, whichhelpbondthe internal particlesof a soil together. 1*' DScour The factor "a" in Formula IV24 is the diameter of an open foundation member or half of the width of the solid foundation perpendicular to flood flow. The potential for foundation scour is a complex problem. Granular and other consolidated soils in which the individual particles are not cemented to one another are subject to scour erosion and transport by the force of moving water. The greater the velocity or turbulence of the moving water, the greater the scour potential. Soils that contain sufficient proportions of clay to be described as compact are more resistant to scour than the same grain sizes without clay as an intergranular bond. Likewise, soils with angular particle shapes tend to lock in place and resist scour forces. Shallow foundations in areas subject to flood velocity flow may be subject to scour, and appropriate safeguards should be undertaken. These safeguards may include the use of different, more erosion-resistant soils, deeper foundations, surface armoring of the foundation and adjacent areas, and the use of piles. The calculation for estimating maximum potential scour depth at an elevated or ground-level foundation member (Formula IV-24) is based upon the foundation (or foundation member) shape and width, as well as the water velocity and depth, and type of soil. Where elevation on fill is the primary retrofitting measure, embankments must be protected against scour and erosion. at the embankment toe may be calculated as shown in Formula IV-24. IV -62 Enqineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations Estimate Maximum Allowable Scour Investigate presence of underlying strata which would terminate scour action Estimate anticipated scour depth Estimate required depth of foundation members I Interpret results Figure IV-32: Process for Estimating Potential Scour Depth The scour information presented is the best available; however, there is not a general consensus within the scientific community that these scour formulas are valid. Research continues into this area. 05 ) 33 1 = = d[1.1(a/d)0 4 (V/(gdr)feet Where:siai is the maximum potential depth of scour hole (in feet); d is thedepth of flow upstreamof structure (in feet); a is the diameter of post, pier, or pile or half the frontal length of the blockage (in feet); V is the velocity of flow approaching the structure (in feet per second); and g is the acceleration of gravity (32.2 feet per second.) Formula IV-24: Maximum Potential Scour at Embankment Toe The maximum potential scour depth predicted by the following equation represents a maximum depth that could be achieved if the soil material were of a nature that could be displaced by the water's action. However, in many cases, a stronger underlying strata will terminate the scour at a more shallow elevation. Figure IV-32 illustrates the process of determining the potential scour depth affecting a foundation system. Iv Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures TXIVF -63on January 1995 C Chapter IV: Determination of Hazards Step 1: Compute Maximum Allowable Scour. The scour depth at square and circular pier, post, and pile foundation members and/or a ground-level building can be calculated as follows: macall ~~~~~.65.4 a ~~~~S., ( = (d)(K) [ 2-2-. where: variables are the same as in Formula IV-24. For additional information, refer to the document, "Highways in the River Environment" (U.S. Dept. of Transportation, 1987). K is the scour factor for flow angle of attack. K = 1 for buildings perpendicular to flow; additional values of K are shown in Table IV-7. See Figure IV-33. Formula IV-25: Maximum Potential Scour at Structure The above scour equation applies to average soil conditions (2,000 -3,000 psf bearing capacity). Average soil conditions would include gravels (GW, GP, GM and GC), sands (SW, SP, SM, and SC), and silts and clays (ML, CL, MH, CH). For loose sand and hard clay, the maximum scour values may be increased and decreased, respectively, to reflect their lower and higher bearing capacities. However, the assistance of a soils engineer should always be sought when making this adjustment, computing scour depths, and! or designing foundations subject to scour effects. Figure IV-33: Flow Angle of Attack If a wall or foundation member is oriented at an angle to the direction of flow, a multiplying factor, K, can be applied to the scour depth to account for the resulting increase in scour as presented in the following table. IV -64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations Table IV-7 Scour Factor for Flow Angle of Attack, K Length to Width Ratio of Structural Angle of Member In Flow Attack 4 8 12 16 0 1 1 1 1 15 1.15 2 2.5 -3 30 2 2.5 3.5 4.5 45 2.5 3.5 4.5 5 60 2.5 3.5 4.5 6 Numerous scour equations can be utilized to estimate scour depths. The U.S. Department of Trans-Step 2: Investigate Underlying Soil Strata. Once the portation recommends a factor of maximum potential scour depth has been estab safety of 1.5 for predicting lished, the designer should investigate the underly building scour depth. ing soil strata at the site to determine if the underlying soil is of sufficient strength to terminate scour activities. Information from the NRCS Soil Survey may be used to make this assessment. Figure IV-34 illustrates a scour terminating strata. If an underlying terminating strata does not exist at the site, the maximum potential scour estimate will become the anticipated scour depth. However, if an underlying terminating strata exists, the maximum potential scour depth will be modified to reflect this condition, as shown in Step 3. Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures IV -65 January 1995 Chapter IV: Determination of Hazards Foundation Member Flood Protection Elevation w W Erosion Avoided by d Direction of Flow Terminating Strata I i i.. I--,--,---;-_ .-: :. -i1 -.oiI .. i -i ik ----i -_ 1-i '-.: / Figure IV-34: Tenninating Strata Step 3: Determine the Anticipated Scour Depth. Based on the results of Step 2, the designer will determine the anticipated scour depth to be used in determining the depth to which the foundation element must be placed to resist scour effects. If a terminating strata exists, the expected scour would stop at the depth at' which this strata starts, and the distance from this point to the surface is considered to be the potential scour depth, (Sd),Figure IV-34. If no terminating strata exists, the maximum potential scour (smax) computed earlier becomes the potential scour depth (Sd). IV -66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Geotechnical Considerations Step 4: Determine Required Depth of Foundation Members. Scour will increase the height above grade of the vertical member, since the grade level would be lowered due to scour and erosion (see Figure IV-35). As this occurs, the depth of burial (Db)of the vertical foundation member also decreases an identical distance. This can result in a foundation failure because the loss of supporting soils would change the assumed conditions under which the elevated foundation system was designed. To account for this, the vertical foundation member depth used for the purpose of determining an acceptable design must be increased by the amount of potential scour depth, (Sd). a D, Additional Depth of Sd Embedment Required Figure IV-35: Additional Embedment Step 5: Interpret Results. Foundations, footings, and any supporting members should be protected at least to the anticipated scour depth. If the structural member cannot be buried deeper than the anticipated scour depth, the member should be protected from scour by placing rip-rap (or other erosion-resistant material) around the member, or by diverting flow around the foundation member with grading modification or construction of an independent barrier (floodwall or levee). For Pnninoerinn Prinrinlps and Prartircs of Retrofittino Flood-Prone Residential Structures IV -67 Januay 15_ A , ... .-__r- January 1 995 Chapter IV: Determination of Hazards situations in which the anticipated scour depth is minimal,the designer should use engineering judgment to determine the required protective measures. Whenever the designer is unsure of the appropriate action, a qualified geotechnical engineer should be consulted. FROST ZONE CONSIDERATIONS Because certain soils under specific conditions expand upon freezing, the retrofitting designer must consider the frost heave impactin the design of shallow foundations. When frost-susceptible soils are in contact with moisture and subjected to freezing temperatures, they can imbibe water and undergo very large expansions (both horizontally and At vertically). Such heave or expansion exerts forces strong enough to move and/or crack adjacent structures (founda- Localbuildingcodes generally tions, footings, etc.). The thawing of frozen soil usually specifythe depthof the zone proceeds from the top downward. The melted water cannot of maximum frost penetration. drain into the frozen subsoil, and thus becomes trapped, In the absenceof guidance in possibly weakening the soil. Normally, footing movements the local building code, refer to the NationalWeather caused by frost action can be avoided by placing part of a Serviceorthe NRCS Soil foundation below the zone of maximum frost penetration. Survey. PERMEABILITY Of principal concern for the construction of retrofitting measures such as levees and floodwalls arethe properties of the proposed fill material and/or underlying soils. These properties will have an impact on stability and will deter mine the need for seepage and other drainage control measures. IV -68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 While impervious cutoffs such as compacted impervious core, sheet pile metal curtains, or cementitious grout curtains can be designed to reduce or eliminate seepage, their costs are beyond the financial capabilities of most homeowners. However, several lower-cost measures to control seepage include pervious trenches, pressure relief wells, drainage blankets, and drainage toes. It is very important that the designer keep the units in this formula consistent. The results of Formula IV-26 depend on the homogeneity of the foundation and the accuracy of the coefficient of permeability. The results should be considered as an indication only of the order of magnitude of seepage through a foundation. GeotechnicalConsiderations Since most retrofitting projects are constructed using locally available materials, it is possible that homogenous and impermeable materials will not be available to construct embankments and/or backfill floodwalls and foundations. Therefore, it is essential that the designer determine the physical properties of the underlying and borrowed soils. Where compacted soils are highly permeable (i.e., sandy soils), significant seepage through an embankment and under a floodwall foundation can occur. Various soil types and their permeabilities are provided in Table IV-8. The coefficient of permeability provides an estimate of ability of a specific soil to transmit seepage. It can be used (Formula IV-26) to make a rough approximation of the amount of foundation underseepage. Formula IV-26 may be used in lieu of Formula IV- 17 for large levee/floodwall applications when the coefficient of permeability for the specific site soil is known. Q=ki hg A where: Q is the discharge in a given unit of time; k is the coefficient of permeability for the soil foundation (in feet per unit of time); ihg is the hydraulic gradient (h/L) which is the difference in head between two points divided by the length of path between two points (dimensionless); and A is the gross area of the foundation through which flow takes place (in square feet). Formula IV-26: Volume of Seepage Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -69 January 1995 Chapter IV: Determination of Hazards SHRINK-SWELL POTENTIAL As mentioned earlier in this chapter, due to the continual shrink and swell of expansive soil backfills and the variation of their water content, the stability and elevation of these Soilthat exhibit severe shrink-soils and overlaying soil layers may vary considerably. Soils that exhibit severe shrink- swell characteristics includeclays These characteristics make the use of these soils in engiand clay mixtures such as soil neering/construction applications imprudent. The NRCS types CH, CL, ML-CL, SC, and Soil Survey for a specific area offers guidance on the shrink- MH. swell potential of each soil group in the area as well as guidance on the suitability of their use in a variety of applications including engineering, construction, and water retention activities. If the designer is unsure of the type or nature of soil at the specific site, a qualified soils engineer should be contacted for assistance. The physical soil parameters at the retrofitting and potential borrow sites are an important design consideration. Homeowners and designers should clearly understand that the advice of a professional soils engineer is vital when planning retrofitting measures that are not ideal for the physical soil parameters at a given site. IV -70 Enaineerino PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Geotechnical Considerations TableIV-8 Typical Values of Coefficient of Permeability kfor Soils I Soil Type and Description Well-graded clean gravels, gravel-sand mixtures Poorly graded clean gravels, gravel-sand-silt Silty gravels, poorly graded gravel-sand-silt Clayey gravels, poorly graded gravel-sand-clay Well-graded clean sands, gravelly sands Poorly graded clean sands, sand-gravel mix Silty sands, poorly graded sand-silt mix Sand-silt clay mix with slightly plastic fines Clayey sands, poorly graded sand-clay mix Inorganic silts and clayey silts Mixture of inorganic silt and clay Inorganicclays of low to medium plasticity Organic silts and silt-clays, low plasticity Inorganic clayey silts, elastic silts Inorganic clays of high plasticity Organic clays and silty clays Typical Coefficient of Symbol I Permeability, Ft/Day GW GP GM GC SW SP SM SM-SC SC ML ML-CL CL OL MH CH OH 75 180 1.5 x 10-3 1.5 x 10-4 4.0 4.0 2 x 10.2 3.0x 10-3 7.5 x 10-4 1.5 x 10-3 3.0 x 10-4 1.5 x 10-4 Quite variable 1.5 x 10-4 1.5 x 10-2 Quite variable 1 1. 1 cm/sec= 2,840 ft/day = 2 ft/min 1 ft/year = 1 x 10-6cm/sec Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures IV -71 January 1995 CHAPTERV .. I BENEFIT/COST ANALYSISAND ALTERNATIVE SELECTION Featuring: Evaluate Hazards Estimate Potential Damages (No Action Alternative) Identify CostsAssociatedwith Alternatives Estimate Benefits Compute Benefit/Cost Ratio and Net Present Value Select a Method /001ii II I BENEFIT/COST ANALYSIS AND ALTERNATIVE SELECTION I IF 200 . Chapter V: Benefit/Cost Analysis and Alternative Selection Table of Contents The Benefit/Cost Analysis Process ................................................ V -1 Evaluate Hazards ............................................... V -3 Estimate the Potential Damages (No Action Alternative) .......................................... V -3 Costs Associated with Alternatives ............ Estimate Benefits ................................................ Compute Benefit/Cost Ratio and Net Present Value ................................................ Evaluate Results ............................................... Select a Method ............................................... Evaluate Hazards ............................................... V.3...................................V -4 V -4 V -4 V -5 V -6 Determine Flood Frequency, Discharge, and Elevation .............................................. V -7 Compile DischargeVersus Exceedence Probability Curve .........................................V -7 Estimate Potential Damages ............................................... V -9 Identify Costs Associated with Alternatives ............................................... V -13 Estimate Benefits ........... V-14 Compute Benefit/Cost Ratio and Net Present Value . .. V -19 Convert Estimated Annual Benefits to a Present Value . .. V -20 Convert Estimated Costs of Retrofitting to a Present Value .. V -21 Compute the Benefit/Cost Ratio and/or Net Benefit .. V -22 Select a Method .. V-25 Detailed Cost Estimating ... V -28 Sources for Unit Costs ... V -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -i January 1995 BENEFIT/COST ANALYSIS AND ALTERNATIVE SELECTION Benefit/cost analysis is a powerful tool to help determine whether the benefits of a prospective hazard mitigation project are sufficient to justify the costs ofthe project. This analysis can also be used to assist in ranking different retrofitting alternatives. A user's guide and computer disks for a computer model, Benefit/Cost Analysis of Hazard Mitigation Proj ects, developed by FEMA is included as Appendix E to this manual. The benefits calculated by the model are expected future benefits estimated over the useful lifetime of the retrofit project. To account for the time value of money, a net present value is calculated automatically by the model. THE BENEFIT/COST ANALYSIS PROCESS Benefit/cost analysis provides estimates of the benefits and -I,' costs of aproposedproject. The term "benefit/cost analysis" is used to denote economic analyses that apply either the maximum present value criterion or the benefit/cost ratio criterion to Benefit/Costvs. Cost-Effective evaluate prospective actions. Both costs and benefits are Analysis. Benefit/cost analysis differs from cost-effectiveness discounted to their present values The maximum present value analysis in one major way-it criterion subtracts costs from benefits to determine if benefits considers a project's merits (or exceed costs. Benefit/cost ratios provide an alternative evaluabenefits). Analysis of cost- tion: prospective actions in which benefits exceed costs have effectiveness simply identifies the benefit/cost ratios above 1.0. least expensive way to achieve an objective. Benefit/cost analysis also takes into account the usually different benefits of various I retrofitting measures. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: BenefitlCost Analysis and Alternative Selection __W The "benefits" considered in a retrofitting measure are the future damages and losses that are expected to be avoided as a result of the measure. Evaluate Hazards i Estimate Potential Damages I Identify Costs for Each Alternative I Identify Benefits for Each Alternative i Compute B/C Ratio and Net Present Value for Each Alternative I 4 Evaluate Results . Select a Method The logic of benefit/cost analysis implies that the alternative with the highest maximum present value or highest benefit/cost ratio is the desired alternative. The benefits of retrofitting projects are avoided future damages. Benefits are not the damages incurred in an event already experienced, even if such damages would have been avoided by the retrofit project. Rather, benefits are the present value of the sum of expected avoided future damages for all levels of intensity offuture floods. To estimate future damages (and the benefits of avoiding them), the probabilities of future events must be considered. The probabilities of future events profoundly affect whether or not a proposed retrofitting measure is cost effective. The benefits of avoiding flood damage for a building in the 10-year floodplain will be enormously greater than the benefits of avoiding flood damage for an identical building situated at the 1,000-year flood 0 level. Each proposed retrofitting project must be evaluated on its own merits, comparing the benefits and costs of a specific project and/or alternatives. In particular, the benefits of a project may vary markedly depending on the vulnerability of the existing home to damages and losses, the probabilities of future damages, and the effectiveness of the mitigation measure in avoiding future damages. Figure V-1 presents the basic steps in performing any benefit/ cost analysis. These steps are summarized below. Figure V-I: Benefit/Cost Analysis Process S Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 The Benefit/Cost Analysis Process EVALUATE HAZARDS Conducting a benefit/cost analysis of flood hazard mitigation projects requires estimating the expected frequency and severity of flooding in the area under consideration. Detailed flood information is given in Flood Insurance Studies (FISs) and on Flood Insurance Rate Maps (FIRMs) where such studies are available. In some cases, estimates of expected flood frequency and severity may have to be made. State, local, and privately prepared studies may exist as well. Chapter IV-Determination of Hazards-provides guidance on the development of the flood hazard information required for conducting a benefit/cost analysis. ESTIMATE THE POTENTIAL DAMAGES (NO ACTION ALTERNATIVE) Estimating the benefits of prospective flood hazard mitigation projects requires site-specific data to establish expected damages as a function of flood depth (and other flood hazards such as high velocity, ice/debris flows, or soil failure, where appropriate). The expected flood hazard relationships developed in the previous step are used in conjunction with actuarial flood damage data developed from FIA flood insurance claim data and compiled in tables and graphs of damage versus depth of flooding. The flood hazard mitigation benefit/cost computer model presented in Appendix E considers property damage and certain other economic losses. COSTS ASSOCIATED WITH ALTERNATIVES The costs of a flood hazard mitigation project vary according to the retrofitting measure and generally include direct construction costs, engineering or architectural design fees, permit fees, contractor's fees, the cost of temporary living quarters, and loss of income due to design/construction activities. Guidance on estimating these costs is provided in Chapter III. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: Benefit/Cost Analysisand Alternative Selection INA of.*,%T FEMA has developed a computer program,Benefit/Cost Analysis of Hazard Mitigation Projects (see Appendix E), which can be used to evaluate the benefiticost ratio of the flood hazard mitigation measures presented in this manual. The program requires an IBM- compatible computer with 15 Mb of availablehard disk storage, 4 Mb of available RAM, and a color monitor, and the QuattroTM Pro for Windowsspreadsheet. ESTIMATE BENEFITS The benefits of a flood hazard mitigation project are the avoided future damages. Benefits cannot be determined exactly because the times and severity of future flooding events are not known exactly. Rather, benefits are estimated by probability, based on experienced or hypothetical floods of various severity. COMPUTE BENEFIT/COST RATIO AND NET PRESENT VALUE The computation of benefit/cost values involves discounting projected benefits and their associated costs to their present values and computing either a benefit/cost ratio or a maximum present value. Benefit/cost ratios of 1.0 or greater and positive net present values indicate a cost-beneficial project. EVALUATE RESULTS The results of a benefit/cost analysis include the present value of damages and losses avoided, costs of the specific retrofitting measure, and calculation of either the net present value or benefit/cost ratio. As previously stated, alternatives with a positive net present value or a benefit/cost ratio greater than 1.0 indicate a cost-beneficial project. Where more than one alternative is being considered, the aforementioned results should be tabulated and compared for each alternative. Ranking ofthe alternatives from the highest to lowest net present value or benefit/cost ratio will indicate the desirability (from a benefit/cost standpoint) of each alternative with respect to other alternatives. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 The BenefitlCost Analysis Process For guidance on performing benefit/cost analysis using manual methods, please refer to "How to Evaluate Your Options" prepared by the U.S. Army Corps of Engineers National Flood Proofing Committee. A complete reference for this document is provided in Appendix C. SELECT A METHOD The existence of a favorable benefit/cost ratio is not the sole factor for the selection of a retrofitting measure. Other economic, technical, and subjective factors can influence the homeowner's selection of a retrofitting measure. Conducting a benefit/cost analysis for a flood hazard mitigation project requires various data and judgments to estimate the expected frequencies and intensities of damage-producing flood events. Further estimates are made of both the benefits and costs associated with the different retrofitting measures. The calculations involved with establishing these estimates can be fairly complicated. FEMA's computer program (see Appendix E) addresses many of these complexities. Engineering Principles and Practices of F RetrofittingFlood-Prone Residential Structures January 1995 Chapter V: BenefitlCost Analysis and Alternative Selection EVALUATE HAZARDS Determine Flood Frequency, Discharge and Elevation Compile Discharge vs. Exceedence Probability Curve Figure V-2: Critical Steps in Evaluating Flood Hazards A Flood Insurance Study (FIS) consists of an FIS report, Flood Insurance Rate Map (FIRM), and (in non-coastal floodplains) a Flood Boundary and Floodway Map (FBFM). The FIS report describes how the flood hazard information was developed for the community. The FIRM shows areas inundated during a 100-year flood event. The FBFM delineates the regulatory floodway adopted within the community. To perform a benefit/cost analysis, the flood hazard to the structure in question must be determined in terms of the frequency and intensity of expected floods. The hazard analysis must include the expected frequency of flood hazards (e.g., a 50-year flood), depth offlooding, and in the case of'riverine flooding, the corresponding intensity or severity of the flood [e.g., discharge of 1,500 cubic feet per second (cfs)]. To perform an economic analysis inriverine flooding situations, the relationship between discharge and water-surface elevation (often referred to as the rating curve, depicted in Figure V-3) and the relationship between discharge and exceedence probability must be known. This section describes how to develop this data (the process is illustrated in Figure V-2). In coastal A Zones, FISs provide a table of the flood frequency versus flood elevation relationship. 129 126 127 0 126 z t 125 z 0 F 124 4 LU W 123 0 0 -J 122 LL 121 120 119 L 0 400 800 1,200 1,600 2,000 2,401 DISCHARGE (CFS) Figure V-3: Discharge Versus Elevation (Rating Curve) v-6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1 995 To obtain a copy of the FIS for the community in question, contact FEMA at 1-800-358-9616. The various agencies that maintain flood informationare listed in Appendix C. Evaluate Hazards DETERMINE FLOOD FREQUENCY, DISCHARGE, AND ELEVATION Several tools exist that can be utilized to obtain information on the flood hazards affecting the structure in question. A Flood Insurance Study (FIS) is available for most flood-prone communities throughout the United States. In some cases, an FIS may not be available for a community, or it may have insufficient data for the flooding source affecting the building. In these cases, the designer can turn to the U.S. Army Corps of Engineers (USACE) and Natural Resources Conservation Service (NRCS), which provide flood hazard information reports for many flooding sources. The U.S. Geological Survey (USGS) and the Tennessee Valley Authority (TVA) also publish stream gaging data and have flood information reports for various flooding sources. State or local floodplain studies may also be available for the community. For more infonnation concerning available data, contact the floodplain management services office of the USACE or the local offices ofthe USGS, TVA, NRCS, or your municipal engineer, floodplain administrator, flood control district, or water control boards. COMPILE DISCHARGE VERSUS EXCEEDENCE PROBABILITY CURVE For riverine A Zone scenarios, FEMA' s benefit/cost computer program takes the data for flood frequency, discharge, and elevation and automatically compiles the discharge versus elevation and discharge versus exceedence probability curves. This information is critical for the development of the depth- damage relationships presented in the next step. Coastal A Zone flood models are based on storm surge models or tide gage analyses, which predict flood elevations. The FIS gives flood elevations relative to a benchmark elevation, generally the National Geodetic Vertical Datum of 1929 (NGVD). Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: Benefit/CostAnalysis and Alternative Selection Unlike riverine FIS data, flood data given in the FIS for coastal A Zones includes a table of exceedence probability (flood frequency) versus flood elevation. FEMA's benefit/cost computer model analyzes these data and creates a smooth curve relating exceedence probability and flood depth. This regression fit gives the annual exceedence probability for all floods in one-foot increments of depth. From the annual exceedence probabilities, calculated as de scribed above, the expected annual number of floods in a given one-foot increment is calculated by difference. For example, the expected annual number ofa two-foot flood (i.e., all floods between 1.5 and 2.5 feet) is calculated as the exceedence probability for a 1.5-foot flood minus the exceedence probabil- Determine Flood ity for a 2.5-foot flood. Frequency, Discharge and Elevation For a given coastal area covered by an FIS and a FIRM, the elevations of the 10-, 50-, 100-, and 500-year floods are Compile Discharge vs. Exceedence constantover the entire area. However, the probability of a Probability Curve given flood depth occurring at a specific site depends very _MMMNMMMMMM strongly on the elevation of the particular site. Thus, the Zero Figure V-4: Critical Steps in Evaluating Flood Flood Depth Elevation ofthe facility under evaluation has a Hazards profound impact on the degree of flood risk experienced at the site. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Estimate Potential Damages ESTIMATE POTENTIAL DAMAGES Estimating the potential damages to a structure for the no-action (before mitigation) alternative is a critical step in the overall development of expected benefits from retrofitting measures. The potential damages (flooding depth and loss of function) from the no-action alternative serve as the baseline from which future avoided damages can be computed for various retrofitting alternatives. Data regarding depth-damage relationships from FIA data tables (Figure V-5), which express damage to a building as a percentage ofthe building replacement value, or the analyst's data can be input to FEMA's benefit/cost analysis computer program, which will then prepare flood depth-versus-damage and probability-versus-damage relationships. The estimated damages and losses for the existing building at each flood depth depend on the depth-damage functions for items such as building and contents, displacement, and rental losses. The expected damages and losses also depend very strongly onthe degree of flood risk at the site under evaluation. Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures V -9 January 1995 Chapter V: BenefitlCost Analysis and Alternative Selection Flood Insurance Administration (FIA) Depth-Building Damage Data Building Damage Percent by Building Type (based upon replacement value) 1 Story 2 Story Split Level 1 or 2 Split Level Flood without without without Story with with Mobile Depth Basement Basement Basement Basement Basement Home -2 0 0 0 4 3 0 -1 0 0 0 8 5 0 0 9 5 3 11 6 8 1 14 9 9 15 16 44 2 22 13 13 20 19 63 3 27 18 25 23 22 73 4 29 20 27 28 27 78 5 30 22 28 33 32 80 6 40 24 33 38 35 81 7 43 26 34 44 36 82 8 44 29 41 49 44 82 9 45 33 43 51 48 82 10 46 38 45 53 50 82 11 47 38 46 55 52 82 12 48 38 47 57 54 82 13 49 38 47 59 56 82 14 50 38 47 60 58 82 1 5 50 38 47 60 58 82 16 50 38 47 60 58 82 17 50 38 47 60 58 82 18 50 38 47 60 58 82 Figure V-5: FIA Depth-Damage Data Table Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Estimate Potential Damages Scenario damages are based on depth of flooding, not on flood hazard risk. Two identical buildings at different locations will have identical scenario damages, given the same depth of flooding. __v.' Even for buildings with high expected annual damages, mitigation projects are not necessarily cost-beneficial. Whether or not a project is cost-beneficial depends on the cost of the mitigation project and on the effectiveness of the mitigation project in avoiding damages, as well as on the expected annual damages. FEMA's benefitlcost ratio model characterizes losses expected both before and after mitigation as follows: Scenario Damages: Scenario damages indicate the estimated damages that would result from a single flood of a particular depth at the building under evaluation. For example, the scenario damages for a three-foot flood are the expected damages and losseseach time a three-foot flood occurs at a particular site. Scenariodamagesdo NOT depend on the probabilityof floods at that location. The model tabulates scenario damages for each flood depth from -2 to 18 feet for building damages, contents damages, displacement costs, and rental income losses (as well as other categories not applicable to residences). The total damages and losses are shown for each flood depth. This information shows the total vulnerability ofthe existing building to flood damage, how these damages are distributed among different categories of damages, and how these damages vary with flood depth. Expected Annual Damages: Expected annual damages take into account the annual probabilities of floods of each depth. Expected annual damages are the average damages per year expected over a long time period. "Expected annual" does not mean that these damages will occur every year. For each flood depth, expected annual damages are calculated by multiplying the scenario damages times the expected annual number (probability) of floods of each depth. The expected annual damages are tabulated in the same way as scenario damages. Expected annual damages will generally be much smaller than scenario damages because the expected annual number or annual probability of a flood of a given depth is usually much less than one. Enaineering Principles and Practices of I RetrofittingFlood-Prone Residential Structures January 1995 Chapter V: Scenario damages and expected annual damages provide different information. Scenario damages describe how bad flood damages will be each time a flood occurs. How- ever, because scenario damages do not consider flood probabilities, theydo not providesufficient information for decision making. Scenariodamages for a given flood depth may be high, but if the flood probability is very low, no mitigation actionmay be warranted.If a five- foot flood causes$50,000in dam- ages but such a flood is expected to occur only once in 1,000 years, then simply repairing the very infrequent flood damage may be the most sensiblestrategy. Benefit/Cost Analysis and Alternative Selection The scenario damages before mitigation and the expected annual damages before mitigation provide, in combination, a complete picture ofthe vulnerability ofthe building to flood damage before undertaking a mitigation project. Expected annual damages consider flood probabilities. A building with high expected annual damages means that not only are scenario damages high, but also that flood probabilities are relatvely high. If expected annual damages arehigh, thenthere will be high potential benefits in avoiding such damages. Damages after mitigation depend on the damage before mitigation and damage befoe on the mitigat tionandonthe effectiveness ofthemitigationmeasurein avoiding damages. The expected annual damages and losses after mitigation also depend very strongly on the degree of flood risk at the site under evaluation. For some mitigation projects, such as relocation or buyout, the scenario damages and ex ected annual losses after mitigation will be zero. For other p mitigation projects, such as elevation or flood barriers, scenario damages and expected annual losses after mitigation will be lower than before mitigation but not zero. FEMA's benefitlcost ratio model tabulates after-mitigation losses in the same way as before-mitigation losses. V-12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Estimate Benefits IDENTIFY COSTS ASSOCIATED WITH ALTERNATIVES Once a detailed review ofthe flood hazard and associated losses has been performed, the costs associated with each of the technically feasible alternative retrofitting measures must be determined. Developing detailed construction cost estimates is crucial to ensuring that the homeowner can afford to complete the project. In Chapter III, a methodology for developing preliminary estimates of the cost of various retrofitting measures was presented. The methodology for developing detailed construction costs is similar, but requires more detail and definition ofproject component quantities and unit costs and often occurs after the preliminary economic analysis. Gener ally, the designer's/homeowner's approach to examining retrofit alternatives and selecting the one that is most appropri ate is an iterative cycle including these steps: e examine technical feasibility of alternatives; * develop preliminary cost estimates of each alternative being considered; * model benefit/cost ratios of considered alternatives; * rank alternatives based on benefit/cost ratios; * develop more detailed design study(ies) of highly ranked alternative(s) and detailed cost estimate(s); and * refine benefit/cost model(s) if previous step yields cost figure(s) significantly different from previous estimate(s), and re-rank alternatives as indicated based on new ratios and homeowner preference. Detailed cost estimating is discussed later in this chapter. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -13 January 1995 Chapter V: Benefit(CostAnalysis and Alternative Selection ESTIMATE BENEFITS Expected Annual Damages I ONOWNEOMMME Expected Annual Avoided Damages I Figure V-6: Types of Benefits Evaluated The benefits of a flood hazard mitigation project are the reduction in damages that would otherwise be expected. Expected annual benefits are defined as the sum of expected avoided damages. The computer program presented in Appendix E automatically computes values for the types of damages illustrated in Figure V-6 and explained below. Scenario Damages: The expecteddamages per flood event of a given flood depth at the residence. Scenario damages (SCD) are the sum of building damages (BD), contents damages (CD), displacement costs (DIS), and rental income losses (RENT) for floods of each depth per scenario. FornulaV-i: Scenario Damages Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January1995 Estimate Benefits * Building Damages: (BD) are defined as the product of floor area ofthe building (FA), replacement value of the building per square foot (BRV), and the modified/depth damage function (MDDF), which is the expected damage by flood depth expressed as a percentage of building replacement value. -. 13 BD = (FA) (BRV) (MDDF) M where: BD is the total amount of building damage per scenario in dollars; FA is the floor area ofthe building (in square feet); BRV isthe replacement value of the building (dollars per square foot); and MDDF is the expected damage by flood depth,expressed as a percentage of building value. Formula V-2: Building Damages * Contents Damages: (CD) are estimated as the product of the expected contents damage (ECD) and the total building contents replacement value (CRV) for each flood depth. Building and contents damages can also be taken from the depth-damage curves developed by FIA. I OI CD = (ECD) (CRV) *Im where: CD is the total contents damage in dollars; ECD is the expected contents damage by flood depth,expressed as a percentage of contents replacement value; and CRV is the total building contents replacement value in dollars. FormulaV-3: Contents Damages Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V-15 January 1995 Chapter V: BenefitiCostAnalysis and Alternative Selection * Displacement Costs: (DIS) are defined as the product of displacement days necessary (DD), the total costs of displacement per day per SF (TDC), and the total area occupied (TA). DIS = (DD) (TDC) (TA) where: DIS is therelocation cost in dollars; DD is the estimated number of displacement days necessary for floods of flood depth; TDC is the estimated displacement costs per day per SF; and TA is the total area occupied in SF. Formula V-4: Displacement Costs * Rental Income: Losses are also included if all or part of the residence is rented. Rental income losses (RENT) are the product of displacement days (DD) and the daily rental rate (DRR). Formula V-5: Rental Income Losses Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Januarv 1995 Estimate Benefits * Expected Annual Damages: Expected annual damages (AD) are the product of scenario damages (SCD) and the expected annual number of floods of a given depth EAE): AD = (SCD) (EAE) where: AD is the expected annual damages in dollars; SCD is the scenario damages (as defined previously) in dollars; and EAE is the expected annual number of floods of a given depth. Fornula V-6: Expected Annual Damages * Expected Avoided Damages: Expected avoided damages (AVD) are the product of scenario damages (SCD), the expected annual number of floods (EAE), and the effectiveness ofthe mitigation measure (EFF): I. AVD= (SCD) (EAE) (EFF) where: AVD is the expected avoided damages in dollars; SCD are scenario damages for each damaging flood of a given depth (in dollars); EAE is the expected annual number of floods of a given depth; and EFF is the effectiveness ofthe mitigation measure in reducing expected damages from a flood of a given depth (percent of expected damages expressed as a decimal equivalent). Formula V-7: Expected Avoided Damages Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: BenefitlCost Analysis and Alternative Selection a Expected Annual Benefits: The expected annual benefits (AB) ofa hazard mitigation project are the sum of expected avoided damages (AVD) over the range of flood depths considered. FEMA's benefit/cost model (see Appendix E) includes a range of from -2 feet to 18 feet. .lol L @R'a AB= max X AVD RF=min where: AB is the expected annual benefits in dollars; RF is the flood depth considered above the zero flood depth elevation (in feet); mi isthe minimum damaging flood considered above the zero flood depth elevation (in feet); max is the maximum flood depth considered above the zero flood depth elevation (in feet); and AVD is the expected annual avoided damages frorn each flood depth above the zero flood depth elevation considered (in dollars). Formula V-8: Expected Annual Benefits Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Compute Benefit/Cost Ratio and Net Present Value COMPUTE BENEFIT/COST RATIO AND NET PRESENT VALUE One important aspect of benefit/cost analysis is accounting for the time value of money. The value of money changes over time due to economic, political, and other factors. Interest rate changes may impact the estimation of costs and benefits expected to occur in the future. For that reason, benefit/cost analysis requires a common basis for comparing estimates ofproject costs and benefits. This is usually accomplished by converting present, future, and annual project costs and benefitsto a common basis suchas present value, future value, or average annual values. The assumed interest rate, or discount rate, is the factor that controls the conversion of future values to present values. Increasing the discount rate lowers the present value of future benefits/costs and, conversely, lowering the discount rate raises the present value of future benefits/costs. As previously mentioned, either the benefit/cost ratio or maxi- Formulashereareautomatedin mum present value (net benefit) criterion can be used to evalu- FEMA'sbenefitlcostprogram ate each prospective retrofitting action. Earlier sections of this (AppendixE). chapter have built the foundation for completion of the analyses _______________________ discussedbelow. 0nninrin Drinpinle canr4 Prar-tig-a of RatrnfiffinnFloord-ProneRAsidentialStructures V -19 JlllCVl1Wau I995--. . ary1 vg January 1995 ChapterV: Convert Estimated Benefits to Present Value Convert Estimated Costs to Present Value Compute BenefitfCost Ratio Figure V-7: Critical Steps in Benefit/Cost Ratio Analysis Benefit/Cost Analysis and Alternative Selection CONVERT ESTIMATED ANNUAL BENEFITS TO A PRESENT VALUE After determining the average annual damage to be prevented by the retrofitting measure, the present worth of damages prevented over the expected life of the structure can be determined. To make this determination, one must first assume the building's life expectancy; this will normally be the useful life of the structure. However, analysts can use the period the homeowner plans to occupy the home, or the length of the mortgage. Secondly, an interest rate for borrowing money to retrofit must be assumed. This rate may be obtained from any bank. The analyst can then use the following formula to computea present worth factor for the assumed life of the structure and the assumed interest rate: (1 + i)n where: PWI is the present worth factor; n is the assumed life of the structure (years); and i is the assumed interest rate for borrowing money (decimal equivalent of percent per year). Formula V-9: Present Worth Factor S Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures January 1995 Compute Benefit/Cost Ratio and Net Present Value Multiply the average annual damage prevented by retrofitting by the present worth factor to determine the present-day value of these expected flood damages avoided. *fi EABpV = (PWF) (AB) where: EABpvis the present value of estimated annual benefits in dollars; PWF is the present worth factor; and AB is the expected annual benefits of a mitigation project in dollars. FormulaV-10: PresentValue of Estimated Annual Benefits CONVERT ESTIMATEDCOSTS OF RETROFITTING TO A PRESENT VALUE The primary cost of a retrofitting measure will be the engineering and construction costs, which already represent present-day values. Should the retrofitting measure require annual operation and maintenance costs (including replacements), these estimated periodic costs should be converted to a present-day value, using the same methodology previously employed to convert annual benefits to a present value worth. EACPV= (PWF) (AC) + ECCPV where: EACpvis the present value of estimated annual costs in dollars; PWF is the present worthfactor; AC is the expected annual cost (in dollars) for operation and maintenance of a specific retrofitting measure; and ECCpvis the present value of the engineering and construction costs associated with a specific retrofitting measure, in dollars. Formula V- I 1: Present Valueof Estimated Annual Costs Retrofittina Flood-Prone Residential Structures V -21 Ennineerinn Prinrnin~l and Practices of January 1995 Chapter V: Benefit/Cost Analysis and Alternative Selection COMPUTE THE BENEFIT/COST RATIO AND/OR NET BENEFIT Once the present value of the benefits and costs associated with a retrofitting measure is computed, dividing the present value ofthe benefits by the present value ofthe costs will enable the designer to fairly evaluate a number of retrofitting alternatives. BCR = EABPV / EACPV - where: BCR is the benefit/cost ratio; EACPV is the present value of estimated annual costs in dollars; and EABPV is the present value of estimated annual benefit in dollars. Formula V- 12: Benefit/Cost Ratio An alternative evaluation measure is to subtract the present value of the costs from the present value of the benefits. no NPV =EAB -EACPV where: NPV is the net present value or benefit ofthe mitigation measure; EACPV is the present value of estimated annual costs in dollars; and EABPV isthe present value of estimated annual benefits in dollars. Formula V-13: Net Present Value Engineering Principlesand Practicesof Retrofitting Flood-Prone Residential Structures January 1 995 Compute Benefit/Cost Ratio and Net Present Value A benefitlcost ratio of 1.0 or greater indicates that the benefits of the retrofitting alternative exceed the costs. The alternative with the highest benefit/cost ratio or net benefit would be the preferred alternative from an economic perspective, if the same level of protection (design flood) is being evaluated. It should be pointed out that the entire procedure of generating a benefit/cost ratio is not an exact science but instead a subjective process. The creation of a benefit/cost ratio is intended to give an idea of the cost effectiveness of a specific retrofitting technique in comparison to the other options available. As long as the same procedures are utilized in all scenarios, the ratio should provide the designer with an idea ofthe relative cost effectiveness of all options. Benefit/costmodelscanbe usedto optimizethe selectionofa retrofitting measure by analyzing incremental improvements to a selected alternative. This is accomplished by maximizing (avoided damages) benefits while minimizing project costs. It is an iterative process whereby an original retrofitting solution is modified by adding or deleting design features and/or designated protection levels. Each modification will have an impact on the project benefits and costs and subsequently the benefit/ cost ratio. This technique will assess the relationship between increased (decreased) cost and increased (decreased) effectiveness for the range of modifications with a particular retrofitting measure analyzed. The following example illustrates this optimizationtechnique. Pnnineerinm Prinninipe and Practices of IRetrofittinoFlood-Prone Residential Structures V -23 January 1995 8&A ---- January 1995 Chapter V: Benefit/Cost Analysis and Alternative Selection Benefit/Cost Analysis Optimization Example Given: A one-story, 2,500 SF slab-on-grade building with a first floor elevation of 6.0 NGVD is subject to coastal A Zone flooding (1 -yr = 2.0', 1 0-yr = 5.0', 50-yr = 7.0', 100-yr = 9.0', and 500-yr = 10.0'). Building replacement is estimated at $50/SF; contents replacement at $8/SF, and rental cost (displacement) at $ 1/SF. Alternative 1: Construct a 3-foot-high floodwall (9.0' NGVD) around the building. The floodwall has a 30-year useful life and project costs are estimated at $10,000 with an annual maintenance cost of $250. Floodwalls are considered effective to one foot belowtheir flood protection elevation. In this case, seepage and leakage concerns reduce the project effectiveness to 90% for floods reaching 6.0' NGVD; 85% at 7.0,' NGVD; 80%NGVD, and 0% at 9.0' NGVD and above (since the water elevation is the same both inside and outside the floodwall due to overtopping). Alternative 1 Results: Benefit/cost ratio of 1.03 indicates this project is beneficial to pursue. However, the homeowner is concerned that seepage and leakage will damage flooring and building contents (and result in a potentially expensive temporary relocation) and is therefore considering adding an interior drainage system (periphery drainpipe and sump pump system) to Alternative 1. Economic optimization can be used to indicate whether or not this design change would be cost-beneficial. Alternative 2: Construct an interior drainage system with the 3' floodwalI proposed in Alternative 1. New project costs are estimated at $15,000 with annual maintenance of $350. The drainage system improves project effectiveness to 100% at all flood depths up to and including 8.0' NVD. Alternative 2 Results: Benefit/cost ratio of 0.81 indicates the addition of an interior drainage system would not be a beneficial modification to Alternative 1. This results from the fact that the increased benefits (damages avoided) are not sufficient to support the additional construction cost and annual maintenance expenditures. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Select a Method SELECT A METHOD While benefit/cost analysis provides an indication as to whether or not a retrofitting alternative is cost-beneficial, it is not the sole parameter upon which retrofitting measures are selected. Occasionally, there will be more than one favorable alternative, or the designer will customize the retrofitting measure, either by combining several methods or varying the level of protection. Owner preference can also have an impact on sound economic analysis and make a less cost-beneficial alternative a more preferable choice. The cost of the retrofitting measure may be the pivotal factor in a homeowner-financed retrofitting project. Conversely, local code requirements may limit the use of a method preferred by the homeowner. In the final analysis, it is the owner who must be satisfied with the retrofitting alternative. Each of these factors (aesthetics, local code requirements, and hazards such as wind, earthquake, erosion, impact, and other forces) may affect the applicability of a specific retrofitting measure. The designer is advisedto considerthese factors along with the cost and benefit/cost ratio ofthe various alternatives (see Figure V-8). Factors Weighing on * PresentWorth of Benefits: This indicates the present Alternative Selection worth of annual damages avoided by the retrofitting alterna * Present Worth of tive. The designer should review this value in terms ofhis/ Benefits her expected benefit (threshold for damages to be avoided). * Total Project Cost * Benefit/Cost Ratio * TotalProject Cost: This represents costs requiredto * Technical Feasibility construct the retrofitting alternative. The designer * Need for Human shouldreviewthis value in terms of how the project Intervention suits the homeowner's budget. * Need for Annual Maintenance * Benefit/Cost Ratio: As discussed previously, this Figure V-8: Factors Weighing on value indicates whether analternative is cost-beneficial. Alternative Selection The higher the value, the more cost-beneficial the alternative. The designer should review the benefit/cost ratios for the retrofitting alternatives being considered. Fnnineprinn Princinles and Practices of Retrofittina Flood-Prone Residential Structures V -25 January 1995 Chapter V: Benefit/Cost Analysis and Alternative Selection o Technical Feasibility: The designermustjudge the technical solution(s) that best address the project objectives. * Aesthetics: This value reflects the owner's view on the way the retrofitting alternative fits in with the appearance of his/herhouse. * Human Intervention Requirements: This reflects the need for human intervention to operate the retrofit measure and the warning time required to conduct the required activity. * Annual Maintenance: This reflects the intensity of annual maintenance required by each retrofitting alternative. A preference scale or order of preference ranking can be utilized with the table presented in Figure V-9 to arrive at a subjective decision on the retrofitting method to be selected. The preference scale assigns numbers 0 to 10 to each alternative by factor, with 0 indicating not liked and 10 meaning liked a lot. The values assigned to the various factors for each alternative are totalled, and the alternatives with the highest total should be the optimal choices. The preference scale process can also be modified by weighting the decision factors to reflect the increased importance of any specific factor. For example, if total project cost were the predominant factor, the value (0-10) could be multiplied by a factor, for example, 2, which would double its contribution to the overall score, thereby reflecting its importance. Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Select a Method OwnerName: PreparedBy: Address: Date: PropertyLocation: Decision Factors Other PW Technical Human Annual Total Alternative Benefits Cost B/CRatio Difficulty Aesthetics InterventionMaintenance Score Prlevnreact-on ¢ A6 * '-3 i Impotnce "' 1.0 .~ ____ 0 WeightedScore' 8 5 6 8 = 45 Prefren e, 1. _ _ _ _ _ _ _ _ _ Preference_----------------------------- -----7-7_ Importance WeightedScore 2. Preference Importance WeightedScore 3. Preference Importance WeightedScore 4. Preference Importance WeightedScore 5. _ _ _ _ _ _ _ Preference Importance WeightedScore 6. Preference Importance _ ------------------------------------ WeightedScore Instructions: This matrix may be filled out by the designer in consultation with the homeowner. The objective of this matrix is to select an alternative for design from competing alternatives which had previously passed screening for technical feasibility and homeowner preference. For each alternative, enter the alternative name (i.e. 1A, 1B, 1C) and unweighted preference score (0-10) on the first row. A score of 0 indicates the measure is the least preferred in terms of the decision factor, while a score of 10 indicates the measure is the most preferred. A blank column is provided for any additional decision factor(s) which are being considered by the designer or homeowner. Based upon the relative importance of each decision factor to the designer and homeowner, develop and enter an importance factor (weighting amount) for each decision factor on the second row. Multiply the unweighted preference score by the importance factor (weighting amount) and enter the result on the third line. Total the first and third lines on the right hand column (Total Score). The preferred alternative is the one with the highest weighted score. Figure V-9: Preference Ranking Worksheet Engineering Principles and Practices of Retrofitting Flood-15roneResidential Structures V-27 January 1995 Chapter V: Benefit/Cost Analysis and Alternative Selection DETAILED COST ESTIMATING Previously, in Chapter III, we were able to utilize a unit cost (per square foot) for a specific retrofitting measure, such as elevating a wood-frame building on an open foundation and adding ancillary items for fill and landscaping, to arrive at a preliminary construction cost estimate. When and ifthe cost estimate is refined after the retrofit measure alternatives are further defined from a design standpoint, the costs of each may be found to differ from earlier estimates that were used to rank the retrofit alternatives. Ifthis difference in estimated cost is significant for a given alternative, the benefit/costratio for that alternative could be affected. Therefore, the designer/analyst may re-run the benefit/cost model for any alternatives affected in this way, which could result in a different ranking of potential retrofitalternatives. When the retrofitting measure is designed (as discussed in Chapter VI), the cost estimate can be refined by identifing and pricing all ofthe components ofthe retrofitting measure. For example, site preparation, building preparation, permitting, excavation and earthwork, foundation, concrete, reinforcing, framing, elevation, utility extension, connections, code upgrades, backfill, site stabilization, access/egress, landscaping, and interest costs can be estimated and then aggregated. Engineering Principles and Practices of RetrofittingFlood-Prone Residential Structures January 1995 Select a Method Cost estimate accuracy can be directly related to the level of detail in a quantity breakdown. Quantities or components not identified usually do not get estimated and may not be covered by any allowed-for contingency, resulting in less accurate estimates. Figure V-10, the Floodproofing Measure Compo nent Takeoff Guide, was developed to identify cost items typically found in the various retrofitting measures. However, every retrofitting application is unique and may include more of or fewer than the components listed. Floodproofing Measure Component Takeoff Guide Elevation Techniques * Site Preparation * Building Preparation * Elevation of Structure * Foundation Construction * Connection of Structure to New Foundation * Extension of Utility Systems * Required Code Upgrades * Exterior Finish Work * Interior Finish Work * Access and Egress * Site Grading and Stabilization * Landscaping Relocation Techniques * Preparation of Existing Site * Preparation of Existing Building • Preparation of the Route * Elevation of Structure * Transfer of Building to Transportable Frame * Moving Building * Preparation of New Site (Including Utilities) * New Foundation Construction * Transfer of Building to New Foundation * Connection of Utility Systems * Exterior Finish Work * Interior Finish Work * Access and Egress * Site Grading and Stabilization * Landscaping * Demolition of Old Foundation * Grading and Stabilization of Old Site * Route Modification Reversals Floodwalls * Site Preparation * Excavation * Construction of Floodwall * Closure Installation * Access and Egress * Drainage System Installation * Site Grading and Stabilization * Interior Area Finishing * Utility System Adjustment * Landscaping Levees * Site and Borrow Area Preparation * Earthwork * Drainage System Installation * Access and Egress * Site Grading and Stabilization Shields * Building Preparation * Shield Installation * Interior Drainage System * Utility System Modification Sealants * Building Excavation and Preparation * Sealant Application * Interior Drainage System * Utility System Modification Figure V-10: Floodproofing Measure ComponentTakeoffGuide Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: Benefit/Cost Analysis and Alternative Selection SOURCES FOR UNIT COSTS Once a detailed quantity takeoff has been completed, unit-cost information can be obtained for individual items from a variety of sources. These sources include: * local construction industry data collected from published indexes or solicited from several construction companies; i average nationwide construction cost data, available from various publications, that contain factors for adjusting the average nationwide costs to specific locations and present-day values; and * data collected by the FEMA Mitigation Directorate for areas ofthe United States that have recently experienced major flooddarnage. These unit costsmay haveto be adjusted to a specific geographical area by multiplying the FEMA unit costby a factor of the Bureau of Labor Wholesale Price Index (or other published cost index) for the subject community and the community for which FEMA has data. FEMA has observed post-disaster inflation due to material and labor shortages that has significantly impacted the costs of restoring flood-damaged houses. For example, the cost of materials and labor was 10% higher after the 1993 Midwest flooding than before the storm. In the extreme case (catastrophic disaster) such as Dade County, Florida, after Hurricane Andrew, the increase was 25%. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Select a Method Unit costs are adjusted for local conditions with the following computation: local FEMA (WPI loaIWPIFEMA) (OPD) where: UC local is the unit cost of a specific retrofitting measure componentat the location in question; UC FENMA is the FEMA unit cost for a specific retrofitting measure at a specific location; WPIFEMA is the wholesale price index or other published cost index forthe locality at which FEMA has unit price data; WPIlocal is the wholesale price index or other published cost index at the locality for which a unit cost is needed; and IPD is post-disaster inflation due to a shortage of skilled labor and limited availability of materials. It ranges from 100 percent to 125 perent, but is normally 11 0 percent. Formula V-14: Adjusting Unit Costs for Local Communities Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Chapter V: BenefitlCostAnalysis and Alternative Selection Once appropriate unit-cost information has been collected, the Floodproofing Measure Component TakeoffGuide (Figure V10) and the Detailed Cost Estimating Worksheet (Figure V- I 1) can be used to develop the detailed cost estimate. It is important to include the contractor's profit and a contingency item to cover unexpected costs. Owner Name:_ Prepared By: Address: Date: Property Location: Floodproofing Measure: (Describe Project Specifics) Estimating Item Quantity Unit Unit Cost ItemCost Subtotal Design Fee Contractor's Profit Subtotal Contingency Total FigureV-l 1: Detailed Cost Estimating Worksheet V-32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Select a Method At the completion of this chapter, the designer has determined flood and non-flood-related hazards; developed and evaluated retrofitting alternatives; and, in concert with the homeowner, selected a retrofitting measure that addresses the flooding problem. The next step, covered in Chapter VI, is to develop a detailed design of the selected retrofitting measure and produce construction documents. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures V -33 January 1 995 CHAPTER VI *7< ; s1 4;,; I , : ,0',9 0 I GENERAL DESIGN PRACTICES Featuring: Field Investigation Analysis of Existing Structure Design Construction I MM FIELD INVESTIGATION I ANALYSIS OF EXISTING STRUCTURE I DESIGN AND CONSTRUCTION Local Building Requirements Hazard Determination Documentation of [Existing Building Systems_ Homeowner Preferences | Structural Reconnaissance Footings and Foundation 1 Systems l Lateral Loads Vertical Loads | Relocation Dry Floodproofing Wet Floodproofing Elevation ] J Capacity vs. Loading Floodwalls Levees Chapter VI: General Design Practices Table of Contents Field Investigation .......................................... VI -3 Local Building Requirements .......................................... VI -3 Surveys .......................................... VI -3 Structure Survey .......................................... VI -4 Topographic Survey .......................................... VI -5 Site Utilities Survey .......................................... VI -7 HazardDeterminations ........................................... VI -9 Documentation offExistingBuilding Systems ............. ............................. VI -9 Homeowner Preferences .......................................... VI -14 HomeownerCoordination.......................................... VI -14 Maintenance Programs and Emergency Action Plans .......................................... VI -15 Analysis of Existing Structure ........................................... VI -16 Structural Reconnaissance .......................................... VI -16 Footings and Foundation Systems .......................................... VI -19 Footings .......................................... VI -20 Bearing Capacity .......................................... VI -21 Lateral Loads ........................................... VI -24 Vertical Loads .......................................... VI -25 Dead Loads .......................................... VI -26 Live Loads .......................................... VI -29 Roof Snow Loads ........................................... VI -29 Calculation of Vertical Dead, Live, and Snow Loads .......................................... VI -29 Capacity Versus Loading .......................................... VI -34 Load Combination Scenarios .......................................... VI -34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -i January 1995 Elevation Types of Residential Structures That Can Be Elevated ................... ..................... VI -E. 1 Houses over a Crawlspace ........................................ VI -E.2 Houses over Basements ........... VI- E. 11 Houses on Piles, Piers, or Columns ........................................ : VI -E. 16 Slab-on-Grade Houses ........................................ VI -E.16 Elevating a Slab-on-Grade Wood-Frame House ........................................ VI -E.17 Elevating a Slab-on-Grade Masonry Structure .. ...................................... VI -E.29 Heavy Building Materials/Complex Design ............. ........................... VI -E.29 Field Investigation Concerns ........................................ VI -E.31 Property Inspection and Existing Data Review ............. ........................... VI -E.3 1 Code Search ........................................ VI -E.31 Design........................................ VI-E.3 4a Elevation Sample Calculation ........................................ VI -E.31 Construction Considerations ........................................ VI -E.92 PriortoLifing anyHouse ......................................... VI -E.92 Slab-on-Grade House, Not Raising Slab With House ........................................ VI -E.92 Slab-on-Grade House, Raising Slab ........................................ VI -E.93 House over Crawlspace/Basement ........................................ VI -E.94 House on Piles, Columns, or Piers ........................................ VI -E.95 Relocation Step 1 -Selection of a House Moving Contractor .............. .......................... VI -R.3 Experience ........................................ VI -R.3 Financial Capability ........................................ VI -R.3 Professionalism and Reputation. .................................................... ........................... VI -R.3 Cost of Services ................... VI -R.4 VI -ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Step 2 -Analysis of Existing Site and Structure ..................................... VI -R.6 LiftingBeamPlacement ..................................... VI -R.7 Step 3 -Selection, Analysis, and Design of the New Site ..................................... VI -R.10 SiteAccess ..................................... VI -R.10 Penmits..................................... VI -R.10 Existing,Site ..................................... Step 4 -Preparation of the VI -R.11 Step 5 -Analysis and Preparation ofthe Moving Route .............. ....................... VI -R.12 Identify Route Hazards ..................................... VI -R.12 ObtainApprovals ..................................... VI -R.13 Coordinate Route Preparation ..................................... VI -R.13 Step 6 -Preparation of the Structure ..................................... VI -R. 14 DisconnectUtilities..................................... VI -R.14 Cut Holes in Foundation Wall for Beams ..................................... VI -R.14 Install Beams ..................................... VI -R.15 Install Jacks ..................................... VI -R.15 Install Bracing as Required ..................................... VI -R.16 Separate Structure from Foundation ..................................... VI -R.16 Step 7 -Moving the Structure..................................... VI -R.17 Excavate/Grade Temporary Roadway ..................................... VI -R. 17 Attach Structure to Trailer ..................................... -VI -R.18 Transport Structure to New Site ..................................... VI -R.21 Step 8 -Preparation of the New Site ..................................... VI -R.22 DesignFoundation................................................................................................... VI -R.22 DesignUtilities ..................................... VI -R.22 Excavation and Preparation of New Foundation ... .................................. VI -R.22 Constructionof Support Cribbing.. ...................................... VI -R.23 Construction of Foundation Walls ..................................... VI -R.24 Lower Structure onto Foundation ..................................... VI -R.24 Landscaping..................................... VI -R.25 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -iii January 1995 Step 9 -Restoration of Old Site ..................................... VI -R.26 Demolish and Remove Foundation and Pavement ................................ ...................VI -R.26 Disconnect and Remove All Utilities ................................ VI -R.26 Grading and Site Stabilization ................................ VI -R.27 Dry Floodproofing Dry Floodproofing ..................................... VI -D. 1 Emergency Operations Plan ..................................... VI -D.3 Inspection and Maintenance Plan ..................................... VI -D.4 Sealants and Shields ..................................... VI -D.5 Field Investigation ........................... ........................................................ "I " VI -D.12 ....................... Design ........... VI -D.14 Confirm Ability of Structure to Accommodate Dry Floodproofing Measures ............. VI -D. 14 Selection and Design of Sealant Systems ....................................................... VI -D.23 Coatings....................................................... VI -D.23 WrappedSystems ....................................................... VI -D.24 Brick Veneer Systems ....................................................... VI -D.28 Selection and Design of Shield Systems ....................................................... VI -D.32 Plate Shields ....................................................... VI -D.32 Construction Considerations for Sealants and Shields .................................. VI -D.49 Drainage Collection Systems .................................. VI -D.50 FrenchDrains .......................................................................................................... VI -D.52 Exterior Underdrain Systems ................. VI -D.53 InteriorDrain System ................. VI -D.56 VI -iv Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sump Pumps . VI -D.58 .................................... Types of Sump Pumps ..................................... VI -D.58 Ifiltration vs. Inundation ..................................... VI -D.59 Coordination with Other Floodproofing Methods ................. .................... VI -D. 59 Field Investigation ................................................................................................V I -D .60 .... Design ............... VI -D.63 BackwaterValves ......................................... ....................................................................... VI -D.72 FieldInvestigation. VI -D.74 Design.VI -D.74 EmergencyPower.VI -D.79 Field Investigation.................................................................................................... VI -D.81 Design .VI -D.82 Construction .VI -D.91 Wet Floodproofing Protection ofthe Structure .VI -W.2 Foundations .VI -W.2 Cavity Walls .................................................................................. ......................... VI -W.2 SolidWalls .VI -W.3 Design of Openings in Foundation Walls for Intentional Flooding of Enclosed Areas Below the FPE .VI -W.4 Use of Flood-Resistant Materials .VI -W.6 Building Operation and Maintenance Procedures and Emergency Preparedness Plans . VI -W.7 Flood Warning System .VI -W.7 Inspection and Maintenance Plan .VI -W.7 Flood Emergency Operation Plan .VI -W.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -V January 1995 Protection of Service Equipment .................................. VI -W.9 Relocation .................................. VI -W.9 Elevation .................................. VI -W.9 In-PlaceProtection.................................. VI -W.10 Field Investigation .................................. VI -W. 11 DesignOverview .................................. VI -W.14 Mechanical Systems .................................. VI -W. 15 Piping Systems .................................. VI -W. 16 Tanks .................................. VI -W. 16 Homeowner Coordination .................................. VI -W. 17 For ShieldingMeasures .................................. VI- W. 17 For Relocation Measures .................................. VI -W.17 Developing Design Details and Specifications .......... ........................ VI -W. 18 Verify Design with Homeowner .................................. VI -W. 18 Prepare Construction Documents .................................. VI -W. 18 Electrical Systems .................................. VI -W. 19 Central Heating System Alternatives .......................... VI -W.22 Gravity Furnaces ........................ VI -W.23 Forced Warm Air Furnaces ........................ VI -W.24 Hot Water Heating Boilers ........................ VI -W.25 Heat Pump Compressors ........................ VI -W.26 Central Cooling System ........................ . VI -W.26 Indoor Units ........................ VI -W.26 OutdoorUnits ........................ VI -W.27 Ductwork......................... VI-W.27 UnitaryA/C Systems ........................ VI -W.27 Ductwork Systems ........................ VI -W.27 Piping Systems ........................ VI -W.29 Fuel Supply/Storage Applications ........................ VI -W.30 In-Space Heating Equipment ........................ VI -W.3 1 Room Heaters and Wall Furnaces ........................ VI -W.3 1 Oil/Kerosene Heaters ........................ VI-W.31 Electric Heaters ........................ VI -W.32 Water Systems ........................ VI -W.32 Drinking Water Wells ........................ VI -W.32 On-Site Portion of Water Systems ........................ VI -W.33 VI -vi Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sewer Systems........................................................................................................ VI-W.34 On-Site Portion of Sewer Systems ................................ VI -W.34 SepticTanks............................................................................................................ VI-W.35 Telephone Systems ................................ VI -W.37 Cable TV Systems ................................ VI -W.38 Construction.......................................................................................................................VI-W .39 Electrical................................ VI -W.39 Mechanical..............................................................................................................VI-W.40 Floodwalls Types of Floodwalls ................................ VI -F.2 Gravity Floodwall ................................ VI -F.3 CantileverFloodwall ................................ VI -F.5 CounterfortFloodwall................................ VI -F.9 ButtressedFloodwall................................ VI -F.10 Field Investigation ................................ VI-F.11 Design ................................ VI -F.14 Floodwall Design (Selection and Sizing) ................................ VI -F.14 Sliding................................ VI -F.16 Overturning................................ VI -F.16 Pressure ................................ VI -F.16 Floodwall Design -Simplified Approach ............................................................. .VI -F.42 Floodwall Appurtenances .......................... VI -F.46 Floodwall Closures .......................... VI -F.46 Drainage Systems .......................... VI -F.55 Seepageand Leakage .......................... VI -F.60 Seepage Through the Floodwall .......................... VI -F.60 Seepage Under the Floodwall .......................... VI -F.61 Leakage Between the Floodwall and Residence ............... ................... VI -F.62 Architectural Details .................................. VI -F.63 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -vii January 1995 Maintenance Considerations ........................................... VI -F.70 Construction ........................................... VI -F.73 Levees Field Investigation........................................... VI -L. 1 Design........................................... VI -L.4 Standard Criteria ........................................... VI -L.4 Maximurn Settled Height of Six Feet .............. ............................. VI -LA Minimum Crest Width ofFive Feet ........................................... VI -L.5 Floodwater Side Slope of 1 Vertical on 2.5 Horizontal ........................................ 4 -L.5 Land Side Slope ........................................... VI -L.5 One Foot of Freeboard ........................................... VI -L.5 InitialPhases............................................. V. -L.6 Locate Utility Lines That Cross Under the Levee ............................................ V. -L.6 Provide"Cut-Off' forLevee Foundation Seepage........................................... VI -L.7 Identify Foundation Soil Type .............................................................................- VI L.7 Clay Foundation .......................... VI -L.7 Sandy Foundation .......................... VI -L.7 SeepageConcerns.......................... VI -L.8 Scouring/Slope Protection .......................... VI -L.9 InteriorDrainage .......................... VI -L.10 Maintenance.......................... VI -L.l I Cost .......................... VI -L. 12 Construction .......................... VI -L.14 Soil Suitability .......................... VI -L.14 CompactionRequirements.......................... VI-L.14 SettlementAllowance ............... VI -L.15 Borrow Area Restrictions ............... VI -L.15 Access Across Levee ............... VI -L. 15 VI -viii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 GENERAL DESIGN PRACTICES Chapter IV introduced the analyses necessary to quantify the flood-and non-flood-related hazards that control the design of a specific retrofitting measure. The objective of Chapter VI is to apply the anticipated loads developed in Chapter IV to the existing site/structure and design an appropriate retrofitting measure. This chapter covers the process of designing each retrofitting measure and developing construction details and specifications, providing the designer with tools to tailor each retrofitting measure to local requirements and homeowner preferences. Separate sections for elevation, relocation, dry floodproofing, wet floodproofing, floodwalls, and levees are I presented. The design of these retrofitting measures is a straightforward but technically intensive approach that will result in the generation of construction plans that may receive a building permit and mitigate potential flood and other natural hazards. This design process is illustrated in Figure VI- 1. Many elements of the design process (field investigation, homeowner coordination, maintenance considerations, and analysis of existing structure) are common to many of the retrofitting measures, warranting a general discussion of these elements. EngineeringPrinciples and Practices of Retrofitting Flood-Prone ResidentialStructures VI-1 Januarv 1995 Chapter VI: GeneralDesign Practices Field Investigation * Low Point of Entry Survey * Site Topography * Utility Locations * Local Building Regulations Homeowner * Hazard and Risk Determinations * Homeowner Preferences * Individual Preferences * Community Requirements Conceptual Design * Calculations and Analysis _~~~~~~~~~~~~~~~~~~~~~ * Type, Size and Location * Preliminary Cost Estimates I Revision * Construction Access Homeowner Coordination * Maintenance Considerations * Conceptual Design * Access Requirements * Emergency Operations Plan Final Design I * Calculations and Design I Agreement a Details and Specifications * Cost Estimates I Revision * Permits/Access Homeowner Coordination * Maintenance Considerations * Final Design * Access Requirements * Easements/Waivers Construction I Agreement * Contractor Selection a Construction Inspection * As-Built Documentation Homeowner Coordination I * Maintenance Program I * Emergency Operations Plan Figure VI-1: Design Process VI -2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation FIELD INVESTIGATION Detailed information must be obtained about the site and existing structure to make decisions and calculations concerning the design of a retrofitting measure. The designer should obtain the following information prior to developing retrofitting measure concepts for the owner's consideration: * local building requirements; * surveys; * final hazard determinations; * documentation of existing structural, mechanical, electrical, and plumbing systems; and * homeowner preferences. LOCAL BUILDING REQUIREMENTS Close coordination with the local building code official is critical to obtaining approval of a retrofitting measure design. The designer should review the selected retrofitting measure concept with the local building official to identify local design standards or practices that must be integrated into the design. This discussion may also identify, and provide an opportunity to resolve, issues where construction of the retrofitting measure may conflict with local building regulations. SURVEYS A detailed survey of the site should be completed to supplement the information gathered during the Low Point of Entry Determination (discussed in Chapter III) and to identify and Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -3 January 1995 ChapterVI: General Design Practices locate structure, site, and utility features that will be needed for the design ofthe retrofitting measure. Structure Survey The structure survey is a vertical elevation assessment at potential openings throughout the structure, whereby floodwaters may enter the residence. It may include: * basement slab elevation; * windows, doors, and vents; * mechanical/electricalequipmentand meters; * finished floor elevation of the structure; * drains and other floor penetrations; * water spigots, sump pump discharges, and other wall penetrations; * other site provisions that potentially may require flood protection such as storage tanks and outbuildings; and * the establishment of an elevation reference mark on or near the house. VI -4 Engineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Field Investigation Topographic Survey A detailed retrofitting design should not be developed without a site plan or map of the area. A state registered Professional Land or Property Line Surveyor can prepare a site plan of the area, incorporating the Low Point of Entry Determination information, as well as general topographic ___________________________ and physical features. The entire site and/or building lot should be mapped for design purposes. A typical topo- WI' graphic and site survey is shown in Figure VI-2. General surveying practices should be observed, but as a minimum Field surveys for design purposes the site plan should include: should be performed by a state registered Professional Land or Property Line Surveyor. * spot elevations within potential work areas; * one-foot or two-foot contours, depending on degree of topographic relief; * property lines, easements, and/or lines of division; * perimeter of house and ancilliary structures (sheds, storage tanks); DA-inpprinn Drnr:i of RPtrrnfittinn Flnoo-Prne Rsidential Structures VI -5 lti-R January 1995 Chapter VI: General Design Practices j Sample Topographic Survey I I I I I I I I North I'll0 I f R1 ai f|a I I I I I I /1I ,I I ~ ~ ~ ~/-_ DrnensOputI I --, -~t, ~ t _ca Grd. 29.70 st1 S.o --~~~~~3 D111 , -K , / Mr s1 5X hm 28'x 43 Edge ofRoad Avenue Ex 84' StormDrain Easement --------… , Ex 1O'Sanitary Sewer _ -_ __… 1I_ I _-Ex 15'Storm Drain II I I Plan View Mltt srald FFigure VI-2: Topographic and Site Survey VI -6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation * driveways, sidewalks, patios, mailbox, fences, light poles, etc.; * exposedutility service(meters,valves, manholes, etc).; * road or streets; * downspout locations; * trees, shrubs, and other site landscaping features; * building overhangs and chimney; * window, door, and entrance dimensions; * mechanical units such as A/C and heat pumps; and * otherappropriateflood data. Additionally, the site plan should extend at least 50 to 100 feet beyondthe estimatedconstructionwork area.The purpose of extending the site map beyond the estimated work limits is to insure that potential drainage and/or grading problems can be resolved. Construction site access for materials and equipment as well as sediment and erosion control measures may also have an effect on the adjacent work area. Local building code mapping issues should also be addressed. Site Utilities Survey As part ofthe field investigation, above-and below-ground site utilities should be identified. Above-ground utilities, such as Contact local utility companies power lines, manhole covers, electric meters, etc., can be regarding the location of under- located both horizontally and vertically on the topographic map. ground utilities before construction begins. Underground utilities, such as sanitary and storm drain lines, wells and septic tanks, and electric or gas service, will require DnPrnirino :nrl Drnxr.tinraof IRotrnfiftinnFonnd-PronenResidential Structures._..__._._ VI -7 I yIII IIII .. _ I .__.__ =fylt : III y ;:a1I wl r I-. I._.._. i~v~i -. -.-.-.._ January 1995 Chapter VI: General Design Practices .. .~~~~ ~ ~~ ~ ~ ~ ~ ~ ~ ~~~ an investigationthroughthe appropriateutilityagency. Local utility companies and county, municipal, and building code officials will be able to assist in the identification ofthe underground utilities. Sometimes a copy of the topographic map and area can be submitted to the utility agency, who will prepare a sketch oftheir underground service. A checklist of underground services includes: * water main and sanitary sewer pipes; * water and sanitary service pipes; * cable television; * gaslines; e storm drain pipes; * water wells; * electric service; * telephone cables; and * other local utility services. In some instances, exact horizontal and vertical locations ofthe utility service may be required. A smallhole, more commonly referred to as a test pit, can be dug to unearth the utility service in question. Typically this service is perforned by alicensed contractor or the utility provider. VI -8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation By identifying the utility services and units, provisions can be developed during the detailed design that will protect these utilities and keep them operational during a flood. Design provisions forutility relocation, encasement, elevation, anchor ing, and, in some instances, new service, can be prepared. HAZARD DETERMINATIONS The designer (with the homeowners) should review the risk determinations previously conducted in Chapter III and confirm If the design flood elevation is the flood protection design level and required height ofthe less than the 100-year flood retrofitting measure selected. Not merely a function of ex- elevation, the retrofitting measure pected flood elevation, freeboard, and low point of entry, this may violate FEMA standards. analysis should consider the protection of all components below Check with the local building official or the FEMA Regional the design elevation (i.e.below-grade basement walls and Office for clarification. associatedappurtenances). The analysis of flood-and non-flood-related hazards was presented in detail in Chapter IV. The designer should utilize the calculation templates presented there to finalize expected design forces. DOCUMENTATION OF EXISTING BUILDING SYSTEMS Documentation ofthe condition ofthe existing structure is an important aspect ofthe design of elevation, relocation, and dry and wet floodproofing measures. This topic was introduced in Chapter III as reconnaissance designed to provide preliminary information on the condition of an existing structure and its suitability forthe various retrofitting methods. Pnninaarinn Prinninipeand Prantircs ofRatrofittina Flood-Prone Residential Structures VI -9 January 1995 Chapter VI: General Design Practices As the design of a specific elevation, relocation, or dry and wet floodproofing measure is begun, the designer should conduct a 49 detailed evaluation of the type, size, location, and condition of Since the data sheets providedin theexisting mechanical, electrical, and plumbing systems. The this book are generalized for enclosed Mechanical, Electrical,Plumbing,and related Building residential housing applications Systems Data Sheet (Figure VI-3) can be used to document the and ask for information that may resultsofthis examination. not be applicable to a specific retrofitting measure, the designer should exercise judgment in collecting the information cited on the checklists. VI -10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation (Note: Collect only the data necessary for your project) Owner Name: Prepared By: Address: Date: Property Location: A. EXTERIOR UTILITIES AND APPURTENANCES Water O On-site well or spring O Public water system Water Purveyor's Name: Sanitary O On-site septic and drain field O Public sewerage Storm o On-site O Public sewerage Incoming Electrical Service O Overhead a Underground O Voltage E 120/240 volt 10 0 120/208 volt 10 O Direct Burial Size: O Service Entrance Cable Amps: O PVC Conduit o RGS Conduit Transformer #: E Power Co: Power Meter #: Contact: Estimated Transformer Rating: Fault Current Rating: Telephone Service Cl Company: a Overhead E Underground El Cable Pair El Pedestal E Grounded E Direct Burial Cable TV • Company: E Overhead E Underground# of channels: E PVC CATV #: E Direct Burial E RGS: Contact: Page 1 of 3 Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet Practicesof Retrofittina Flood-Prone Residential Structures FnninpprinnPrinrin1P an1nd VI -11 January 1995 Chapter VI:General Design Practices Other Utilities Ol Natural Gas Utility Company Name: Location of service entr ance: Meter Location: O LPG Utility Company Name: Location of gas bottle: How is tank secured? n Oil Oil Supplier: n Above ground tank O Underground tank Size gallons Location Vent terminal Elevation:_ feet or elevation above grade? feet Fill cap type: B. DOMESTIC PLUMBING Water El Location of service entrance Main service valve? E Yes Cl No Backflow preventer? VI Yes 0 No Type of water pipe El Copper Cl Iron E Plastic D Domestic water heater al Gas BTU/HR E Oil GAUHR E Other Specify units Size: gallons Location: E Sanitary Drainage Floor served? Fixtures below BFE El Yes El No Backwater valve installed in fixtures below BFE? E Yes 3 No Backwater valves needed (if none exist) E3 Yes C] No El Storm Drainage Basement floor drains connected? El Yes E3 No Is storm combined w/sanitary? El Yes E No C. HEATING SYSTEM Type E Central System El Space heaters Central System E Warm air El Hot water E Steam Warm Air Furnace Location: El Basement El 1st Floor 0a __floor El Attic Page 2 of 3 0 Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet (continued) VI -12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures .Iani iarv I 9.R Field Investigation Type: O Upflow Cl Downflow 0 Horizontal El Low Boy Fuel: C] Natural Gas E LPG O Electric E Coal E Wood Burner: E Atmospheric O Fan assisted Condensing: O Yes Cl No Venting: E Natural draft 0 Forced draft E Direct vent Air Distribution: O Gravity 13 Ducted E Sheet metal ductwork Cl Flexible, non-metallic runouts O Fiberglass ductboard O Location Air Outlets: a Floor E Low sidewall O High sidewall El Ceiling E 2nd floor Hot Water/Steam: Boiler: 0 Hot Water E Steam Location: 0 Basement E 1st Floor E __floor o Attic Fuel: 0 Natural Gas 0 LPG O Electric O Coal E Wood Terminal Units: 0 Baseboard 0 Radiators 0 Other In-Space Heating Equipment Gas E Room heater E Vented 0 Unvented E Wall Furnace E Conventional E Direct vent E Floor Furnace Oil/Kerosene: E Vaporizing oil pot heater E Powered atomizing heater E Portable kerosene heater Electric Heaters: E Wall E Floor O Toe space E Baseboard Radiant Heat: E Panels E Embedded fireplace E Portable cord and plug Solid Fuel Heaters: E Simple fireplace E Factory built E Radiant E Circulating E Freestanding Stoves: E Conventional E Advanced design E Fireplace insert El Pellet stove D. COOLING SYSTEM Type E Central E In-space Conditioners Central Systems E Split system A/C E Unitary A/C E A-Coil add-on E Split system heat pump Split Systems: Indoor unit locat ion: E Basement E 1st Floor E _floor E Attic Type: E Upfic)w 0 Downflow O Horizontal Air distribution: O Sheet metal ductwork O Fiberglass ductboard O Flexible non-metallic runouts Air outlets: E Floor 0 Low sidewall O High sidewall E Ceiling Outdoor unit location: In-space Air Conditioners: El Window air conditioners Page 3 of 3 El Ductless split systems Figure VI-3: Mechanical, Electrical, Plumbing and Related Building Systems Data Sheet (continued) Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -13 January 1995 Chapter VI: General Design Practices HOMEOWNER PREFERENCES A detailed discussion of homeowner preferences was presented in Chapter III. The designer should confirm the homeowner's preferences regarding: * retrofitting measure type, size, and location(s); * project design desires/preferences; o limitations on construction area; * estimated construction budget; and * potential future site improvements. Once the designer has collected the above-mentioned information, a conceptual design of the proposed retrofitting measure can be discussed with the homeowner. At this time the designer should also review and confirm coordination and future maintenance requirements with the homeowner to ensure thattthe selected retrofitting measure is indeed suitable. Homeowner Coordination Homeowner coordination is similar for each of the retrofitting methods and involves reviewing design options, costs, specific local requirements, access and easement requirements, maintenance requirements, construction documents, and other information with the homeowner and regulatory officials to present the alternatives, resolve critical issues, and obtain necessary approvals. VI -14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation Maintenance Programs and Emergency Action Plans Development of appropriate maintenance programs for retrofitting measures is critical to the continued success of retrofitting efforts. Refer to FEMA Technical Bulletin 3-93 Non-ResidentialFloodproofing- Requirementsand Certificationfor BuildingsLocatedin Special FloodHazardAreasin Accordance with the NFIP for additional guidance concerning minimum recommendations for Emergency Operations Plans and Inspection and Maintenance Plans. While this bulletinwas prepared for non-residential structures, it contains sound advice for the development of inspection, maintenance, and emergency operation plans. Design information presented in this chapter relates to field investigation, design calculations and construction details, and construction issues. Since many ofthe key elements in the field investigation phase were discussed above, only those issues that are critical to the design and successful construction of the particular retrofitting measure are included here. Engineering Principles and Practices of F letrofittingFlood-ProneResidential Structures VI -15 January 1995 Chapter VI: General Design Practices ANALYSIS OF EXISTING STRUCTURE The ability of an existing structure to withstand the addi tional loads created as a result of retrofitting is an important design consideration. Accurate reconnaissance of the foundation and estimates of the capacity of various struc tural systems are the first steps in the design of retrofitting measures. The objective of this analysis is to identify the extent to which structural systems must be modified or redesigned to accommodate a retrofitting measure such as elevation, relocation, dry and wet floodproofing, levees, or floodwalls. The steps involved in this analysisinclude: * structural reconnaissance; * determination of the capacity of the existing footing and a foundation system; V * analysis ofthe loads imposedby the retrofitting measure; and * comparison of the capacity of the existing structure to resist the additional loads imposedby the retrofitting measure. STRUCTURAL RECONNAISSANCE In order to determine whether a structure is suited to the various retrofitting measures being considered, the type and condition of the existing structure must be surveyed. Some structural systems are more adaptable to modifications than others. Some retrofitting methods are more suited for, or specifically designed for, various construction types. Ofthe retrofitting methods discussed, elevation, dry floodproofing, and relocation most directly affect a home's structure. Floodwalls and levees are designed to prevent water from reaching the house and thus should not have an impact on VI -16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of ExistingStructure the structure. Wet floodproofing techniques have a lesser impact on the structure due to equalization of pressures, and also require analysis of the existing structure. Several sources of information concerning the details of construction that were used in a structure include: * construction drawings from the architect, engineer, or builder. These are usually the best and most reliable resource for determining the structural systems and the size of the members; * information available from the building permits office; * plans of any renovations or room additions and a recent record of existing conditions; * contractors who have performed recent work on the house, such as plumbing, mechanical, electrical, or other kinds; * a home inspection report, if the home has been recently purchased. While these reports are not highly detailed, they may give a good review of the condition of the house and point out major deficiencies. If the aforementioned information is not available, the designer (with the permission of the owner) should determine the type and size of the critical structural elements. The structural reconnaissance worksheet provided at Figure VI4 can be used to document this information. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures .VI -17 January 1995 Chapter VI: General Design Practices - Owner Name: -Prepared By: - Address: Date: Prooertv Location: StructuralReconnaissance Worksheet Sketch and Description of Existing Structure: Condition Item Material Size (Excellent, Notes Fair,Noe Good, Unacceptable) l Footing Concrete Concrete Foundation Concrete Wall Masonry Brick Masonry Wood Frame Walls Masonry Metal Frame Wood Joist Floor System Beam Wood Truss Truss Roof System Rafter Wood Siding Exterior Brick Veneer Stucco Drywall Interior Plaster Finishes Wood .. Figure VI-4: Structural Reconnaissance Worksheet VI -18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Existing Structure FOOTINGS AND FOUNDATION SYSTEMS Elevating a house exposes it to The foundation system of ahouse (footings and foundation greater vertical loads from increasedwindloadingsand walls) serves several purposes. It supports the house by additionalweight,and horizontal transmitting the building loads to the ground, and it serves as an andshearloadsfrom increased anchor against uplift and against forces caused by wind, seismic, windforces. Figure VI-5illus-flooding, and other loads. Foundation walls (below grade) tratesthe variousloadsthat affect restrain horizontal pressures from adjacent soil pressures. The a foundation system. foundation system anchors the house against horizontal, vertical, and shear loads from water, soil, debris, seismic, snow, and wind hazards. Retrofitting measures such as elevation change the dynamics ofthe forces acting on a house. Snow Wind Forces 4 Loads Dead Loads Seismic Forces -ni /\BuoyancyLive Loads Impact Forces _i + ii Forces _ Soil Forces _ Flood Forces o 0 1 t t t t t $D 2IE°[~ I--O.oL o 20. 0 Figure VI-5: Foundation System Loading Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -19 January 1995 Chapter VI: General Design Practices M_ For linear foundation walls, the width of the footing is normally two times the thickness of the foundation wall. The depth of the footing is normally equal to the thickness of the foundation wall. Perimeter drainage systems may be used if the bearing soil is adversely affected by saturation. Often soils under bearing pressure will not become saturated due to low permeability. Each situation should be evaluated separately. 4. When older foundation systems (such as stone) are encountered, the designer should consult the local code on what procedures/ applications are allowable. The compressive strength of stone walls is so variable that professional testing and specialized expertise is usually required. Footings Footings are designed to transmit building loads to the ground and should be placed completely below the maximum frost penetrationdepth. Thesize of thefootingcan be determined by the formula below: A = P/Sb= ft2 where: A P Sbc is thebearingarea ofthe footing in square feet; isthe loadin pounds;and is the allowable soil bearing capacityin poundsper squarefoot. Formula VI-1: Determining Footing Size An existing footing should be checked to determine its maximum loading condition. Rearranging the above formula will provide the maximum load for the existing footing. xP=AS= lbs where: Pmax istheloadinpounds; A is the bearing area ofthe footing (in square feet); and S isthe soilbearing capacityin poundsper square foot. FormulaVI-2: Maximum Loadingof ExistingFooting VI -20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Existing Structure In conducting this computation, it is important to confirm the size and depth of the footing and bearing capacity ofthe soil to assure that the existing conditions meet current codes. In the absence of reliable information, excavation may be required to confirm the depth, size, and condition ofthe existing footing. The designer should also check the existing footing to ensure that it has a perimeter drainage system to prevent saturation of the soil at the footing. If one does not exist, the designer should consider including this feature in the design ofthe retrofit. Bearing Capacity The bearing capacity of an existing concrete masonry foundation wall can be estimated if the designer knows the size and grade ofthe block, using the following formula. . We=FcsA= lbs -w where: W. is the total weight per linear foot the wall will support; Fc is the bearing capacity ofthe masonry from Table VI-1; s is the slenderness ratio, which is computed from the height or length to thickness ratio ofthe member in question; and A is the cross sectional area per linear foot of wall. Formula VI-3: Bearing Capacity of an Existing Concrete Masonry Foundation Wall Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -21 January 1995 Chapter VI: General Design Practices At To limit the effects of slenderness on masonry walls, American ConcreteInstitute (ACI)530 provides maximum height or length to thickness ratios. Height or length is based on the location of the lateral support elements that brace the masonry and permit the transfer of loads to the resisting elements. Nominal wall thickness may be used for t . Table VL-2: Wall Lateral Support Requirements, provides maximum slenderness ratio values for bearing and non-bearing walls. The slenderness ratio, s, (which is less than 1.0) can be computed as follows: aCa0 s = 1.2 -H /37t = where: s is the slenderness ratio, a dimensionlessvalue; H1 t istheheightofthe unbraced foundation wall in inches; and isthethicknessofthe wallin inches. Formula VI-4: Slenderness Ratio By changingthevalueofthe bearingcapacityaccordingto the conditions identified on the site, the designer can determine the approximate weight that the foundation wall will support. If the type of block and mortar is unknown, the most conservative values should be used. Intrusive methods of investigation must be employed to determine footing depth, thickness, reinforce ment, condition, or drainage. Technology exists for investiga tion of walls using x-ray, ultrasound, and other methods; however, these methods may be too costly for residential retrofitting projects. VI -22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1 995 Analysisof Existing Structure The approximate bearing capacity of concrete and reinforced concrete materials may be quite variable due to regional differences in concrete mix, aggregate, reinforcing practices, and other factors. In general, the approximate bearing capacity of concrete/ reinforced concrete is substantially greater than masonry block: a conservative estimate ranges from 500 to 1,000 pounds per square inch. Additional information on the capacity and strength of concrete mixtures can be obtained from the American Concrete Institute (ACI) 318. Approximate Bearing Capacity Table VI-I for Masonry Materials Type of Stress and Masonry Type of Mortar Unit or Condition N S M Allowable stress, lb/in2 Compression, f., lb/in2 Brick, SW 300 350 400 Brick, MW 275 310 350 Brick, NW 215 235 290 Concrete block, grade A walls 85 90 100 Concrete block, grade B walls 70 75 85 Concrete block, grouted piers 90 95 105 Cut granite 640 720 800 Cut limestone, marble 400 450 500 Cut sandstone, cast stone 320 360 400 Rubble, rough, random 100 120 140 Glass block, min. 3 in. thick Exterior walls: Unsupported surface area < 144 ft2 Unsupported length < 25 ft Unsupported height <20 ft Interiorwalls: Unsupported surface area < 250 ft2 Unsupported length and unsupported height < 25 ft Table VI-2 Wall Lateral Support Requirements Maximum Construction SlendernessRatio (Iftwor h/tw) Solid or Solid 20 Bearing Grouted Walls All Other 18 Non-Bearing Exterior 18 Walls Interior 36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -23January 1995 Chapter VI: General Design Practices LATERALLOADS The ability ofexterior foundation walls and interior structural walls to withstand flood-related and non-flood-related forces is dependent upon the wall size, type, and material. Interior and For additional informationconcexterior walls are checked for failure from overturning, bending, For additional iformation concern-and shear (horizontal, vertical, and diagonal). If the stress ing the performance of various structuralsystems, refer to the U.S. caused by the expected loading is less than the code-allowable Army Corps of Engineers research stress for the expected failure mode, the wall design is accept- study entitled Flood Proofing able. Conversely, if the stresses caused by the expected Tests,August,1988. loadings are greater than the code-allowable stresses for the expected failure mode, the design is unacceptable and reinforc ing is required. Due to the large number of wall types and situations that can be encountered that would make a comprehensive examination of this subject unwieldy for this manual, only procedural and reference information for lateral load resistance is provided. The process of analyzing foundation and interior walls is outlinedbelow: Step 1: Determine the type, size, material, and location ofthe walls to be analyzed. Step 2: Using ACI 530 (Building Code Requirements for Masonry Structures) as a reference for masonry construction, determine the code-allowable overturning, bending, and shear stresses for the wall in question. ACI 530 has tables of allowable stress information for masonry structures based on physical testing. The American Plywood Association offers information on allowable loads in plywood shear walls. Watch for increased soil pressures due to overturning VI -24 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures -Iw--~--------o----J-- anuary____ ----------- 1995 January 1995 A'E* For additional information on loadingconditions for exterior and shear walls, refer to ASCE 7. i Analysis of Existing Structure in the wall. ACI 318 should be used for reinforced concrete walls, and ACI 318.1 for non-reinforced concrete walls. Lateral loads are distributed to the shear walls via the diaphragms of the floor or roof. Distribution is based upon relative stiffnesses ofthe walls. Use extreme care in the design of diaphragm-to-wall connections. Most codes require that an additional eccentricity (factor of safety) be considered in the location of the resultant ofthe lateral loads. Step 3: Compare the stresses caused by the expected loadings versus code-allowable stresses (capacities) for each wall being analyzed. If the stresses caused by the expectedloadingsare less than the code- allowable stresses, the design is acceptable; if not, reinforcement is required or another method should be considered. VERTICAL LOADS In addition to the loads imposed by floodwaters,othertypes of loads must be considered in the design of a structural system, such as building dead loads, live loads, snow loads, wind loads, and seismic loads (if applicable). Flood, wind, and seismic loads were discussed earlier in Chapters III and IV. This section deals with the computation of dead loads, live loads, and snow loads. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -25 January 1995 Chapter VI: General Design Practices Dead Loads Dead loads are the weight of all permanent structural and nonstructural components of a building, such as walls, floors, roofs, ceilings, stairways, and fixed service equipment. The sum ofthe dead loads should equal the unoccupied weight ofthe building. The weight of a house can be determined by quantifying the wall and surface areas and multiplying by the weights of the materials or assemblies. A list ofthe weights of some construction types is provided in Table VI-3. In additionto the weight ofthe structure, any furnishings and equipment located in the house must be added to the total. The worksheet provided at Figure VI-6 can be used to make a preliminary estimate of the weight of a structure. To use Figure VI-6, the designer should: Step 1: Determine the construction ofthe various components ofthe building, quantify them, and enter this information in the second column; Step 2: Look up the weight of these assemblies and enter that figure into the third column; Step 3: Multiply the quantities by the unit weights to obtain the construction component weights, and enter the result in the fourth column; Step 4: Add these component weights in column four to obtain an estimate ofthe total weight ofthe structure. Entertheresult in the box at the bottom of column four. VI -26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of ExistingStructure Table VI-3 Weights of Construction Types Weight, lb/ft2 Construction surfacearea Wood stud wall, 2x4, interior, '/-in drywall 2S 8 Interior, wood or metal 2x4s, plaster2S 19 Exterior, drywall; 4-in batt insul.; wood siding 11 Exterior, drywall; 4-in batt insul.; 4-in brick (MW) 47 Exterior,drywall; 4-in batt insul.; 8-in concrete block 60-65 Metal stud wall, 2x4, interior, %-indrywall 2S 7 Exterior, drywall; 4-in batt insul.; 1-in stucco 23 Metal stud wall, exterior, drywall; 4-in batt insul.; 2-in drywall 18 Exterior, drywall; 4-in batt insul.; 3-in granite or 4-in brick 55 Plaster, per face, wall, or ceiling, on masonry or framing 8 Ceramic tile veneer, per face 10 Masonry wall, 4-in brick, MW, per wythe 39 4-in conc. block, heavy aggregate, per wythe 30 8-in conc. block, heavy aggregate, per wythe 55 Glass block wall, 4-in thick 18 Glass curtain wall 10-15 Floor or ceiling, 2x10 wood deck, outdoors 8-10 Wood frame, 2x1 0, interior, unfinished floor; drywall 8-10 ceiling Concrete flat slab, unfinished floor; susp. ceiling 80-90 Concrete pan joist (25 in o.c., 12-in pan depth, 3-in 90-100 slab), unfinished floor; susp. ceiling Concrete on metal deck on steel frame, unfinished floor; 65-70 susp. ceiling Finished floors, add to above: Hardwood 3 Floortile 10 1/2-in terrazzo 25 Wall-to-wall carpet 2 Roof,sloping rafters or timbers, sheathing; 10-in batt insul.; 12-15 %/2-in drywall Built-up5-ply roofing, add to above 6 Metal roofing, add to above 3-4 Asphalt shingle roofing, add to above 4 Slate ortile roofing, '/4-in thick, add to above 12 Wood shingle roofing, add to above 3-5 1 Insulation, batt, per 4-in thickness 0.17 Insulation, rigid foam boards or fill, per inch thickness Stairways: Concrete 80-95 Steel 40-50 Wood 15-25 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -27 January 1995 Chapter VI: General Design Practices Owner Name: Prepared By: Address: Date: Property Location: BuildingWeight Estimating Worksheet Construction Type Surface Weight (Ibslsf) of Weight (1) Area (2) Surface Area (3) Component (4) Walls Exterior Interior Floors First Second Attic Roof Special Items Fireplace* Chimney* StructureWeight Furnishings Total Weight Figure VI-6: Building Weight Estimating Worksheet *Do not include if chimney/fireplace has a separate foundation. VI -28 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of Existing Structure Live Loads Live loads are produced by the occupancy of the building, not Check local codes for guidance on including environmental loads such as wind loads, flood loads, acceptable live loads. In the snow loads, earthquake loads, or dead loads. For residential absence of code information use one- and two-family dwellings, a typical floor live load is a ASCE 7. uniformly distributed load of 40 pounds per square foot. LL=ALo lbs where: LL is the live load in pounds; A is the area of each floor of the residence in square feet; and Lo istherminimumuniformlydistributed live load in pounds per square foot. Formula VI-5: Calculation of Live Load Roof Snow Loads The roof snow load varies according to the geography, roof slope, and thermal, exposure, and importance factors. Local building codes should be consulted to find the snow load and how to apply it to the structure. Take particular care to account for drift and unbalanced snow loads. If no local code is available, the designer should refer to ASCE 7 for this information. In areas of little snowfall, codes may require a minimum roof snow load. Calculation of Vertical Dead, Live, and Snow Loads Dead, live, and snow loads act vertically downward and are carried by the load-bearing walls or the columns to the foundation system. The load-bearing walls support any vertical load in addition to their own weight. The amount ofthe dead load Engineering Principles and Practices olf Retrofitting Flood-Prone Residential Structures VIA 29 January 1995 Chapter VI:General Design Practices carried by a wall or column is calculated based on the partial area ofthe roof and floor system (tributary areas) that are supported by that wall or column plus its own weight (self weight). The tributary areas are illustrated in Figures VI-7 and VJ-8 and determined as follows: For the load-bearing walls, a one-foot-widestrip of floor or roofperpendicularto the floorjoists orrooftrusses multiplied by halfthe span lengthofthejoist ortruss. Strip width is the same dimension as the joist or truss spacing. I-I I Is=° o A = 1w/2= ft2 where: A. is thewall tributary areain square feet; I is the length of the wall in feet; and w is the span length between walls or the wall and center girder in feet. Fornula VI-6: Calculationof Tributary Area for Load-bearing Walls VI -30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of ExistingStructure b o-ExteriorWallTributaryArea TrbutaryArea _________ ii~~~~~~~~~~ Figure VI-7: Column Tributary Area Figure VI-8: Wall/Girder Tributary Area A = I(a+b)/2 = ft2 g ,where:Ag isthecentergirdertributaryarea in square feet; 1 is the length ofthe wall in feet; and a+b is the span length between the center girder and walls in feet. FormulaVI-7: Calculationof Tributary Area for Center Girder * For columns the tributary area is the area bounded by imaginary linesdrawn halfway between the column and the adjacent load-bearing wall or column in each direction. At = (w/2)(112) = -ft2 where: At is the columntributary area in square feet; I is the length ofthe wall surrounding the column in feet; and w is the span length between walls surrounding the column in feet. I Formula VI-8: Calculationof Tributary Area for Columns -31 VI -31 Engineering Principlesand Practices of Retrofitting Flood-Prone Residential Structures ; ~~VI January 1995 Chapter VI:General Design Practices To calculate the loads, follow the steps below: Step 1: Inspect the roofand the floor construction to identify load-bearing walls. Mark the direction, the span length, and the supportingwalls or columns forthe roof trussesand floorjoists. Step 2: Calculate the roof and the floor tributary areas for each load-bearing wall and column. Step 3: For each load-bearing wall and column, multiply the tributary areas by the dead, live, and snow loads to find the total loads. coociI=c.II U TLdis= (DL + LL + SL) At=, lbs where: TLdis is the total dead, live, and snow loads acting on a specific wall or column in pounds; DL is the dead load in pounds per square foot (from Figure VI-6); LL is the live load in pounds per square foot (from Formula VI-5); SL is the snowloadin poundsper square foot (from code); and At is the tributary area ofthe wall or column in square feet (from Formulas VI-6 and VI-8). (When analyzing walls use Awinstead of At.) Fonnula VI-9: Calculation of Wall/Column Loads VI -32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 . Analysis of ExistingStructure Step 4: Calculate the selfweight of the wall or column. Add any overbearing soil and foundation weight to the total. This information can be taken from the calculation template shown in Figure VI-6. E-I13 _ ,,01 SW=SAWU= Ibs where: SW is the self weight ofthe component in pounds; SA is the section area of the component in square feet; and Wu is the unit weight of the componentin pounds per squarefoot of surface. FormulaVI-10: Calculationof the SelfWeight of the Wall! Column Step 5: Add all the above calculated loads to find the load carried by the wall or column to the foundation or footing. -1 100a 1001 F-I TL=SW+TLdis = lbs where: TL is the total load carried by the wall or column to the footing or foundation in pounds; SW is the self weight ofthe component in pounds; and TLdis is the total dead, live, and snow loads acting on a specific wall or column in pounds. Formula VI-11: Calculation of Total Load Carried by the Wall or Column to the Footing or Foundation VI -33 V-33 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures ;~~ V January 1995 Chapter VI: General Design Practices CAPACITY VERSUS LOADING The next step is to examine the capacity ofthe existing founda tion component or system versus the expected loading from a combination of dead, live, flood, wind, snow, and seismic loads. This analysis willprovide an initial estimate ofthe magnitude of foundation modifications necessary to accomplish an elevation or relocation project. Model building codes (BOCA, ICBO, SBCCI, CABO) require the analysis of a variety of loading conditions and then base the capacity determination on the loading condition that presents the most unfavorable effects on the foundation or structural member concerned. It is the purpose of the load combinations to identify critical stresses in structural members (or nonstructural members) and w critical conditions used to design the support system. Since Designers should refer to ASCE 7-every conceivable situation cannot be covered by standard load 95 when conducting load combina-cases, soundengineeringjudgmentmust be used. tion analysis. Load Combination Scenarios ASCE 7-95 prescribes how to analyze flood loads in concert with other loading conditions. This guidance involves the use of two methods-allowable stress design and strength design. In the case of allowable stress design, design specifications define allowablestressesthat maynot be exceededby loadeffects due to unfactored loads, that is, allowable stresses contain a factor of safety. In strength design, design specifications provide load factors, and, in some instances, resistant factors. The analysis of loading conditions may be checked using either method provided that method is used exclusively for proportioning elements of tat construction material. The designer VI -34 Enaineerina Princinles and Practices of Petrofittinm FInnr.Prmna Radv4antial QStnrtmn~a January 1995 Analysis of ExistingStructure should consultASCE 7-95 for guidance in analyzing the multi- hazard loading conditions described below: The following symbols are used in defining the various load combinations. D Dead Load E Earthquake Load F Load due to fluids with well defined pressures and maximumbeights F FloodLoad H Load due to weight and lateral pressure of soil and water in soil L Live Load Lf Roof LiveLoad .~~~~~~~~~~~ R RainLoad S SnowLoad T Self-Straining Force W WindLoad Thesesymbolsare based upon informationfromASCE 7-95 but do not match exactlyas several symbolshadto be revised to accommodate symbols already used in this manual. Refer to ASCE 7-95 for clarification and additional information. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -35 January 1995 Chapter VI: General Design Practices STRENGTH DESIGN METHOD When combining loads using the strength design methodology, structures, components, and foundations should be designed so that their strength equals or exceeds the effects ofthe factored loads inthe followingcombinations: 1. lAD 2. 1.2(D+F+T) +1 .6(L+H) + 0.5(L or S or R) 3. 1.2D+ 1.6(LrorSorR)+(0.5Lor0.8W) 4. 1.2D+ 1.3W+0.5L +0.5(L orS orR) 5. l.2D+ .OE+0.5L+0.2S 6. 0.9D+ (1.3W or 1.OE) Exception: The load factor on L in combinations (3), (4), and (5) shall equal 1.0 for garages, areas occupied as places of public assembly, and all areas where the live load is greater than 100 lb/ft2 (pounds force per square foot). Each relevant strength limit state shall be investigated. Effects of one or more loads not acting should be investigated. The most unfavorable affects from both wind and earthquake loads should be investigated, where appropriate, but they need not be considered to act simultaneously. The structural effects of Flood (F.) should be investigated in design using the same load factors as used for L (live load) in the basic combinations of 2 and 4. The structural effects of Fmshould also be included when investigating the overturning and sliding in the basic combination 6 using a load factor of 0.5 when wind also occurs and 1.6when acting alone. VI -36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Analysis of ExistingStructure ALLOWABLE STRESS METHOD When combining loads using the allowable stress method, the loads should be considered to act in the following combinations, whichever produces the most unfavorable effect on the building, foundation; or structural member being considered. 1. D 2. D+L+F+T+(LrorSorR) 3. D+(WorE) 4. D+L+(LrorSorR)+(WorE) The most unfavorable effects from both wind and earthquake loads should be considered, where appropriate, but they need not be assumed to act simultaneously. Buildings and other structures should be designed sothat the overturning moment due to lateral forces (wind or flood) acting singly or in combina tion does not exceed two-thirds ofthe dead load stabilizing moment unless the building or structure is anchored to resist the excess moment. The base shear due to lateral forces should not exceed two-thirds of the total resisting force due to friction and adhesion unless the building or structure is anchored to resist the excess sliding force. Stress reversals should be accounted for where the effects of design loads counteract one another in a structural member orjoint. Analyzing the existing structure's capacity to resist the expected loads is sometimes a long and tedious process, but it must be done to ensure that the structure will be able to withstand the additional loadings associated with various retrofitting measures. The objective ofthis analysis is to verify that: * the existing structure is able to withstand the anticipated loadings due to the retrofitting measure being considered; n...4, :..I.. ..... --- --, oo,-,#;*tinr^ Clnr-Prnn PReirdentiai Structires VI -37 Engineeringyrlncip1UbanU r19A9U5O ul "UMAULMU I -I J January 1 995 ChapterVI:General Design Practices • the existing structure is unable to withstand the anticipated loadings due to the retrofitting measure being considered and requires reinforcement or other structural modification; and/or e the retrofitting measure should be eliminated from consideration. Using the information presented herethe designer should be able to conduct the analyses to implement the stated objective and identify the measures/modifications that must be designed. VI -38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Table of Contents Types of Residential Structures That Can Be Elevated .................. ...................... VI -E. 1 Houses over a Crawlspace ........................................ VI -E.2 Houses over Basements ........................................ VI -E. 11 Houses on Piles, Piers, or Columns ........................................ VI -E. 16 Slab-on-GradeHouses ........................................ VI -E. 16 Elevating a Slab-on-Grade Wood-Frame House ........................................ VI -E. 17 Elevatinga Slab-on-GradeMasonryStructure......................... ............... VI -E.29 Heavy Building Materials/Complex Design ............. ........................... VI -E.29 FieldInvestigationConcerns........................................ VI -E.31 Property Inspection and Existing Data Review ................ ........................ VI -E.3 1 Code Search ........................................ VI -E.31 Design........................................ VI -E.34 Elevation Sample Calculation ........................................ VI -E.48 Construction Considerations ................................................................................................ VI -E.92 PriortoLifing anyHouse ................................... VI -E.92 Slab-on-Grade House, Not Raising Slab With House .................... .............. VI -E.92 Slab-on-Grade House, Raising Slab .................................. VI -E.93 Houseover Crawlspace/Basement.................................. VI -E.94 House on Piles, Columns, or Piers................................... VI -E.95 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -E.i January 1995 ELEVATION One of the most common of all retrofitting techniques is to raise an entire existing super structure above the desired flood protection elevation. When properly done, the elevation of a house places the living area above all but the most severe floods. In general, the steps required for elevating a building are essentially the same in all cases. A cradle of steel beams is inserted under (or through) the structure; jacks are used to raise both the beams and structure to the desired height; a new, elevated foundation for the house is constructed; utility systems are extended and modified; and the structure is lowered back onto the new foundation and reconnected. While the samebasic elevationtechniques are used in all situations, the final siting and appearance of the house will depend on the final elevation and type of foundation used. However, the actual elevation process is only a small part of the whole operation in terms of planning, time, and expense. The most critical steps involve the preparation of the house for elevation and the construction of a new, adequately elevated foundation. The elevation process becomes even more complex with added weight, height, or complex design or shape of the house. Brick or stucco veneers may require removal prior to elevation. Building additions may need to be elevated independently from the main structure. TYPES OF RESIDENTIAL STRUCTURES THAT CAN BE ELEVATED The elevation of houses over a crawlspace; houses with basements; houses on piles, piers, or columns; and houses -I,' on a slab-on-grade are examined here. In each of these situations, the designer must account for multiple (non- Figures VItEh throughVo-E5 flood-related) hazards, such as wind and seismic forces. The onextendedsolidfoundation various methods utilized to elevate different home types are walls.Subsequentfiguresfor illustrated in the pages that follow, providing the designer with variouselevationtechniqueswill an introduction to the design of these measures. include only those illustrations unique to that technique. Enaineerina Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.1 January 1995 Chapter VI: General Design Practices Elevation ' F -I Information on the design of foundation wall openings and adjustment of existing utility systems can be found in the Wet Floodproofing section of Chapter VI. HOUSES OVER A CRAWLSPACE These are generally the easiest and least expensive houses to elevate. They are usually one-or two-story houses built on a masonry crawlspace wall. This allows for access in placing the steel beams under the house for lifting. The added benefit is that since most crawlspaces have low clearance, most utilities (heat pumps, water heaters, air conditioners, etc.) are not placed under the home; thus the need to relocate utilities may be limited. Houses over a crawlspace can be: * elevated on extended solid foundation walls (see Figures VI-El through VI-E5); or * elevated on an open foundation such as masonry piers (see Figures VI-E6 through VI-E8). VI-E.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Figure VI-El: Existing Wood-Frame Residence with Crawlspace Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.3 January 1995 Chapter VI: General Design Practices Elevation 1. Ltting Beam 2. Existing Masonry Foundation 3. HydraulIc Jack 4. Lateral Support Beams Figure VI-E2: Install Network of Steel "I" Beams Vi -E.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated 1. Excavated Area 2. Existing Crawlspace 3. Existing Concrete Footing 4. Extending Masonry Foundation Wall 5. Openings for Floodwater Figure VI-E3: Lift Residence and Extend Foundation Walls; Relocate Utility and Mechanical Equipment Above Flood Level Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.5 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E4: Raising a Wood-Frame-Over-Crawlspace Structure VI -E.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated 1. Existing Wood Floor System 2. Heightened Crawispace 3. Openings for Floodwater Figure VI-E5: Set Residence on Extended Foundation and Remove "I" Beams Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.7 January 1995 Chapter VI: General Design Practices Elevation 1. Existing Foundation to Remain 2. New Reinforced Masonry Piers 3. New House Support Beams Figure VI-E6: Install Network of Steel "I" Beamns VI -E.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Typesof Residential Structures That Can Be Elevated Figure VI-E7: Raising a Wood-Frame-Over-Crawlspace Structure on Piers Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.9 January 1995 Chapter VI: General Design Practices 0 Elevatlon 1. NowReinforced Masonry Piers 2. ExistingFoundation 3. New Ieoated Reinforced Masonry Pier and Fooling Figure VI-ES: Set Residence on Reinforced Piers VI -E.10 Enaineedna Princioles and Practices of Ratrofittinn F~nnr1-PmnnaRaqirlantical *n wriinaga _I,,_ __..____..._..,"_J 1995 ,,,...... _..... January 1995 Typesof Residential Structures That Can Be Elevated FEMA's post- and pre-FIRM requirements do not allow basements below the Base Flood Elevation (BFE) for substantially damaged/improved and post- FIRM applications. For more information on what retrofitting measures are allowable under FEMA guidelines, refer to Chapter II, Regulatory Framework. HOUSES OVER BASEMENTS These houses are slightly more difficult to elevate because their utilities are usually in the basement. In addition, basement walls may have been extended to the point where they cannot structurally withstand flood forces. Houses over basements can be: * elevated on solid foundation walls by creating a new masonry-enclosed area on top of an abandoned and filled-in basement (see Figures VI-E9 through VI-E 10); or * elevated on an open foundation, such as masonry piers, by filling in the old basement (see Figures VI-El I and VI-E12). Engineering Principles and Practices of IRetrofitting Flood-Prone Residential Structures VI -E.1I January 1995 Chapter VI: General Design Practices Elevation 1. Existing Wood Floor and Joists 2. Existing Woodframe 3. Now Windows 4. Now Masonry Enclosed Area 5. Openings for Floodwater Figure VI-E9: Relocate Utility and Mechanical Equipment Above Flood Level VI-E.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Existing floor system 1V I This area maybe used for bilding access, parking, and storage only New reinforced concrete slab se existin cntinuous concrete footing. i codeiss tisTied. Al 100-year lood level First floor -Sole plate New 8" masonryblock wall _MEM" Required I ,:' "moroo at I | Figure VT-E IO: Creation of a New Masonry Enclosed Area on Top of an Abandoned Basement Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.13 January 1995 Chapter VI: General Design Practices Elevation w~I ExistingFor sM IOraor Rood I FirstNow t-Sd6 Pkf I A ~~- b Ne~wMKPW bem -NoW hwe beam po It-1E New I fod Now Minhrod masonry pierandfooing remnfVrc masonrypiw _ ii:~~~rw I I I Us"xisingcontinuousconcrobfooting, I ifcodeis slatife 4v I I Figure VT-EI1: Creation of a New Masonry Enclosed Area on Top of an Abandoned Basement (Piers) VI -E.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Figure VI-E12: Set Residence on Reinforced Piers Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.15 January 1995 Chapter VI: General Design Practices Elevation HOUSES ON PILES, PIERS, OR COLUMNS The process of elevating a house on piles, piers, or columns is slightly more complex in that temporary relocation of the house may be part of the elevation process. With the use of this type of foundation, the house may need to be lifted off the existing foundation and temporarily relocated on-site. The existing foundation is then removed and/or reconstructed, and the house is reset on the new foundation. However, raising the home above the working area may provide sufficient room to auger pier and column foundations and to jet pile foundations. SLAB-ON-GRADE HOUSES These houses are the most difficult to raise in that if the slab is to be raised with the house, a trench must normally be dug under the house to provide a space for inserting lifting beams. However, intrusive techniques that place beams through the structural walls have proved to be successful in elevating slab-on-gradehomes, as well. If the existing slab is to remain in place, then the house must be detached from the slab, the structure raised separately from the slab, and a new floor system built, along with an elevated foundation. While slab-on-grade houses may be the most difficult to raise, a number of elevation options exist with regard to raising the structure with or without the slab and using a first floor composed of wood or concrete. The various alternatives include: VI -E.16 Enaineenna Principles and Practices of Retrofittinn Floond-PrnnaRaeidential Structures v-Iw ___. .__ -W w_ Ju 19 5 _.......w al w %-- January 1995 Types of Residential Structures That Can Be Elevated Many of the techniques that require interior home modifications are applicable only to structures that have suffered extensive interior damage. For additional information, refer to FEMA publications entitled Technical Information on Elevating Substantially Damaged Residential Structures in the Midwest, August 24, 1993, and Technical Information on Elevating Substantially Damaged Residential Buildings in Dade County, Florida, January 29, 1993. Elevating a Slab-on-Grade Wood- Frame House * Elevating a slab-on-grade wood-frame house without the slab, using a new first floor constructed of wood trusses (see Figures VI-E13 through VI-E17); * Elevating a slab-on-grade wood frame house without the slab, using a new first floor constructed of a concrete slab on top of fill (see Figures VI-E1 8 through VIE20); * Elevating a slab-on-grade wood frame house with the slab intact (see Figures VI-E2 1 through VI-E23); Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.17 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E13: Existing Slab-on-Grade Wood-Frame Residence VI -E.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated 1. Lateral Support Beam 2. Concrete Slab 3. Hydraulic Jack 4. Lifting Beam I Figure VI-E14: Install Steel "I" Beam Network and Prepare to Lift Walls Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.19 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E15: Lift Residence and Extend Masonry Foundation Wall; Relocate Utility and Mechanical Equipment above Flood Level VI -E.20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated N wS"wall asb-lor * - Ne tn jobt -100yFir floodr > __ ~~~~~~~~~~~~~~ ~~Forfloodwtr ENotwi8"tmasonry 1 blook wall g~~~~~~~~~~~~~~~~Eitn Sle Existingslab concrete~ ~ ~ ~ ~ lat ground Use existing continuous concretefooting, if codeis satisfied. Figure VI-E16: Raising a Slab-on-Grade Wood-Frame Structure Without the Slab Enaineerina PrinCiplesand Practices of Retrofittina Flood-Prone Residential Structures VI -E.21 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E 17: Set Residence on New Foundation and Remove "I" Beams VI -E.22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Figure VI-E 18: Lift Residence and Extend Masonry Foundation Wall; Relocate Utility and Mechanical Equipment Above Flood Level Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.23 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E19: Raising a Slab-on-Grade Wood-Frarne Structure Without the Slab Intact VI -E.24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated 1. New Concrete Slab 2. Extended Masonry Walls 3. Existing Slab Figure VT-E20: Set Residence on New Foundation and Remove "I" Beams Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.25 January 1995 Chapter VI: General Design Practices Elevation Figure VI-E2 1: Excavate Under Existing Slab and Install Network of Steel "I" Bearns VI -E.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Figure VI-E22: Raising a Slab-on-Grade Wood-Frame Structure With the Slab Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi-E.27 January 1995 Chapter VI: General Design Practices Elevation |, Existing Slab Elevated |2. Openings for Floodwater Figure VI-E23: Set Residence on New Foundation and Remove "I" Beams Vi -E.28 Engineering Principle is and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Residential Structures That Can Be Elevated Elevating a Slab-on-Grade Masonry Structure * Elevating a slab-on-grade masonry structure with the slab intact; * Elevating a slab-on-grade masonry structure without the slab using a first floor constructed of a concrete slab on top of fill; * Elevating a slab-on-grade masonry structure without the slab using a first floor constructed of wood framing; * Installation of an elevated concrete slab within an existing masonry structure; * Installation of an elevated wood-frame floor system within an existing masonry structure; * Creation of a new masonry livable area on top of an existing one-story masonry structure; and, * Creation of a new wood-frame livable area on top of an existing one-story masonry structure. HEAVY BUILDING MATERIALS/ COMPLEX DESIGN The elevation process becomes even more complex with added weight, height, or complex design of the house. Brick or stucco veneers may require removal prior to elevation. Combination foundations (i.e., slab-on-grade and basement) should be evaluated jointly and separately and the worst case scenario utilized for design purposes. Building additions may need to be elevated independently from the main structure. Due to the extreme variability of structural conditions, a structural engineer should evaluate the suitability of lifting this type of house. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.29 January 1995 Chapter VI: General Design Practices Elevation The entire elevation design process is discussed here and then illustrated with a detailed example of the design for a crawlspace home (Figure VI-E24). Elevation Design Process Field Investigationand CodeSearch CalculateGravityLoads (Dead, Live, Snow, andVerticalFlood Loads) CalculateLateralLoads I (Wind,Seismic,and Flood-Related) 'I, Check ExistingStructurefor Loading Truss to Wall Connection PlywoodRoof Diaphragm Upper LevelWalls FloorDiaphragm I +TDesign Strengthening 0NotOK Not OK 40__R OK CuheckExisting I Foundationfor Leadinis HDesign Strengthening Not OK Not OK Select Another Measure . ... .. .. Design NewFoundationWalls Design NewTop of FoundationWall Connection DesignSill Plate Connections DesignNew Access k Design Utility Extensions SpecifyAdditionalInsulation Figure VI-E24: Design Process for an Elevated Structure VI -E.30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation Concerns FIELD INVESTIGATION CONCERNS PROPERTY INSPECTION AND EXISTING DATA REVIEW During the field investigation, the designer should inspect the property and review existing data to confirm the applicability of the selected alternative and to confirm specific design guidance such as the height of elevation and type of foundation to be utilized. The designer should utilize the guidance presented in the beginning of this chapter where detailed information and checklists for the collection of information on the Structural, Mechanical, Plumbing, and Electrical Systems was presented. Much of the data has been discussed previously in Chapters III and IV. At a minimum, the designer should collect information on the following checklist (Figure VI-E25). CODE SEARCH During the field investigation the designer should also conduct a search of local floodplain ordinances, building codes, restrictions to deeds, restrictions in subdivisions, zoning regulations, and state building codes. Included with this search, a visitwith the local building official should be planned to determine any special requirements for the locality. During the code search,the following should be determined: * floodplainordinance; * building code in effect; * design wind speed; * design seismic zone; Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.31 -January 1995 Chapter VI: General Design Practices Elevation * ground snow loads; * frost depths; * restrictions on height (overall building, portions of building relative to materials in use, allowable height/ thicknessratios); and * restrictions on foundations. VI -E.32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation Concerns Owner Name: Prepared By: Address: Date: Property Location: Elevation Field Investigation Worksheet U Does site topography data cover required area U Yes U No Additional data required IJ Any construction access issues? U Site and building utilities identified? IOYes U No Potential utility conflicts identified? U Yes U No Describe conflicts: U Review homeowner preferences: Can aesthetics reconcile with site and building constraints? L Yes U No How? U Confirm type and condition of existing framing: U member sizes_ spans L connections U supports Q Confirm type and condition of foundation: U type U depth U size I3 Confirm types and condition of existing construction materials: U roof _ floor U walls U foundation !J Confirm soil information: U type U depth of rock Q bearing capacity U susceptibility to scour and erosion U Confirm characteristics of flood-related hazards: LI BFE U velocity U frequency Q duration U potential for debris flow_ O Confirm characteristics of non-flood-related hazards: • wind Useismic U snow U other: U Review accessibility considerations: • access/egress U special resources for elderly, disabled, children Architectural constraints noted: Is clearance available to install lifting beams andjacking equipment? U Yes U No U Check local codes/covenants for height or appearance restrictions: U deed/subdivision rules U local building codes Restrictions: Figure VI-E.25: Elevation Field Investigation Worksheet Structures VI -E.33 atrAfittinm Fiono.Prnne Resideantial *..M ,Q January195l l u Gu rIauwwo WI Is% .... to . IV-I-e o January 1995 ChapterVI: General Design Practices * Elevation DESIGN To illustrate the design process, a worked example is shown following the instructionsfor Steps1-7. in the Chapter VI section on Wet Floodproofing. The designer should refer to local codes for guidance on Steps 8 and 10. If building and flood guidance is not covered by the local building code, refer to ASCE 7. The design process for an elevated structure shown in Figure VI-E24 consists of the following steps: Step 1: Calculate gravity loads. The computation of gravity (vertical) loads such as building dead and live loads and buoyancy forces was presented in Chapter IV. Snow Loads: There are no "typical" formulas for houses, since the calculation of snow loads depends upon the building code in use, the geographic area in which the house is located, and the size and shape of the house and roof. The governing building codewill clearly spell out the correct procedure to follow. Most procedures are simple and straightforward. Some houses will be more complex due to their shape or quantity of snow that must be allowed for. However, the general procedure is as follows: * To determine the ground snow load, consult snow maps within the building code, and/or local requirements with the local building official. * Determine importance factors. * To determine the exposure factors, analyzethe surrounding terrain, trends in snow patterns, and slope of roof. * Determine the snow load. o Determineconsiderations for drifting snow by examining any adjacent house or structure, a mountain above the house, or higher roofs. VI -E.34 EnoineerinaPrinciplesand Practices of…a,1RPtrnfittinn FInnr.Prnna DaoLanflnr O+r…IL January 1995 Design * Determine considerations for sliding snow by examining steep slope on roof or higher roofs. Step 2: Calculation of lateral loads. The calculation of building lateral loads includes wind, seismic, and flood-related loads. One objective of the wind If the local building code does not and seismic analysisis to determine which loading condition cover wind, snow, or seismic issues, refer to ASCE 7. controls the design of specific structural components. Wind Analysis: There are no "typical" formulas for houses, sincethe calculation of wind loads depends upon the building code in use and the size and shape of the house. The governing building code will clearly spell out the correct procedure to follow. Most procedures are simple and straightforward. Some houses will be more complex due to their shape. However, the general procedure, as illustrated in Chapter IV, is presented below. * Determine wind speed and pressure by consulting wind maps within the building code, and checking local requirementswith the local building official. * Determine the importance factors and the exposure category. * Determine wind gust and exposure factors and analyze the building height and shape, whether the wind is parallel or perpendicular to the roof ridge, and whether it is windward or leeward of roofs/walls. * Determine the wind load. * Distribute the load to resisting elements based upon the stiffness of shear walls, bracing, and frames. Pnnineerinn Print-inipq and Practices of Retrofittina Flood-Prone Residential Structures VI-E.35 January 1995 Chapter VI: General Design Practices Elevation Seismic Analysis: There areno "typical" formulas for houses since the calculation of seismic loads depends upon the building code in use and the size and shape of the house. The governing building code will clearly spell out the correct procedure to follow. Some houses will be more complex due to their shape. However, the general procedure, as illustrated in Chapter IV, is presented below. * Calculate dead loads by floor. These include permanent dead loads (roof, floor, walls, and building materials) and permanent fixtures (cabinets, mechanical/electrical fixtures, stairs, new locations for utilities, etc.). * Determine if the snow loadmust be included in the dead load analysis. Most building codes require the snow load to be included for heavy snow regions. The building code will list these requirements. • Determine the seismic zone and importance factors. * Determine the fimdamental period of vibration (height of structure materials used in building). * Determine total seismic lateral force by analyzing site considerations, building weights, and the type of resisting system. • Distribute the loads vertically per the building code, keeping in mind additional force at the top of the building. * Distribute the loads horizontally according to the building code and the stiffness of resisting elements. The code-prescribedminimum torsion ofthe building (center of mass vs. center of rigidity), shear walls, bracing, and framesmust be considered. VI -E.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Flood-Related Forces: The computation of flood-related forces was presented in Chapter IV, and includes the following: * Determine Flood Protection Elevation (FPE). * Determine type of force (hydrostatic or hydrodynamic). * Determinethe susceptibility to impacts from debris (ice, rocks, trees, etc.). * Determine susceptibility to scour. * Determineapplicability of and susceptibilityto alluvial fans. * Determine design forces. * Distribute forces to resisting elements based upon stiffness. Step 3: Check ability of existing structure to withstand additional loading. Chapter IV presented general information on determining the ability of the existing structure to withstand the addi tional loadings imposed by retrofitting methods. The process detailed below is similar for each of the building types we expect to encounter. First, the expected loadings are tabulated and compared against allowable amounts determined from soil conditions, local code standards, or building material standards. The following list of existing building components and connections should be checked. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.37 January 1995 Chapter VI: General Design Practices Elevation Roofs: The plywood roof diaphragm, trusses, connections, and uplift on roof sheathing should be capable of resisting the increased wind and seismic loads. The American Plywood Association has published several references that are useful in this calculation. These include: * Roof Sheathing Fastening Schedules for Wind Uplift; * Diaphragms;and * Residential and Commercial These reference materials or the local building codes will give the designer the necessary plywood thicknesses and connection specifications to resist the expected loadings, and/or will provide loading ratings for specific material types and sizes. If the roof diaphragm and sheathing are not sufficient to resist the increased loading, the design can strengthen these components through the following: e increase the thickness of the materials, and/or * strengthen the connections with additional plates and additional fasteners. Roof Truss to Wall Connections: The roof trusses and truss connections to walls should be checked to ensure that they will resist the increased wind loads. Of critical impor tance are the gable ends, where many wind failures occur. The American Plywood Association has published several references that are useful in this calculation. These include: * Panel Handbook and Grade Glossary, and * Residential and Commercial. VI -E.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 For additional information on the performance of various building system products, refer to product evaluation reports prepared by the model code groups. Design These reference materials or the local building codes will give the designer the necessary truss size, configuration, and connection specifications to resist the expected loadings, and/or will provide loading ratings for specific truss and connection types and sizes. If the roof trusses and wall connections are not sufficient to resist the increased loading, the design can strengthen these components through the following: * increase the amount of bracing between the trusses; and/ or * strengthen the connections with additional plates and additional fasteners. Upper Level Walls: The upper level walls are subject to increased wind pressure and increased shear due to increased roof loads. Both the short and long walls should be checked against the shear, torsion, tension, and deflection, utilizing the governing loading condition (wind or seismic). The American Plywood Associationhas published several references that are useful in this calculation. These include: * PanelHandbookand Grade Glossary; * Residential and Commercial; and • Diaphragms. These reference materials or the local building codes will give the designer the necessary wall size and configuration and connection specifications to resist the expected load ings, and/or will provide loading ratings for specific wall types, sizes, and connection schemes. Fnnineprinn Princinles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.39 January 1995 Chapter VI: General Design Practices Elevation If the upper-level walls are determined to be unable to withstand the increased loadings, the designer is faced with the difficult task of strengthening what amounts to the entire house. In some situations this may be cost prohibitive, and the homeowner should look for another retrofitting method, such as relocation. Measures the designer could utilize to strengthen the upper-level walls include: * adding steel strapping (cross bracing) to interior or exterior wall faces; * adding a new wall adjacent to the exterior or interior of the existing wall; * bolstering the interior walls in a similar fashion; and/or * increasing the number and sizes of connections. Floor Diaphragm: The floor diaphragm and connections are subject to increased loading due to flood, wind, and seismic forces. The existing floor diaphragm and connec tions should be checked to ensure that they can withstand the increased forces that might result from the elevation. The American Plywood Association has published several references that are useful in this calculation. These include: * Residential and Commercial and * Diaphragms. These reference materials or the local building codes will give the designer the necessary floor size and configuration and connection specifications to resist the expected load ings, and/or will provide loading ratings for specific floor types, sizes, and connection schemes. VI -E.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design If the floor diaphragm or connections are determined to be unable to withstand the increased loadings, the designer could strengthen these components by: * adding a new plywood layer on the bottom of the existing floor diaphragm; * increasing the number and size of bracing within the floor diaphragm; and * increasing the number and size of connections. Step 4: Analyzeexisting foundation. The existing foundation should be checked to determine its ability to withstand the increased gravity loads from the elevation, the increased lateral loads due to soil pressures from potential backfilling, and the increased overturning pressures due to seismic and wind loadings. The designer should tabulate all of the gravity loads (dead and live loads) plus the weight of the new foundation walls to determine a bearing pressure, which is then compared with the allowable bearing pressure of the soil at the site. Not including expected buoyancy forces in this computation will yield a conservative answer. If the existing footing is insufficient to withstand the additional loadings created by the elevated structure, the design of foundation supplementation should be undertaken. The foundation supplementation may be as straightforward as increasing the size of the footing and/or more substantial reinforcement. The designer may refer to the ACI manual for footing design, recent texts for walls and footing design, and applicable codes and standards. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.41 January 1995 Chapter VI: General Design Practices Elevation Step 5: Design the new foundation walls. -itl The design of a new foundation, whether it be a solid or For wet floodproofing ap plica- open foundation, is usually governed by the local building tions, where openings in founda- codes. These codes will have minimum requirements for tion walls are necessary, ]refer to foundation wall sizes and reinforcing schemes, including the section on Wet Floodj proofing seismic zone considerations. The designer should consult in this chapter. the appropriate code document tables for minimum requirements for vertical wall or open foundation reinforcement. For new slab applications where the lower level is allowed to flood and the slab is not subject to buoyancy pressures, the designer can utilize the Portland Cement Association documentConcrete Floors on Ground as a source of information to select appropriate thicknesses and reinforcing schemes based upon expected loadings. The slab loadings will vary based upon the overall foundation design and the use of the lower floor. Step 6: Design top-of-wall connections. Top-of-wall connections are critical to avoid pullout of the sole plate, floor diaphragm, and/or sill plate from the ma sonry foundation. A preliminary size and spacing of anchor bolts is assumed, and uplift, shear, and tension forces are computed and compared against the allowable loads for the selected bolts. Where necessary, adjustments are made to the size and spacing of the anchor bolts to keep the calcu lated forces below the allowable forces. It is usual to include a factor of safety of 1.3 to respond to flood, wind, and seismic forces. VI -E.42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Step 7: Design sill/sole plate connections. The existing sill/sole plate connections will be subject to increased lateral loads and increased uplift forces due to increased wind and buoyancy loading conditions. The sill/ sole plate is designed to span between the anchor bolts and resist bending and horizontal shear forces. The designer should refer to the appropriate wood design manual that provides recommended compression, bending, shear, and elasticity values for various sill/sole plate materials. Using these values, the designer checks the connection against the expected forces to ensure that the actual forces are less than the allowable stresses. If the sill/sole plate connection is insufficient to withstand expected loadings, the size of the sill/sole plate can be increased (or doubled), and/or the spacing of the anchor bolts can be reduced. Step 8: Design new access. The selection and design of new access to an elevated structure is done in accordance with local regulations governing these features. Special homeowner requirements- for aesthetics, handicapped accessibility, and/or special requirements for children and the elderly-can be incorporated using references previously discussed in Chapter III. Connection of the new access to the house should be designed in accordance with the local codes. The foundation for the access measure will either stand alone and be subject to its own lateral stability requirements or it will be an integral part of the new elevated structure. In either case, analysis of the structure to ensure adequate foundation strength and lateral stability should be completed in accordance with local codes. It should be noted that any access below the BFE should incorporate the use of flood-resistant materials. The designer should refer to FEMA Technical Bulletin 2-93, Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.43 January 1995 Chapter VI: General Design Practices Elevation entitledFlood Resistant Materials Requirements for BuildingsLocated in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. Step 9: Design utilities extensions. The field investigation will reveal the specific utility systems that will require relocation, extension, or modification. Where possible, utility systems should be relocated above the flood protection level. Local utility companies should be contacted about their specific requirements governing the extension of their utility service. In many instances, the local utility company will construct the extension for the homeowner. Critical issues in this extension process include: * handling of utilities encased in the existing slab or walls; * coordination of disconnection and reconnection; * any local codes that require upgrades to the utility systems as part of new construction or substantial repair or improvement; * introduction of flexible connections on gas, water, sewer, and oil lines to minimize potential for seismic damage; * potential for relocation or elevation of electrical system components from existing crawl space and/or basement areas; and * design of separate GFI-type electrical circuits and use of flood-resistant materials in areas below the BFE. VI -E.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Step 10: Specify increased insulation requirements. Elevated floors and extended utility system components may increase the potential for heat loss through increased exposure and airflow and necessitate additional insulation. The designer should evaluate the energy efficiency of each aspect of the project, compare existing insulation (R-values) against the local building code, and specify additional insulation (greater R-value) where required. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.45 January 1995 d -V Chapter VI:General Design Practices Elevation Elevation Sample Calculation GIVEN OR OBTAINED FROM THE FIELD INVESTIGATION: The owner ofa single-story crawlspace home intends to elevate the structure to eliminate a repetitive flooding hazard. Her desire is to raise the structure one full story (8 feet) and use the lower level for storage and parking. She contracted with a local engineer to perform the design. The engineer's investigation revealed the following information about the existing structure: * crawlspace home with four (4) block courses (no reinforcement); * the first-floor elevation is two (2) feet above the surrounding grade (which is level); * the property is located in a FEMA-designated floodplain (Zone A4) and is subject to a 100-year flood four (4) feet in depth above ground level; * floodwater velocities in the area of the house average six (6) feet per second; * floodwater debris hazard exists and is characterized as normal; and * the structure is classified as apre-FIRM structure. FIRSTFLOORt*e-eOI LO EXISTING FRONT ELEVATION 1 of 44 VI -E.46 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures January 1995 Elevation Sample Calculation Elevation Sample Calculation Additional Information on Existing Home * Wood-Framed House 30 ft. x 60 ft. * Gable Roof 4:12 slope * Per the 1991 Uniform Building Code -80mph WindZone -SeismicZone2B -Ground SnowLoad of 40 psf * Flat open terrain surrounding house -IIIrII_ T . . T-I 1. . . . . .r. . . .nr'l|TI ...... _;_-VENT r, r Fb . .T1....rPROPOSED SIDEELEVATION pf~r?~-c ~~~~ 0 ~~~~~~~~~8 16 ~ ' ... . ' A .' .............. :.: A ~.. ~~~!... ......... Extended foundation walls are proposed to be constructed of 8-inch-thick concrete masonry units. The existing footing is 2 feet wide by 1 foot thick concrete reinforced with 3-#4 rebars continuous and#4 dowels extending up into masonry 24 inches. Slab on grade will be 3-1/2 to 4 inches thick. Interior walls ofthe living area (elevated) are composed of 4-inch studs at 16 inches o.c. with plaster on each side. Exterior walls have 4-inch studs at 16 inches o.c., plaster on the inside, and sheathing and wood siding on the exterior-walls are insulated with fiberglass insulation. 2 of 44 Ennineerinn Print-inhs and Practicesqof Retrnfittinn Flood-Prone ResidentialStructures VI -E.47 J-ay--._ WI _1_ _.M995_- __ January 1995 Chapter VI: General Design Practices Elevation _ Elevation Sample Calculation First-floor fiaming consists of2xl 2's at 16 inches on center supported by the exterior long walls and a center support. Floorcoverings are hardwood (oak) with a 3/4-inch plywood subfloor. There is 10 inches of insulation betweenthejoists. A gypsum ceilinginthe proposed lower area is planned. ,:e,:::'.:,: ~ ~ ~ :.'.N~ ~ ~ ~ .. .... .:. N .,:' -F N Roof fiwning consists of pre-engineered wood trusses at 16 -iches on center. Thetop chord consists of 2x6's and the web andbottom chordconsist of 2x4's. The roof is fiberglass shingles withfelt on 1/2-inch plywood. Theceiling is 1/2-inch plasterwith 1/2-inchplywood backup. There are 16 inches of fiberglass insulation above the ceiling. : : : L 11.1:,::;:.:: LIA L : -U..., T, : :I II II~~~ ~~IfI ~~ r~ I Ifiit1 A: WA i, r1VI>1:l5. 11 111!11t :llI~I1 .~:....... :: . : 2 ~ ilVC)1lS~ W M96 91 -- ............... 14"WRA. AMINS: PLAN: ... ....... 3 of 44 VI -E.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 1: Calculate Vertical Loads fI Elevation Sample Calculation Calculations: Step 1: Calculate vertical flood loads The calculation of buoyancy forces and comparison with structure weight is a critical determination of this problem. While buoyancy ofthe first floor is not an issue (since it is elevated four feet above the BFE), buoyancy ofthe entire structure (slab, foundation walls, and superstructure) must be checked if dry floodproofing is being considered for the lower level. If buoyancy forces control, dry floodproofing ofthe lower level is not applicable. Calculate Buoyancy Forces (from Formula IV-8) Fb = yAH = (62.4 lbs/ft3)(30ft x 60 ft)(4 ft) = 449,280 lbs Calculate StructureWeight by Level Tabulate Dead Loads by Floor Roof: Shingles -Asphalt -1layer 2.0 psf Felt 0.7 psf Plywood-32/16 -1/2 inch 1.5 psf Trusses @ 16 inches o.c. 5.0 psf 2x6 Top Chord 2x4 Web and Bottom Total 9.2 Vsf (RQof) 4 of 44 Ennineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.49 January 1995 Chapter VI: General Design Practices Elevation , E Elevation Sample Calculation First Floor Ceiling: Insulation-16inch of fiberglass 1/2inchlplywood 1/2inch plaster and lath Misc., heating, electrical, cabinets 8.0 psf 1.5 psf 10.0 psf 2.0 psf Total 21.5 psf (1st Floor Ceiling) FirstFloor: Oak Floor Subfloor-3/4 inch plywood Joists (2x12) Insulation -10 inch fiberglass Misc., piping, electrical Gypsum ceiling -1/2 inch 4.0 psf 3.0 psf 4.0 psf 5.0 psf 3.0 psf 2.5 psf Total 21.5psf (lst Floor) Wails: Interior -wood stud, plaster eachside Exterior -2x4 @16 inches o.c., plaster insulation, wood siding Lower Level -8 inch masonry, reinforcement at 48 inches on center 20 psf 18 psf 50psf 5 of 44 VI -E.50 Enaineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 1: Calculate Vertical Loads Elevation Sample Calculation Total Weights by Level Roof: Surface Area = [15.81 ft. + 2 ft. overhang]x[60 ft + 2 ft. overhang]x[2] = 2208 ft2 Projected Area = [15 + 2 (15/15.81)]x[60 + 2]x[2] = 2095 ft2 Shingles: 2208 ft2(2 psf) = 4416 lbs Felt: 2208 ft2 (0.7 psf) = 1546 lbs Plywood: 2208 ft2(1.5 psf) = 3312 lbs Truss: 2095 ft2(5 psf) = 10,475 lbs First Floor Ceiling: Area=60x30= 1800 ft2 Insulation: 1800 ft2(8 psf) = 14,400 lbs Plywood 1800 ft2(1.5 psf) = 2,700 lbs Plaster 1800 ft2(10 psf) = 18,000 lbs Misc. 1800 ft2(2 psf) = 3,600 lbs Walls 1801fext. (4' trib.)( 8 psf) = 12,960 lbs 157 Ifint. (4' trib.)(20 psf) = 12,560 lbs Subtotal W2 = 83,970 lbs 6 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.51 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation First Floor Including Lower Level: Area = 60 x 30 = 1800 ft2 Oak Floor 1800 ft2(4 psf) = 7,200 lbs Subfloor 1800 ft2(3 psf) = 5,400 lbs Joists 1 800 ft2(4 psO = 7,200 lbs Insulation 1800 ft2(5 psO = 9,000 lbs Misc 1800 ft2(3 psf) = 5,400 lbs Ceding 1800 ft2(2.5 psf) = 4,500 lbs Walls 180 If ext. (4' trib.)(18psf) = 12,960 lbs 157 Ifit. (4' trib.)(20 psf) = 12,560 lbs 285 If lower level (4' trib.)(50psf) = 57,000 lbs Subtotal W1 = 121,220 lbs Total Weight, W = WI + W2 = 205,190 lbs = 205 kips CompareBuoyancyForce Against Structure Weight DL=> 1.5 Fb 205,190 lbs <= 1.5 (449,280) 205,190 lbs < 673,920 lbs Therefore, buoyancy forces control and the building (ifdry floodproofed) will float during flood events, unless structural measures, such as floor anchors or additional slab mass, or non- structural measures such as allowing the lower level to flood, are utilized to offset/equalize the buoyancy forces. In our example, since buoyancy controls and the magnitude ofthe project represents a substantial improvement, the homeowner is required to allow the lower level to flood by incorporating vent openings in the foundation wall. While this action will equalize hydrostatic pressures on the foundation walls, hydrodynanmic and impact forces will still apply. 7 of 44 VI -E.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation Step 2: Compute lateral loads Lateral Flood Loads Compute lateral hydrostatic forces due to four (4) feet of water moving at six (6) feet per second. FromFormulaIV Fh 1/2 yH1 = (1/2) (62.4 lbs/ft3 ) (4 ft)2 = 499.2 lbs/lf acting at 1.33' FromFormulaIV-9 CdV2 (1.25) (6 ft / sec)2 dh = 2g = 2 (32.2 ft/sec2) = 0.70 ft FromFormulaIV-10 Fdh = y (dh)H = (62.4 lbs/ft3 ) (0.70 ft) (4 ft) = 174.7 lbs/lf acting at 1.33' FromFormulaIV-11 F FH+ FH = h +dh = 499.2 lbs/lf + 174.7lbs/lf = 674 lbs/lf acting at 1.33' Because the owner decided to intentionally flood the lower level, the above-calculated lateral hydrostatic flood forces are negated and not considered further in this example computation. However, if dry floodproofing were being considered, these lateral forces may have exceeded the allowable stress on the wall, resulting in a probable wall failure. 8 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.53 January 1995 Chapter VI. General Design Practices Elevation Elevation Sample Calculation Calculate Hydrodynamic Forces on CMU Wall (From Formula IV- 12) V2 = (1.25) (1.94 slugs/fl3 ) [6 ft lseC)2 = 43.65 lbs/ft2 bh = 3 ft = 7.5 < 12 4 ft Table IV-3 Cd = 1.25 Calculate Total Force on Building Face (upstream) (From Formula IV-13) Fd PdA = (43.65 lbs/ft2) (4') (30') = 5,238 lbs From geotechnical conditions, a friction factor of 0.3 may be used. Dead load of structure = 839 lbs/ft (180 fl) = 151,020 lbs Calculateresistancedue to foundationfriction Rf = 151,020 lbs (0.3) = 45,306lbs Since 45,306 lbs> 5,238 lbs., building will not slide. 9 of 44 VI -E.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation SampleCalculation Calculate Normal Impact Forces (FromFormulaIV-14) F -wV n gt (1,000 lbs) (6 ft l sec) 186lbs (32.2 ft/sec 2 ) (1 sec) Since vents are being used to equalize the hydrostatic pressure, the wall will be subject to a net load equal to the combined hydrodynamic and impact loads. The ability of the new foundation wall to withstand these forces is presented toward the end of Step 5. WIND Since the house is being elevated, wind pressures will be increased on the home. Depending upon the amount of elevation, additional bracing of the roof or walls may be necessary. Reference: 1991 Uniform Building Code Basic wind speedhasbeendeterminedtobe 80mph. (From Figure 23-1 in 1991 UBC and verification with local building official.) From Table 23-F, wind stagnation pressure (q) based upon wind speed is: q5= 16.4 psf From Table 23-K, Building Category is IV From Table 23-L Importance factor for wind, I = 1.0 From Definitions, Section 2312, House is Exposure C From Table 23-G, Combined Height, Exposure and Gust Factor Coefficient (Ce)is Height Above Ground Ce 0-15 ft 1.06 20 1.13 25 1.19 10 of 44 ResidentialStructures VI -E.55 nr-aineerinn Prinninles and Practices of Retrofitting Flood-Prone January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation From Section 2316, Equation 16.1 P CeCqsj where, P = Design WindPressure C = Combined Height, Exposure and Gust Factor Ce = Pressure Coefficient for Structure or Portion q = Wind StagnationPressure I = Importance Factor for this house, P = (1.06)(Cq)(16.4psf)(1.0) = 17.4(Cq)psf (L113) (Cq)(1 6.4 psf)(. .0) = 18.5(Cq)Psf (1I.1 9)(C )( 16.4 psf)( 1.0) = 19.5(Cq)Psf where Cq is determined from Table 23-H. Primary Frames and Systems Using Method 1 outlined in 1991 UBC Note: Elements and Components of the Building should be checked. (i.e.,siding, shingles, gable ends, windows, etc.) 11 of 44 VI -E.56 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation From Table 23-H, pressure coefficients are Walls: WindwardWall LeewardWall Cq= 0.8 Cq = 0.5 ib C award outward Roof: Wind perpendicular to ridLeeward Roof Windward Roof 4:12 slope ge: C = 0.7 Cq = 0.8 Cq =0.3 outward outward or inward Wind parallel to ridge: Cq =0.7 outward 12 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.57 January 1995 Chapter VI: General Design Practices Elevation jI Elevation Sample Calculation I Wind.Perpendicular to Ridge Walls: Windward: (inward) P = 17.4psf (0.8) = 14.0psf (0-15 R) P= 18.5psf (0.8) = 14.8psf (20 It) Leeward: (outward) P = 17.4 psf (0.5) = 8.7psf (0-15 ft) P = 18.5psf (0.5) = 9.3psf (20 It) Roof: Windward: (outward) P = 18.5 psf (0.9) = 16.7 psf (20 ft) or (inward) P = 18.5psf (0.3) = 5.6 psf (20 ft) 0 Leeward: (outward) P = 18.5psf (0.7) = 13.0 psf (20 ft) RIME 13 of 44 VI -E.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation Wind Parallel to Ridge Walls: 'imdward: (inward) Leeward: (outward) P = 19.5 psf (0.8) P = 19.5 psf (0.5) = 15.6 psf = 9.8 psf (25 ft) (25 ft) Roof: P = 18.5 psf (0.7) P = 19.5 psf (0.7) = 13.0 psf (20ft) = 13.7 psf (25 ft) Seismic Since the house is being elevated, the potential for seismic loading/overturning design loads will be increased on the home. Depending upon the amount of elevation, additional bracing of the roof or walls may be necessary. Reference: 1991 Uniform Building Code Seismic Zone 2B has been determined for this home (Figure 23-2 in 1991 UBC and verification with local building official). 14 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.59 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation The seismic load on the house depends upon the dead load. This load must be tabulated on a floor-by-floor basis as was presented in Step 1 under Tabulate Dead Loads by Floor. Check if Snow Load must be included in Seismic calculations: Reference: 1991 Uniform Building Code Ground Snow= 40 psf Roof Slope, a= 18.40 From Table A-23-T, Importance factor, I = 1.0 From Table A-23-S, Snow Importance factor, CI 0.6 From Section 2343, Equation 434lA Pf = C01P where, Pf = MinimumRoofSnowLoad ICe = Snow Exposure Factor I = Importance Factor P8 = Basic Ground SnowLoad 9~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ for this house, Pf= 0.6 (1.0) (40 psf) =24 psf< 30 psf thus, by Section 2334(a)3 snow load is not included (it is recommended that the building official be consulted if in doubt) and the total weight of 205 kips as calculated in Step 1 under Tital Weighak by Level can be used in this seismic analysis. 15 of 44 VI -E.60 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation From Section 2333(h)2D, Table 23-0 and Table 23-J the Static Force Procedure may be used. hi= 10'-0", heightto First Floor h2 = 10'-0"+ 8'-0"= 18'-0" heighttoFirstFloorCeiling per UBC Section 2334(b)2A, equation 34-3 the fundamental period of vibration, in seconds, T T = C(hn)3/4 where, T = Fundamental Period of Vibration, in seconds Ct Numerical Coefficient hn = Height at Level n, in feet Leveln UppermostLevel for this house, C, =0.02 h 18'-0" therefore, T = 0.02 (18.0)3/4 = 0.175 seconds From our field investigation (and NRCS soil reports), it was determined that the soil profile was dense (S2) to a depth of over 200 feet. Thus per Table 23-J the site coefficient for S2is S = 1.2 16 of 44 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.61 January 1995 Chapter VI: General Design Practices Elevation f Elevation Sample Calculation Per UBC Section 2334(b), Equation 34-2 C = 1.25 S/T213 where: C = Numerical Coefficient S = Site Coefficient T = Period of Structure for this house, 1.25 (1.2) C=(0.17)23 = 4.79 > 2.75 maximum by code, therefore use C = 2.75 From Table 23-I, Seismic Zone Factor, Z = 0.20 From Table 23-L, Importance Factor, I = 1.0 From Table 23-0, Section 2333(0 and Section 2334(c), Numerical Coefficient, Rw = 6 Per UBC Section 2334(b), Equation 34-1, the total seismic design lateral force is, V = ZICW/Rx where: V Total Seismic Lateral Force I = Importance Factor C = Numerical Coefficient R = Numerical Coefficient w W = Total Seismic Weight thus for this house, V = 0.2(1.0)(2.75)(205 kips)/6 = 18.8 kips Per UBC Section 2334(d) & (e) the total lateral force due to seismic must be distributed vertical and horizontally. 17 of44 VI -E.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation First consider load acting perpendicular to long direction of house. .S.. i~....i-. ,~~~~~~~..=.: -..,'-:, -. .--., ..'..-"'''-' LEVELI-- 0 . ...... '.''.'"'........., -: .. ...... .. 5i-... ....-... ii EE -N N.V:i .... UE~l Per formula 34-7 the "extra" force at the uppermost level is Ft = 0-07 TV where: F. = "Extra"Force T = XPeriod V = Total Seismic Lateral Force for this house T < 0.7 seconds, therefore the building code allows us to set Ft 0.0 the forces are distributed vertically by formula 34-8, (V -Ft)w~hx where: V = Total Seismic Lateral Force F -"Extra" Force at Top W -Weight of Level Under Consideration hx= Height to Level Under Consideration 18 of 44 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -E.63 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation for this house, LATERAL FORCES PERPENDICULAR TO LONG DISTANCE Seismic Level First Floor Ceiling 1 Height (ft) hxWX 10'-0" 18'-0" Level Weight (kips) 83.97 121.22 (wx)(h)x 840 2182 Lateral Force (kips) Fx 5.23 13.57 Level Shear (kips) FX 5.23 18.8 3022 18.8 Wind Level Wind Pressure (psf)( V Px Area f ax Lateral Force (kips) HxIFx Level Shear (kips) First Floor Ceiling 11.12 11.12 1 (14.0+8.7) (8')(60') 10.9 22.1 19 of 44 VI -E.64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 2: Compute Lateral Loads Elevation Sample Calculation F. (18.8--O0)w h 0 h, =o.006221w 3022 * Wind Pressure Calculations for First Floor Ceiling (Load = Area x Pressure) worst shear is generated by 5.6 psf inward or windward Roof: (pressure) (area) (slope) (5.6+13.0psf) (15.81ft) (60ft) (5/15.81) =5.58kips Wall: (area) (pressure) (1 ft) (60 ft) (14.87 + 9.3 psf) = 1.45 kips a (3 ft) (60 ft) (14.00 + 8.7 psf) 4.09 kips . 11.12kips LATERAL FORCES PARALLEL TO LONG DIRECTION Seismic Level Lateral Level Height Weight Force Shear (ft) (kips) (kips) (kips) Level hx -WX (w)(h) Fx IFX First Floor Ceiling 10'-0" 83.97 840 5.23 5.23 1 18'-0" 121.22 2182 13.57 18.8 3022 18.8 20 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.65 January 1995 Chapter VI: General Design Practices Elevation Eev S Elevation Sample CalculationI Wind Wind Lateral Level Pressure Area Force Shear (ps) (ft2) (kips) (kips) Level PX ax HX Fx First Floor Ceiling * * 4.57 4.57 1 (14.0+8.7) (8')(30') 5.45 10.02 * Wind Pressure Calculation for First Floor Ceiling (Load = Pressure x Area) Gable: (area) (pressure) 1/2 (1)(12/(4)( 1')(1 5.6 + 9.8 psf) =0.04kips <* [l/2(30)(5)-1/2 (1)(12/(4)(1)](14.8 + 9.3 psf) = 1.77 kips v* Wall: (area) (pressure) (30 fi) (1 ft) (14.87 + 9.3 psf) =0.72kips* (30 ft) (1 ft) (14.0 + 8.7 psf) =2.04kips 4.57 kips From the previous two tables it is seen that: a Wind controls when forces are in the perpendicular to the long direction (both floors). * Seismic controls when forces are in the parallel to the long direction (both floors). 21 of 44 VI -E.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 3: Check Existing Structure for New Loads Elevation Sample Calculation Step 3: Check existing structure for new loads For this example analysis, the existing structural components were assumed to be adequate for the loading conditions. However, the designer should check the existing truss-to-wall-connec tions, plywood roof diaphragm, upper level walls, and floor diaphragm for their ability to resist increased loadings. Step 4: CheckExistingFoundation Per UBC Table 23-A, LiveLoad = 40 psf with no concentrated loadrequirementsfor a 1 foot-wide strip through the short distance ofthe house Snow: (24 psf) (1') (1 5'+2' overhang) = 408 plf First Floor LL: (40 psf) (1') (15'/2) = 300plf Dead Loads: Roof: shingles: (15.81' +2') (2 psf) (')= 35.6plf felt: (15.81' + 2') (0.7 psf) (1') = 12.5 plf plywood: (15.81' + 2') (1.5 psf) (1') 26.7plf truss: (15' + 2'(15/15.81)) (5 psf) (1') = 84.5 plf Ceiling: insulation: (1 5') (1') (8 psf) = 120 plf plywood: (15') (1') (1.5 psf) = 22.5 plf plaster: (15') (1') (2Opsf)= 150plf misc: (15') (1') (2 psf) = 30 plf wall (ext) (4') (1') (18 psf) = 72 plf wall(int)' (15'/2) (1') (20 psf) 150plf First Floor: flooring: (15'/2) (1') (4 psf) = 30plf subfloor: (15'/2) (1') (3 psf) = 22.5plf joists: (15'/2)(1') (4 psf) = 30 plf insulation: (15'/2) (1') (5 psf) = 37.5 plf misc: (15'/2) (1') (3 psf) = 22.5 plf ce:ing (15'/2) (1') (2.5 psf)= 18.8plf wall (ext) (4') (1') (18 psf) = 72plf 22 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.67 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation wall(int~l (15'12) (1P) (20 psf)= 150plf new lower level wanl (lO') (11)(50 psf) = 500Ipf Total Dead Load 1587 plf ' Note that a 20 psfpartition load is applied here; this approach is conservative due to the amount of interior walls in this building. From our field investigation it was determined that an allowable bearing pressure of 2000 psf was acceptable. Total gravity load on foundation: Snow + Foundation it = + Live + Dead + Soil = 408 plf+ 300 plf+ 1587plf+ 2'(1')(150pcf) + [(24"-8")/ 12](29)(120pcf) -2915plf = The existing foundation is 2'-0" wide, thus the bearing pressure for gravity loads is BP = 2915plf/ 2 ft = 1458 psf < 2000 psf allowable Existing Foundation is Acceptable. (Note: This is a worst case scenario by assuming no buoyancy effects.) Step 5: Designof NewFoundation Wall Using UBC minimum requirement for masonry walls in Seismic Zone 2B, From Table A-24-3-B minimum vertical wall reinforcement for 80 mph wind, Exposure C, 2 story (first story of 2-story building) unsupported height of 8'-0" minimum= #3 rebars @ 72" o.c. 23 of 44 VI -E.68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Januarv 1995 Elevation Sample Calculation Step 5: Design of New Foundation Wall Elevation Sample Calculation However, since the house is in seismic zone 2B, Section 2407(h)3 ofUBC applies for minimum reinforcement. See typical Hollow -Masonry Unit Exterior Foundation Wall Detail. t ;;; i; ..... .--.-.' t. K!'.':.i.:'0 .. .. . ;..i. : : . i i. -. ;, :';;t t. . :. ... 0.' i L .... '."E 'E. ,g,,, :., -.,::.,:: E -,.. , ... :i. -.. ':..-::".... '.E:::i2<:'<-:fi::::gs4xe.A .......... .::.: -........ ~~~~~~~~~~~~~~~.i .:-E. ?: ............ .. ....... .... :.:.:.: ,. ". t: ' .,. ' ', ':EC.BX,. , .,::S. ', ......................... . . . . . . . .. . . . . . . . . . . .,:: " ~ ~ ~ ~ ~ R .. ... --.. .............. i.-X-.-;..,1''ii ".'':.i'~-~:''.-HL.oW.Y,'l.... ''' ~ ~~~~~N .,,: ............... .6.. M5R CHECK SHORT WALLS FOR LATERAL LOADS (SHEAR WALL), TENSION AND TORSION BIWBE Wind shear per wall = 22.1kips /21=1.05 kips per wall ~~E I Total seismic shear 18.8 kips UBC Section 2334(e) requires a 5% x building length induced torsion on seismic loads. For this house the center of mass and the center of rigidity will coincide. 5%(60'-0")= 3 ft. of induced torsion therefre, 18.8kips x 3 ft = 56.4 k-ft This results in shear in one wall being increased; thus, the total seismic shear for short wall is 18.8kips/2 + 56.4 k -ft/60 ft = 10.3 kips per wall Therefore,windcontrolsforshortwalls. 24 of 44 Encineerinc Prinninles and Practices of Retrofitting Flood-Prone ResidentialStructures VI -E.69 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation Worst Case, wall with penetrations. ,NECEO0EC7 I ~-CN MCORSE He .11 11- S = DRPY-I B/ NEAW LINTEL II i I II I 2: II i i WALI A. ff-i tZ INER1A. r164 1 AREA I |2 .3 . 1 Z2 s 23:2 SAMPLE ELEVATION 4 Assume #4 reinforcing bars @ 48" o.c in solid grouted cores. The total load of 1 1.05 kips must now be distributed to the wall according to stiffness of the elements ofthe wall. (height/length),= 101 /20' = 0.5 (height/length), = 10'/7 = 1.42 Since both height to length ratios are between 0.3 and 10, both shear and flexural deformation must be considered. With #4@48" o.c. the equivalent solid thickness is 4.6 inches= 0.38 ft. Reference: National Concrete Masonry AssociationNotes Assume shear modulus, G is 0.4 E where E = modulus of elasticity 25 of 44 VI. -E.70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 5: Design of New Foundation Wall Elevation Sample Calculation Assume compressive strength of masonry, f m = 2000 psi and type M or S mortar per ACI 530-92 Table 5.5.1.3, Em = 2.2 x 1 06 psi total deflection, U = Uf+ UV where: U = Total Deflection Uf= VH3/(12EI) Deflection due to Flexure UV= 3VH/(EA) Deflection due to Shear thus for this house, _ vl (H4l)3 3VjHj ul I + 12EmI EmAi V1H, 3 3V¾H 11111 U" 12EmI11 E.All Since the walls are interconnected by the floor diaphragm, the deflections for parts I and II will be equal. This calculation uses two equations, which give the load distribution into walls I and II. For more information on the use ofthese formulas, refer to a structural engineering text on shear walls. thus, Vl (H2 3VH1 _ VJH11 3 3VIIH1 1 .12EmI1 EmAi 12EmIi EmAII 26 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.71 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation vl1)3+ 3+{10) V,1(10)3 3V,1(10) 12(253) 7.6 12(10.9) 2.7 simplifying results in, 4.28VI -18.76VII= 0.0 by IF we get a second equation, VI +V =P= ll kips Solving the above two equations results in, VI 8.96kips=> 8.96 kips/20 ft = 0.45 kips/ft. V 1= 2.04 kips=>2.04 kips/7 ft = 0.29 kips/ft. Area V1 controls for bolt shear and wall shear. From UBC Section 2406(c)7B, M 8.96 kips(10') = 2 ~~=0.75 <1.0 Vd 8.96 kips(-)(20') 3 thus, allowable shear stress is (by equation 6-10 from UBC) Fv = 3(4-Vd ) < 80-45 M thus, F, = (1/3)(4-0.75)(2000)112 = 48.4 psi > 46.25 psi Since we will not be specifying "special inspection," UBC 2406(c) states that allowable stresses must be reduced by 1/2. 27 of 44 VI -E.72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation [Elevation Sample Calculation Thus, Fv = 46.25/2 = 23.1 psi the applied stress, f is V fv = V/(bjd) where: b = Width of Section j = Ratio of Distance between Centroid of Flexural Compressive Forces and Tensile Forces, d d Distance from Extreme Compression Fiber to Centroid of Tensile Reinforcement If we neglect the small axial forces in this wall, and assume equal distribution of reinforcement d 20'/2 + (2/3)(20'/2) = 16.67 ft. j = (2/3)(20')/16.67' = 0.8 forface shell bedding of masonry, width of sectionresisting shear is limited to mortarjoints; thus, b = 2 (1.25") = 2.5" thus, f =[8.96/((2.5)(0.8)(1 6.67)(12))]- 1000=22.4 psi since f < F wall is O.K. for shear. Use face shell bedding, no special inspections required. Does wall go into tension? 28 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.73 January 1995 Chapter VI:General Design Practices Elevation Elevation Sample Calculation maximum flexural uplift = VH/[(2/3)(20')] = 8.96 (10')/13.3 =6.74 kips stress block is triangular in shape, thus maximum stress is at end of wall, 6.74 kips = (l/2)(10') Pma Pmax=1.35 kips = 1350 lbs t gravity loads, selfweight: 10'(50 psO = 500 lbs 4 wallabove:8'(18psf) = 144Albs 644 lbs . thus the net tensile force = 1350 lbs -644 lbs = 706 lbs consider distributed over 1 foot length b = 2.5'1 thus ft= 706/(2.5"1 (12") = 24 psi > Ft = 2512 = 12.5 psi (per UBC 2406(c)4) However, since stress is very low, by observation we can say that the minimum reinforcement will take the slight tensile load. WIND PERPENDICULAR TO SHORT WALL UNDER CONSIDERATION (CHECKING VERTICAL SPAN FROM SLAB TO FLOOR) P = (8') 14.0 psf)/2 = 56 lbs/ft. M = wl2/8 = (14)(8)2/8 = 112 lb-ft/ft = 1344 lb-in/ft Check wall for assumed minimum reinforcement (#4 @ 48" o.c.), assuming T-section assembly. 290f44 VI -E.74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 5: Design of New Foundation Wall Elevation Sample Calculation per ACI 530-92 Section 7.3.2 1-4 (A .. 4-2 S j-EMPTY CORES IN p1-L I wTn I II un a .. us _L ~~~CORE i X H \ I f V -a I _-L~~~~~~~T-SEA4M ET £WE 4-II I b.. WIND PERPENDICULAR TO WALL N T. S. I c-c bars = 48" be min 16 (wall thickness) = 48" 1 72" d = 75/8 12 = 3.81 in. by the use of working stress design, (T-Beam analysis) it is determined that maximum compressive stress, f0 = 35 psi maximum tensile stress, f = 1890 psi Per UBC 2406(d)A, maximum allowable tensile stress in reinforcement is Fs =0.5 (fy) < 24,000 psi = 0.5(60,000) = 30,000 > 24,000 .-. use F. = 24,000 psi For no "special inspections" multiply by 1/2, thus F5 =12,000 psi >>> f = 1890 psi O.K. Per UBC 2406(a)3, maximum compressive stress Fb =0.33 f' = 0.33 (2000 psi) = 660 psi 30 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI- E.75 January 1 995 Chapter VI: General Design Practices Elevation Eevatio S Elevation Sample Calculation For no "special inspections" multiply by 1/2, thus Fb= 660 /2 = 330 psi >>> f O.K. Determine Ability of Wall to Withstand Hydrodynamic and Impact Forces Moment in wall is, 186 (8') 14 psf(8')f 43.65 psf(8')2 Qi + w11 + w212 = 16+ + 4 16 16 4 16 16 = 602.6 lb-ft Q 3wl W21 186 3(14 psf)(8') (43.65 psf)(8') + + + 2 8 8 2 8 8 = 178.7 lbs/ft w/impact = 85.7 lbs/ft w/o impact M =-+= Q w1l 3W21 186 14 (81) 3 (43.65 psf)(8') = -+ + = + + Pbot 2 8 8 2 8 8 = 238 lbs/ft w/impact = 145lbs/ft w/o impact Note: Forthe connection design for the top of wall to floor, impact need not be considered acting over the entire wall (that would assume a row of debris or logs hits the house at one time). kV 31 of 44 I VI E. 76 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1 995 Elevation Sample Calculation Step 5: Design of New Foundation Wall Elevation Sample Calculation For this load, try using #5 @ 48" O.C., assuming a T-section assembly. B =48" d =3.81" By the use of working stress design (T-beam analysis), it is determined that, MT = (602.6 lb-ft) (48" ) = 2,401.1 lb-ft maximum compressible stress, f'c = 548 psi maximum tensile stress, f = 26,253 psi S Note: f = 26,253 > F, = 24,000 psi allowable by UBC 2406(d)A; however, since an impact load is included in the loading under consideration, most building codes consider this a "short term" load and allow a 1/3 stress increase. Also note that with this amount of loading, it becomes feasible for "special inspections" of the masonry construction, and if the owner has qualified personnel to inspect the construction, the 1/2 allowable clause in the building codes no longer applies and the design can consider the full strength ofthe masonry. Thus, this design may be acceptable if the building code allows 1/3 stress increase and "special inspections" are performed. try #5 @ 24" O.C. b = 24" d =3.81 32 of 44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-E.77 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation 24" MT= 602.6lb-ft (--): 1,205lb-ft T ~~~12'1 maximum compressive stress, f 'c = 362 psi maximum tensile stress, f S = 13,354 psi This design is acceptable if 1/3 stress increase is allowed for impact however, the "special inspections" would not need to be perforned. The owner/engineer should decide which design is more cost effective. Also note that the above neglects axial load onthe masonry. This was done to simplify the calculations. In the wall, compressive stresses will be slightly higher and tensile stresses will be slightly lower. See ACI S30 for further information onthis subject. 8"CMIJ wall w/#5 @ 24" O.C.centeredon grouted cell -2,000 psi masonry (fPm)is acceptable. Step 6: Design top of wall connection. (Checking anchor bolts for pullout from masonry) Try 1/2"4A307 anchorbolts @ 4'-0" o.c., Wall I is worst case (see above) shear per b olt=0.45 k/ft. (4 ft.) 1.8 kips bolt It,~~~~~~~~~~~~~~~~~~~~~M upliftonbo P =5.56 (8)120=2.22 kips -ian; p= 2.22 (2) 15 =0.3 k/ft by ratio, thus, uplift on bolt = {(0.22+0.3)/2}(4')=1.04 kips/bolt try 1/2" 4 A307 anchor bolt, area of bolt, Ab = 0.2 in2 edge distance, Ibe=75/8 /2 -/2/2 = 3.56" embedment, lb = 4" (chosen) 33 of 44 j VI -E.78 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 6: Design Top of Wall Connection Elevation Sample Calculation Reference: ACI 530-92 Section 5.14 & UBC Section 2406(h) Ap = min (rlb2 or 7lIb 2) = 7I(3.56)2 3 9 .8 in2 allowable load in tension, 0.5(Ab)j Bt = mm 0.2(Ab)fy where: Ab = Area of Anchor Bolt film = Compressive Strength of Masonry f = Yield Strength of Anchor Bolt y for this anchor bolt pattern, Bt = min (((0.5)(39.8)(2000))¼4),(0.2)(20ksi)) 890,800 = 800 lbs < 1.04 kips by inspection the bolt will not work for combined shear and tension, Lower bolt spacing to 2'-O" o.c. pi =0.3 kips/ft by ratio, p2 =0.26 kips/ft uplift on bolt = {(0.3+0.26)/2}(2')= 0.56 kips < 800 lbs O.K. shear per bolt = 0.45 kips/ft (2') = 0.9 kips 34 of 44 EnningaarinnPrin,,infa and Pratirce nf Retrnfiffinn Flond-PronA ResidentialStructures VI -E.79 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation allowable load in shear, 350((f'm) Ab)"14 mnn0.2Abfy) where: AN = Areaof Anchor Bolt f'm = Compressive Strength ofMasonry f = Yield Strength of Anchor Bolt y for this anchor bolt pattern, Bv=min (350((2000)0.2)M),(0.12(0.2)(20ksi))= 1565,480 480 lbs < 0.9 kips If this pattern will not work, try upsizing bolts to 7 2 -0 oc, Ab =0.60 in2 Ap= it(751s/2 -7/8/2)2 = 35.78 in2 B.= min (0.5(35.78)(2000)'2),((0.2)(0.6) 20ksi) = 800,2400 = 800 lbs B= min (350((2000)(0.6)/),((0. 12)(0.6) 20ksi) = 2060,1440 = 1440 lbs Per ACI 530, Section 5.14.2.4,the combined ratio is B. +b <1.33(with1/3increase for wind/seismic) Bt Bv where: bt = ActualBoltTension bv = Actual Bolt Shear Bv = Allowable Bolt Shear Bv = AllowableBoltTension 35 of 44 VI -E.80 Enaineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures January1995 Elevation Sample Calculation Step 7: Design SillSole Plate Elevation Sample Calculation Forthis case, (560/800) + (900/1440) = 0.7 + 0.625 = 1.33 O.K. Therefore, use 7/8" 4A307 anchor bolts @ 2'-0" o.c. Embed a minimum of 4 inches. Center in cell of masonry. (The embedment of 4 inches works for the headed anchor bolt and is the minimum required for a reinforced wall with a bond beam at the top ofthe wall. However, embedment of up to 18 inches is common practice in the engineering industry for hooked anchor bolts.) Step 7: Design sill/sole plate Assume Southern Pine -pressure treated 2x8, No.2 grade 19% moisture content Per UBC Table 25-A-1 (and National Design Specification for Wood Construction), the following parameters are defined as: F l = tabulated compression design value perpendicular to grain = 565 psi Fb= tabulated bending design value = 1400 psi VF= tabulated shear design value parallel to grain (horizontal shear) = 90 psi E = modulus of elasticity = 1,600,000psi F = tabulated compression design value parallel to grain = 1200 psi C Check Bending Stress Average uplift per foot in area of concern, = 0.28 kip/ft Worst bending stress will occur at a splice or end of sill plate. Note that RI is critical due to prying action. Section modulus at bolt, Sy is Sy= Smember bolt hole Sy =2.719 -bh2/6 Sy =2.719 -(1"1)(1.5"1)26 S= 2.344 in3 36 of 44 Pnninoarinn Prinecinioeand Practices nf RltrofittinnFlnnd-Prnne Residential Structures VI -E.81 January 1995 Chapter VI: General Design Practices Elevation Elevation Sample Calculation The allowable bending stress, Fb' is givenby F.' = F.CdC tCCCCCCCCn b b d m t L F Y fU r C f where: Fb -Tabulated Bending Stress Cd = LoadDurationFactor C = Wet Service Factor Ct = Temperature Factor = Beam Stability Factor CL CF = Size Factor Cv = Volume Factor Cfu = FlatUse Factor Cr = Repetitive Member Factor Cr = Curvature Factor Cf = Form Factor For this example, (Reference: National Design Specification for Wood Construction) Cd = 1.6 Cf =1. 15 all other factors = 1.0 thus, Fb' = 1.6(1.15)(1400psi) = 2576 psi >>> fb O.K. in Bending 37 of 44 VI -E.82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 7: Design SllISole Plate Elevation Sample Calculation Check horizontal shear, f VQ lv Ib where: V Shear at Point Under Consideration Q = First Moment of Area Above Plane Under Consideration I = Moment of Inertia b = WidthofMember For this example, Q = 7.25(1.5/2)(1.5/4) = 2.04 in3 I Imember Ibait hole I = 2.039-(1"#)(1.5")3/12 = 1.76in4 V = RI z 600 lbs thus, = (600)(2.04) / (1 .76)(7.25) = 95.9 psi Allowable horizontal shear is given by, F -FCdCCtCH where: Fv = Tabulated Shear Stress Cd = Load Duration Factor Cm = Wet ServiceFactor Ct = Temperature Factor CH = Shear StressFactor For this example, (Reference: National Design Specification for Wood Construction) Cd =1.6 all other factors= 1.0 thus, F,'=1.6(90psi) = 144psi 659 psi O.K. Check single shear wood to concrete connector (due to shear wall load). (Reference: National Design Specification for Wood Construction, Section 8.2.3.) 39 of 44 VI -E.84 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 7: Design Sil Sole Plate Elevation Sample Calculation 7/8" 4bolt connected to a southern pine (No. 2 grade) 2x8, load parallel to grain, tm 2t, where: t = Thicknessof Main Member t -Thickness of Side Member For this example, to= 2(1.5) =3.0 in t=1.5 in from Table 8.2A of National Design Specification for Wood Construction, Zil = 1160 lbs the allowable stress is, z11 = where: ZCdCrmCtCgCA For this example, Cd = Z Cd Cm Ct Cg CA 1.6 = = = = = = Tabulated Allowable Stress Load Duration Factor Wet Service Factor Temperature Factor Group Action Factor Geometry Factor all other factors = 1.0 thus, Z11= (1160 lbs)(1.6)= 1856lbs one bolt has a trib length of 2'-0" Vbolt= 450 lbs/ft (2') = 900 lbs 224 lbs O.K. Therefore, a single 2x8 sill plate is acceptable with 718" 4 A307 anchor bolts with type "N" washers at 2'-0" o.c. grouted into masonry. 41 of 44 VI -E.86 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Elevation Sample Calculation Step 7: Design Sill/Sole Plate E- Elevation Sample Calculation SAMPLE DETAILS Minimum Reinforcement Required by Code for Seismic Zone 2 .... .. : h b i t0 a~ lR;t0i i 14,ii: : d E ::i:u-4 i--:; it4: i W.4 O05 ARA0(005 4 O EDR M EmIJRIT 0 T l. -oO F4 " VCL~T RIA .3.... . NA.S.~~ ~ ~ ~ ~ ~ ~~~;;;b~iSWA 00 XMASONRY til -|-tiit;0-t-;MINIMUM ~W2ALLC 033)550O 4S l-t:0i I0N .ti-0yt-it-.t--0-;-REOUILREMENT$t-SEISMICiZONEiNo. 20 :g ; Sample Bearing Wall Detail *4 a 48' 0. C. (MIDDLE OF CORE) VERTICAL REINFORCEMENT (FILL CELLS AT REINFORCEMENT NEW C. M. U. MASONRYWALL WITHGROUT HORIZONTAL REINFORCEMENT HORIZONTAL BARS IN AS REOUIRED GROUT-FILLED BOND BEAM NEW 31W' CONCRETESLAB ON GRADE (TYP.) UNDISTURBEDGROUND SURFACE 3. O NOTE:SPLICE NEW BARS TO EXISTING '4 DOWELS IN FOOTING a 48' O.C. PROVIDE CLASS B GROUT-FILLED HOLLOW EMBED18' BELOW GRADE LAP FOR No. 4 MASONRYUNIT ALL CELLS OR BELOW THE FROST BAR FOR MASONRY LINE, WHICHEVER EXIST. CONC.-t. e- DEEPER (TYP.) IS FOOTING J.., .. : l NOTE: INFORMATION SHOWN ON THIS DETAIL 4 / 71 P iNS TO 1THE CONTINUOUSREINFORCEMENT-~'VA" \ >m BLEM -' J. EXAMPLE PROBI REGUIRED IF ON FILL No. 4 HORIZONTAL BARS AT 24' O.C. WHEREREOUIRED il 2'-0" BEND ALTERNATE BARS HOLLOW-MASONRY UNIT EXTERIOR FOUNDATION WALL I B 1 2 3 42 of 44 VI-E.87 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.87 January 1995 Chapter VI: General Design Practices Elevation E, Elevation Sample Calculation Sample Foundation Detail .................. . ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. ....... ... .. ,,,~.',, -.:'jSOLEPLAT 'i'-- :::: ,1J,.' ' ' SLA TE OW M ...' 85 WIT O UT AL GAG ,.' . "'.'' 'N . .(' f t' :L''''',''W' . ''5: ' ' ZEW'FLOOR:'~m -- FiLL I:FTLOUt E- . 'WALLS-Y'ST:EMAANC'HANCH VI~~~~~~~~~HAHNPieOsadPacie fRetoitn lQ-Paa ai~~5nl.+rrila2 EaiLrn-.8 J Sa l De43 of 44 W VIE.88-Enalnearina PrincinitasD n P-SB R tfLV January 1995 Elevation Sample Calculation Step7: Design Sil/Sole Plate x VIZT-' C Qt] Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures VI -t.Yw January 1995 j j / Chapter VI: General Design Practices Elevation CONSTRUCTION CONSIDERATIONS PRIOR TO LIFTING ANY HOUSE Guidanceon * Obtain all permits and approvals required. Guidance on the selection of an elevation or relocation contractor eisprovided in Chapter VI-R, * Ensure that all utility hookups are disconnected (plumb sRelocation. ing,phone, electrical, cable, and mechanical). * Estimate the lifting load of the house. * Identify the best location for the principal lift beams, lateral support beams, and framing lumber, and evaluate their adequacy (generally performed by a structural engineer or the elevation contractor). SLAB-ON-GRADE HOUSE, NOT RAISING SLAB WITH HOUSE * Holes are cut for lift beams in the exterior and interior wall. * Main lifting beams are inserted. * Holes are cut for the lateral beams. * Lateral beams are inserted. * Bracing is installed to transfer the loads across the support walls and lift remaining walls. * Jacks are moved into place and structure is prepared for lifting. VI -E.90 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Construction Considerations * Straps and anchors used to attach house to slab-ongrade are released. * The house is elevated and cribbing installed. * Slab around edges is removed to allow for new foundation. * The new foundation is constructed. * New support headers and floor system are installed. * Any required wind and seismic retrofit is completed. * House is attached to new foundation. * All temporary framing is removed, holes are patched. * Reconnect allutilities. * Construct new stairways and access. * Floodproof all utilities below the FPE. SLAB-ON-GRADE HOUSE, RAISING SLAB * Trenches are excavated for placement of all support beams beneath slab. * Lifting and lateral beams are installed. * Jacks are moved into place and the structure is prepared for lifting. * The house is elevated and cribbing installed. VI -E.91 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -E.91 January 1995 Chapter VI: General Design Practices Elevation * The new foundation is constructed. * Any required wind and seismic retrofit is completed. * House is attached to new foundation. * Support beams are removed. * Access holes are patched. * Reconnect all utilities. * Construct new stairways and access. * Floodproof all utilities below the FPE. HOUSE OVER CRAWLSPACE/ BASEMENT * Remove masonry necessary to allow for placement of support beams. * Install main liftingbeams. * Install lateral beams. * Jacks are moved into place and the structure is prepared for lifting. * All connections to foundation are removed. * House is elevated and cribbing installed. * Existing foundation walls are raisedor demolished depending upon whether the existing foundation walls can handle the new loads. Vt -L.92 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Construction Considerations * New footings and foundation walls are constructed if the existing foundation walls/footings cannot withstand the additional loading. * Backfillbasement where appropriate. * House is attached to new foundation. * Support beams are removed. * Access holes are patched. * Reconnect all utilities. * Construct new stairways and access. * Floodproof all utilities below the FPE. HOUSE ON PILES, COLUMNS, OR PIERS If the house is to remain in the same location, the house will most likely need to be temporarily relocated to allow for the footing and foundation installation. If the house is being relocated within the same site, the footings should be constructed prior to moving the house. * Install main support beams. * Install lateralbeams. * Jacks are moved into place and the structure prepared for lifting. * House is elevated and cribbing installed. Prin-iAnlI f Retrofittina Flood-Prone Residential Structures January 1995 s1yiinaerinn and Prantices a VI -E.93 Chapter VI: General Design Practices Elevation o If the house is being relocated, see the Chapter VI relocation section. • House is attached to new foundation. * Remove support beams. * Reconnect all utilities. * Construct new stairways and access. * Floodproof all utilities below the FPE. VI -E.94 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Relocation Table of Contents Step 1-Selection of a House Moving Contractor .................................... VI -R.3 Experience .................................... VI -R.3 - Financial Capability.................................... VI R.3 ProfessionalismandReputation .................................... VI -R.3 Cost of Services .................................... VI -R.4 Step 2 -Analysis of Existing Site and Structure ..................................... VI -R.6 LiffingBeam Placement .......... . ............................................ . ............... ..... VI-R.7R.7............. Step 3 -Selection, Analysis, and Design of the New Site .................................... VI -R. 10 SiteAccess .................................... VI -R.10 Permits.................................... VI -R.10 Step 4 -Preparation ofthe Existing Site .................................... VI -R. 11 Step 5 -Analysis and Preparation ofthe Moving Route ............. ....................... VI -R. 12 IdentifyRouteHazards ..................................... VI -R.12 ObtainApprovals ..................................... VI -R.13 Coordinate Route Preparation .................................... VI -R. 13 Step 6 -Preparation of the Structure..................................... VI -R.14 DisconnectUtilities.................................... VI -R. 14 Cut Holes in Foundation Wall for Beams .................................... VI -R. 14 InstallBeams .................................... VI -R.15 Install Jacks ..................................... VI -R.15 EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures Vi -R.i January 1995 Install Bracing as Required ............................... VI -R. 16 Separate Structure from Foundation .................................. VI -R. 16 Step 7 -Moving the Structure .................................. VI -R. 17 Excavate/Grade Temporary Roadway .................................. VI -R. 17 Attach Structure to Trailer .................................. VI -R. 18 Transport Structure to New Site .................................. VI -R.2 1 Step 8 -Preparation ofthe New Site .................................. VI -R.22 DesignFoundation .................................. VI -R.22 DesignlJtilities.................................. VI -R.22 Excavation and Preparation of New Foundation ........... ....................... VI -R.22 Construction of Support Cribbing .................................. VI -R.23 Construction of Foundation Walls .................................. VI -R.24 Lower Structure onto Foundation .................................. VI -R.24 Landscaping .................................. VI -R.25 Step 9 -Restoration of Old Site .................................. VI -R.26 Demolishand Remove Foundation andPavement . ................................. VI -R.26 DisconnectandRemoveAll Utilities .................................. VI -R,26 Grading and Site Stabilization .................................. VI -R.27 VI -R.ii Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 RELOCATION Relocation is the retrofitting measure that can offer the greatest security from future flooding. It involves moving an entire structure to another location, usually outside the floodplain. Selection of the new site is usually conducted by the homeowner, often in consultation with the designer to ensure that critical site selection factors such as floodplain location, accessibility, utility service, cost, and, of course, homeowner preference meet engineering and local regulatory concerns. Relocation as a retrofitting measure not only relieves future anxiety about flooding, but also offers the opportunity to eliminate future flood insurance premiums. Figure VI-RI: House Relocation Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -R.1 January 1995 Chapter VI: General Design Practices Relocation The relocation process, as illustrated in Figure VI-R2, is fairly straightforward, but there are a number of design considerations to be addressed before embarking on this retrofitting measure. The steps involved with the relocation of a structure are discussed in more detail throughout this chapter: Step 1: Selection of a House Moving Contractor Step 2: Analysis of Existing Site and Structure Step 3: Selection, Analysis and Design of New Site Step 4: Preparation of the Existing Sitel Step 5: Analysis and Preparation of the Moving Route Step 6: Preparation of the Structure Step 7: Moving the Structure Step 8: Preparation of the New Site Step 9: Restoration of the Old Site Figure VI-R2: Relocation Process VI -R.2 Enaineerina Princinlas and Prarticesnf Ratrmfiftinet Rai U|UI5 …trL 9 ir.eiona January 1995 Step 1 -Selection of a House Moving Contractor STEP 1 -SELECTION OF A HOUSE MOVING CONTRACTOR The selection of a moving contractor is one ofthe most impor tant decisions a homeowner will make and may ultimately have the greatest impact on the success of the project. The designer can assist the homeowner in selecting an experienced home moving contractor. Some ofthe key elements ofthis selection (outlined in the Relocation Contractor Selection Checklist, Figure VI-R3) include: EXPERIENCE The designer/homeowner should visit recent projects the contractor has completed and talk to owners who recently went through the process to develop an opinion on the quality of work done by the contractor. FINANCIAL CAPABILITY The homeowner/designer should determine whether and to what extent the contractor is licensed, insured, and bonded. A prudent homeowner will consider the potential risk of a failed project before enlisting the assistance of a contractor. PROFESSIONALISM AND REPUTATION The International Association of The designer/homeowner may wish to check the Structural Movers (ISM) may be , contactedat:P.O.Box 1213, contractor's reputation with the state licensig board, the Elbridge,NY 13060, (315)689-local Better Business Bureau, local officials, and/orthe 9498,to obtain informationon International Association of Structural Movers (ISM). A houserelocationcompaniesfora critical question is whether or not the contractor is licensed retrofittingproject. to work in your area. Mnninnnrinn Print-inloa and Practircs nf Ratrnfiffinn Flond-Prona Residential Structures VI -R.3 January1995 Chapter VI:General Design Practices Relocation The designer/homeownershould also interview several contractors to determine: * how well they may be able to work with this individual; * the extent of the contractor's knowledge; and I what confidence may be had in the contractor's ability to complete the relocation project. COST OF SERVICES While this should not be the sole determinant of contractor selection, cost of services is an important aspect of the relocation process. To ensure a comparison of similar levels of effort, the designer/homeowner should develop a detailed scope of services to be provided and have each contractor prepare a bid from the same scope of services. Remember, the most qualified contractor may not always have the highest cost and conversely, the least qualified contractor may not have the lowest cost. VI -R.4 Engineerinq Principles and Practices of Retrofitting Flood-Prone Residential Structures January1995 Qtgn I . Qalao-tinn nf a House MnvinnCnntractnr Relocation/Elevation Contractor Selection Checklist F 1. Experience of the Contractor: Recent, successful house relocation/elevation projects? Yes No Satisfied clients providing good references? Yes__ No Met time schedules? Yes No Cleaned up and restored old site? Yes No Quality product through your visual inspection of recent projects? Yes__ No 2. Financial Stability of Contractor: Bonded? Yes_ _ No ; Amounts:_ Licensed? Yes__ No ; Amounts: Insured? Yes _ No ; Amounts:_ 3. Professionalism and Reputation of Contractor: State Licensing Agency: Better Business Bureau: LocalOfficials:_ International Association of Structural Movers: Results of the Interview:_ 4. Cost of Services: 5. Summary of References:_ I Figure VI-R3: Relocation/Elevation Contractor Selection Checklist - Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures VI--. 0 January 1995 L % > Chapter VI: General Design Practices ~~~Relocation STEP 2 -ANALYSIS OF EXISTING SITE AND STRUCTURE The designer should help the homeowner to ensure that the contractor conducts an analysis of the existing site and structure to determine the critical criteria for the relocation of the structure. These criteria will include: * Does sufficient space exist around the structure for the installation of lifting beams and truck wheels? A tP * Can the structure be lifted as one piece or must it be separated into sections? Usually this analysis is conducted * Dependingupon the final assessment of the structure's by the moving contractor and not conditions, how much bracing will be required to suc- by the homeowner's designer. However, it is important that the cessftlly move this structure? designer/homeowner coordinate and communicate with the * Will this structure survive the lift and a move of the contractor regarding the afore- distance proposed by the homeowner? mentioned issues. * Which utilities must be disconnected and where? * What local regulations govern demolition of the remaining portions of the structure (foundation and paved areas) and to what standard must the site be restored? The contractor usuallyhas experience in analyzing the existing structure to determine: * the size andplacementofliftingbeams,jacks, andlateral or cross beams; * whether the structure should be elevated/moved in one or several pieces. VI -R.6 Enaineerino Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 If the selected contractor is not familiarwith these factors, the homeownerand designer might reconsider their contractor selection. Step 2 -Analysis of Existing Site and Structure The final decision on these items may not be made until an evaluation of the moving route is conducted. LIFTING BEAM PLACEMENT Each of the following factors affecting the placement of lifting beams must be taken into consideration during the elevation and relocation process: * size and shape of the house; * existing framing and structural parameters; * deflection limitations; and * distribution of the structure's weight. The major consideration for the placement of lifting beams is to limit cracking due to excessive deflections during preparation, moving, and settling in place. The lifting beams, in tandem with cross or lateral beams, must provide sufficient support for the structure. When the house is removed from the foundation, the lifting and lateral beams should provide as stable a support as the original foundation. Deflection of any portion of the structure is normally a result of the manner in which the weight of the house is distributed, the location of the jacks under the lifting beams, and the rigidity of the lifting beam. Proper placement of lifting beams, jacks, and lateral beams will protect against cracking of both the interior and exterior finishes, as well as ensure the integrity of the entire house. Enaineerina Principlesand Practices of Retrofittina Flood-ProneResidential Structures VI -R.7 January 1995 Chapter VI: General Design Practices Relocation A second consideration concerning the installation of lifting beams is to ensure that they are located so that the house can be attached to truck wheel sets forming a trailer. The route to be taken during the relocation of the house dictates the physical size and weight limitations of the structure, due to the horizontal and vertical clearances from obstructions. The house may have to be cut into sections, which are moved separately to negotiate the available route. Lifting beams, therefore, would have to be placed for each section to be moved. The entire elevation framing must also be rigid enough to take the forces associated with movement. The weight of heavier construction materials on certain portions of the structure, such as brick veneer, chimneys, and fireplaces, causes additional deflection and warrants special attention when determining the lifting beam system. Even with minimal deflection, brick construction is subject to cracking. Therefore, extra precautions will be needed in the form of additional beam support or removal of the brick for possible later replacement. The size and shape of the house also affect the placement and number of lifting beams. A simple rectangular floor plan allows for the easiest and most straightforward type of elevation project. Generally, placement ofthe longitudinal VI -R.8 Enaineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 '44 :; IfL; I, t-gf Figure VI-R4: When a house is too planning is necessary in o the pieces separately. Step 2 -Analysis of Existing Site and Structure lifting beams, with lateral beams located as required, is the system utilized for the elevation process. Larger or more complex shapes, such as L-shaped or multi-level homes, necessitate additional lifting beams and jacks to provide a stable lifting support system. Every consideration of the load based upon the size and shape of the structure should be incorporated into the design and layout of the lifting beam system. large to be relocated in one piece, careful irder to cut the structure in pieces and move Enaineerina Princinles and Practices of F 4etrofittina Flood-ProneResidential Structures VI -R.9 Ja y ____ . -1 9 5 -O -_ January 1 995 Chapter VI: General Design Practices 7 <\ ~ Relocation STEP 3 -SELECTION, ANALYSIS, AND DESIGN OF THE NEW SITE The selection of a new site for a relocated house will require-WI the examination of potential sites with regard to: Information on site design * floodplain location; standards may be obtained from the local building official, or, if there is none, from a HUD publica-* utility extensionfeasibility; tion entitled, Proposed Model Land DevelopmentStandardsand * accessibility;and Accompanying State Enabling Legislation, 1993 Edition. * permitting feasibility. The process is similar to selecting a lot upon which to design and build a new home. Local building codes and approval processes must be followed. In some instances, the homeowner may be required to upgrade existing me chanical, electrical, and plumbing systems to meet current code requirements. SITE ACCESS An important consideration in the selection of a new site is the accessibility of the site for both the house movers and the new site construction crews. Severe site access con straints can increase the cost of the measure and/or require clearing and grading activities, which maydiminish the site characteristics the homeowner initially desired. PERMITS The designer/homeowner should make certainthat when the house is moved to the new lot, it will conform to all the zoning and construction standards in effect at the time of relocation. The designer should contact the local regulatory VI -R.10 Enaineerina Principlesand Practicas of Ratrmfittinn Flood-Prone RamirigntiaIl Qtrt4irt iras -v_ g ~---e .--...... a -w * 1995 --r *.g-~-Wwe *Jau-ar *w * EwV January 1 995 Step 4 -Preparation of the Existing Site officials to determine the design standards and submission process requirements that govern development of a new site. All permits required for construction at the new site and for transporting the structure to the new site should be obtained prior to initiating the relocation process. STEP 4-PREPARATION OF THE EXISTING SITE The initial preparation ofthe site includes clearing all vegetation from the area in and around the footprint of the house. This is done to clear a path beneath the structure to allow the insertion of beams for lifting supports. These pathways should be deep enough to allow for the movement of both people and machin ery. Figure VI-R5: Clearing Pathways Beneath the Structure for Lifting Supports EngineeringPrinciplsandPrcticesfRetrofttinFoodPronResidetialStrcturI I R Eniern ricpe n Patie ofRtoitn lo-rn eieta tutrsV -R1 January 1995 Chapter VI: General Design Practices 7

Dry Floodproofing INSPECTION AND MAINTENANCE PLAN Every dry floodproofing system requires some degree of periodic maintenance and inspection to ensure that all components will operate properly under flood conditions. Components that should be inspected as part of an annual maintenance and inspection program include: * All mechanical equipment such as sump pumps and generators; * Flood shields, to ensure that they fit properly and that the gaskets and seals are in good working order, properly labeled, and stored where accessible; and * Sealed walls and wall penetrations, for cracks and potential leaks. _. ,; s ---of Rptrnfittinn Fln-nPrPnna >iuvuett QIUL&UIr+ CO VI -D.4 Enaineerina PrinciolesandPranfimce-..._ ..... .. _z-* .----, .w Iv$ t~*%JvI faoirlantilo OCtrnnhi January 1995 Sealants and Shields SEALANTS AND SHIELDS Sealantsand shields are methodsthat can be used to protect a structure from low-level flooding. Mini-floodwalls (low level) can be used as an alternative to shields for protection of windows, window wells, or basement doors. These systems are easily installed and can be inexpensive in relation to other measures such as elevation or relocation. However, by sealing (closing) a structure against flood inundation, the owner must realize that, in most cases, the typical building will not be capable of resisting the loads generated by more than a few feet Floodwallsandfloodwallclosures of water. There will be a point beyond which the sealants and are discussed in Section F of this shields may do more harm than good and the owner must allow chapter. the building to flood to prevent structural failure from unequalized forces. The U.S. Army Corps of Engineers,National Flood Proofing Committee, has investigated the effect of various depths of water on brick veneer-over-wood and masonry walls. The results of their work show that, as a general rule, no more than three feet of water should be allowed on a brick veneer wall or ona non-reinforced concreteblockwallthathas not previously been designed and constructed to withstand flood loads. While no definitive research on floodproofing wood-frame walls without brick veneer facing has been undertaken, it is generally accepted that wood-frame houses will fail at a lower water depth than a masonry or brick veneer home. Therefore, application of sealants and shields should involve a deternination of the structural soundness of a building and its corresponding ability to resist flood and flood-related loads. Sealants include compounds that are applied directly to the surface ofthe structure to seal exterior walls and floors, or a wrapthat is anchoredto the exteriorwallor foundation ator below the ground and attached to the wall above grade during flooding. The owner may wish to add to the structural strength ofthe existing building to aid in resisting flood-induced loads (for example adding a brick veneer). - Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI D.5 January 1995 Chapter VI: General Design Practices Dry Floodproofing Any dry floodproofing system can be expected to allow some water infiltration, and the owner should have a dewatering system capable of removing the water. Due to this infiltration through exterior walls and floors and percolation ofthe water around ground anchored wraps, these systems are not recom mended for situations where floodwater is in contact with the building for more than 12-24 hours. Underlying soils often dictate the allowable period of inundation before water starts to percolate through the sealant system. Existing Brick Veneer Sheathing Brick Rowlock ,Wood Frame Wall or CMU Block Wall Flood Protection Elevation\ C s F f reebo ard) ~~(includes : New Brick Work -Metal Fasteners Coating and Waterproofing Tie New Brick to Old Brick Add Concrete Footing ting Drill and Grout Drain to Sump Pump with Connection to Backup Power Source Existing Footing Figure VI-D2: The best way to seal an existing brick-faced wall is to add an additional layer of brick with a seal in between. Just sealing the existing brick is also an option. VI -D.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sealants and Shields -A1--A _-V L< Flood Protection Elevation 'WI, (Includes Freeboard) 1 Freeboard Sheathing V, Flood Elevation Attach to House Wood Frame Wall 6 Mil. Polyethylene Place Loosely on Wall _ Z Brick Veneer 4' PVC Perforated Pipe (Drain to Sump with Backup Power Source) Sand Bags Loose Sand Slabto Monolithic and Footing Figure VI-D3: A wrapped house sealing system can be used to protect against low level flooding. Shields are watertight structural systems that bridge the openings in a structure's exterior walls. They work in tandem with the sealants to resist water penetration. Steel, aluminum, and plywood are some of the materials that can be used to fabricate shields. These features are temporary in most cases, but may be permanent when in the form of a hinged plate or a mini- floodwall at a subgrade opening. Shields transfer flood-induced forces into the adjacent structure components and, like sealants, can overstress the structural capabilities ofthe building. EnnineerinnPrincinles and Practices of Retrofittina Flood-Prone Residential Structures VI -D.7 January 1995 Chapter VI: General Design Practices Dry Floodproofing Figure VI-D4: A shield hinged at its bottom could prevent low-level flooding from entering a garage or driveway. Shield e 1' Freeboard Panel Shield Track Figure VI-D5: A door opening may be closed using a variety of materials for shields. Vi -D.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sealants andShields Connection Figure VI-D6: A shield can help prevent low-level flooding from entering through a doorway. Figure VI-D7: Where a window is exposed to a flood, bricking up the opening could eliminate the hazard. The use of sealants and shields requires that the house have a well-developed interior drain system to collect the inevitable leaks and seepage that will develop. This means establishing drains around footings and slabs to direct seepage to a central collection point where it can be removed by a sump pump. Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -D.9 January 1995 Chapter VI: General Design Practices Dry Floodproofing Additionally, abuilding employing sealants and shields will usually need backflow devices and other measures designed to eliminate flooding thiugh utility system components. Additional information on this topic is presented later in this section. - Never seal a floodprone basement unless a Lower level should only be structural analysis indicates the structure can used for parking, storage, withstand flood and flood-related loads. and access. l~~~~~~~~~~~------ Ie Ela Hi lzr Downspout Aiii -__ ___ii' r ->1 Fr ) Sunppurnp (' -ii C.")i' ") ll-4 ( 2 2 J< dischargeFP AIL ,Jim Footing drain _1 l ~~~~~~~d~r~ain i nfreeboard) TT-~Floor drain I _ Footing ANAL~~ H1lr, Sanitarysewerserviceline Back'lowvalve Figure VI-D8: Dry floodproofed homes should have an effective drainage system around footings and slabs to reduce water pressure on foundation walls and basements. VI -D.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sealants and Shields Drain System Around a House : | 1.'".' s %7I V 9 I 4" Non-Compacted Gravel, Pipe to Sump Crushed Stone Footing Drai _ional 4 Footing -> Waterproofing \ Sewer Backup Valve 4" Compacted Gravel, Crushed Stone Underdrain \ Sump Pump with Backup Power Source Figure VI-D9: Drain System Around a Slab-on-Grade House Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.11 January 1995 Chapter VI. General Design Practices () 3 > DryFloodproofing FIELD INVESTIGATION In addition to, or during consideration of, the field investigation information compiledon the existing building/building systems data sheet (Figures VI-3 and VI-4), the designer should concentrate on collecting or verifying the following items: * condition of existing framing, foundation, and footing; * determination of existing materials used in the house to calculate dead weight; * determination oftype of soil, lateral earth pressures, permeability, and seepage potential; * building's lateral stability system and adequacy of structural load transfer connections; * foundation wall, footing, and slab information (thicknesses, reinforcement, condition spans, etc.); * number, size, and location of openings below the FPE; * expected flood warning time; * evidence of previous, and potential for continued, settlement, which could cause cracking after sealant is applied; * estimates of leakage through the exterior walls and floor; e manufacturer's data to determine applicability of sealant materials in terms of above- and below-grade applications, and duration of water resistance; * potential anchorage to secure wrapped systems; VI -D.1 2 Enoineerina Princinies and Practices of Retrmfittinri Flood-Prone PRsidlentialSt intiirum D_ __ wry a . . v. ._ . .__.__ .. l.Hanuar-199 -+;s January 1 995r Field Investigation * preliminary selection of shield material to be used based upon the length and height ofthe openings and duration of flooding; and * preliminary selection oftype of shield anchorage (hinged, slotted track, bolted, etc.), to be utilized by considering accessibility, ease of installation, and amount oftime available for installation. Using this information, a designer should be able to determine if a system of sealants and shields is an option. Of course, further calculations or conditions may dictate otherwise, or that modifications should be made to accommodate the system. The designer can take the information gathered in the field and begin to develop type, size, and location alternatives. Sealant alternatives include: * cement-and asphalt-based coatings, epoxies and polyurethane- based caulks/sealants; * membrane wraps such as polyurethane sheeting; and For additional information concerning the performance of various sealant systems, refer to the U.S. * brick veneers over a waterproofcoating on the existing Army Corps of Engineers research foundation. study entitled Flood Proofing Tests, August 1988, and product Shield alternatives include: evaluation reports prepared by model code groups. * a permanent low wall to protect doors and window wells againstlow-levelflooding; * bricking in a nonessential opening with an impermeable membrane; * drop-in, bolted, and hinged shields that cover an opening in the existing structure. Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -D.1 3 January 1995 Chapter VI: General Design Practices < m Dry Floodproofing Shield alternatives that require human intervention should be considered only ifthe flooding situation provides sufficient warning time to properly install the shields. The need for both sufficient warning time and "human intervention" is critical, since shield systems usually require personnel to install them and make certain they are properly connected. DESIGN CONFIRM ABILITYOF STRUCTURE TO ACCOMMODATE DRY FLOODPROOFING MEASURES A critical step in the development of initial type, size, and location ofthe sealant and shield systems is to determine the ability ofthe existing framing and foundation to resist the expected flood-and non-flood-related forces. This process is illustrated in Figure VI -D 1 0: Existing Building Structural Evaluations. Step 1: Calculate flood and flood-related forces. The calculation of flood and flood-related forces (hydrostatic, hydrodynamic, debris impact, soil, and buoyancy forces) as well as determination of seepage and interior drainage rates) was presented in Chapter IV. The designer should account for any non-flood-related forces (i.e., wind, seismic, etc.) by incorporating those forces into Steps 2-6. The determination of non-flood related forces was presented in Chapter IV. VI -D.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Existing Building Structural Evaluations Calculate Flood and I Flood-Related Forces I Figure VI-D 10: Existing Building Structural Evaluations Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI -D.15 January 1995 Chapter VI:General Design Practices K K Ž< Dry Floodproofing Step 2: Checkflotation ofthe wood-frame superstructure. Residential structures that are determined to be watertight should be checked to ensure that the entire sub- and super structure will not float. However, it is reasonable to assume that most residential construction will fail prior to flotation ofthe structure. This failure will most likely occur through the slab- on-grade breaking (heaving/cracking), a window or door failing inward, or extensive leakage through wall penetrations. Should the designer wishto check the failure assumption, guidance is provided in Step 5. If floodwaters come into contact with a wood floor diaphragm (elevated floor or crawlspace home) the floor system/building superstructure should be checked for flotation. Check the sum ofthe vertical hydrostatic (buoyancy) forces acting upward against the gravity forces (deadload) acting downward on the structure. The gravity forces acting down ward should be greater than the buoyancy forces acting up ward. If this is not the case, the designer should consider choosing another floodproofing method or designing an anti- flotation system. The homeowner should make this decision based upon technical and cost information supplied by the designer. Step 3: Check ability of walls to withstand expected forces. Frames and connections for closures transfer the retained forces The typical failure mode for a into the adjacent walls. Typically a vertical strip on each side of shield installation is the "kick-in" the opening must transfer the load up to a floor diaphragm and of the bottom connection where down to the floor or foundation. This "design strip," shown in hydrostaticforces are the greatest. Figure VI-D 11,must be capable of sustaining loads imposed on itself and from the openings. The designer should consider all forces acting on the design strip, as well as the following additional considerations: a. Checkdesign strip based on simple span, propped cantilever, cantilever, and other end conditions. Consider the moment forces into the foundation. VI -D.16 Enaineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures January 1995 Design Effective design strip width based on building code Figure VI-D I 1: Typical Design Strip b. Check design strip for bending and shear based on concrete, wood, masonry, or other wall construction. c. Consider the path of forces from shield into the design strip through the various connection alternatives including hinges, drop-in slots, frames, and others. d. The designer may want to refer to the American Institute of Steel Construction (AISC) Steel Manual, American Concrete Institute (ACI) documents for concrete and masonry construction, National Design Specifications of Wood Construction (NDS)/ American Institute of Timber Construction (AITC) documents for timber construction, APA documents for plywood, and other applicable codes and standards for more information on the ability of these materials to withstand expected flood and flood-related forces. Fnnineerina Princioles and Practices of FletrofittinaFlood-Prone Residential Structures VI -D.17 January 1995 Chapter VI: General Design Practices Dry Floodproofing Step 4: Check ability of footing to support veneer applications. The application of veneer to the exterior of an existing wall must be supported at the footing level. The designer should consider all forces acting on the existing footing, as well as the following additional considerations: a. Supporting the masonry veneer on an existing footing can add an eccentric load onto the footing and can create soil pressure problems. The designer should analyze the footing with the additional load considering all load combinations including the flooded condition. b. The actual pressure on the footing should not overload the bearing capacity of the existing soils. Consult a geotechnical engineer, ifnecessary. c. The designer may want to refer to the ACI Manual for Concrete Construction, various soils manuals/textbooks for detailed footing design, and applicable codes and standards. Step 5: Check slab and connections against uplift forces. As floodwaters rise around a structure, a vertical hydrostatic (buoyancy) force builds up beneath floor slabs. For floating slabs, this buoyancy force is resisted by the structure dead load and saturated soil above the footing; for keyed-in slabs, this buoyancy force is resisted by the structure dead load, and the flexural strength ofthe slab. These slabs must be capable of spanning from support to support with the load being applied beneath the slab (see Figure VI-D 12). The designer should consider all forces acting on the existing slab and connections, as well as the following additional considerations: VI -D.18 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Figure VI-D 12: Typical Slab Uplift Failure a. Verify the existing slab conditions including thickness, reinforcement,joint locations, existence of continuous slab beneath interior walls, existence of ductwork in slab, and edge conditions. If reinforcement and thickness are not easily determinable, make an assumption (conservative) based on consultation with the local building official or contractors. b. Confirm the slab design by checking reinforcement for bending and edge connection for shear load. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.19 January 1995 Chapter VI: General Design Practices /X()Dry Floodproofing Step 6: Check stability oftop offoundation wall connections. Foundation walls may retain water in some situations. These walls must transfer the additional hydrostatic load down to the footing or slab and up to the floor diaphragm. The designer should consider all forces acting on the top ofthe existing foundation wall connections, as well as the following additional considerations: a. Verify existingwall conditions including construction material, reinforcement, design conditions (simple span, propped cantilever, cantilever, and other end conditions), and connections. b. Connections between the wall and floor are of major importance in consideration ofthe wall stability. The designer should check the following: 1. masonry/concrete for shear from bolt; 2. anchor bolt for shear; 3 . sill for bending from bolt loads; and 4. transfer of load from sill intojoists into plywood diaphragm. 5. Loads have a pathway out ofthe structure. Additional bracing and/or connectors may be required to provide this pathway. Analyze framing and be cognizant that all sides may be loaded. c. The designer may want to refer to the ACI Manual for Concrete Construction, ND S/AITC for timber construction, AISC for anchor bolts, product literature for wood connectors, and applicable codes and standards. VI -D.20 Engineerina PrinciDles and Practices of Retrofittino Flood-Prone Residential Structures January 1995 Design - Step 7: Design foundation supplementation system, as required. If the checks in Steps 2-6 determined that any structural members were unable to withstand expected flood and flood- related loads (wind, seismic, and other forces can be evaluated as presented in Chapter IV), the designer can either select another retrofitting measure or design foundation supplementation measures. These foundation supplementation measures could range from increasing the size of the footing to adding shoring to the foundation walls, or simply modifying the type, size, number and location of connections. The homeowner should make this decision based upon technical and cost information supplied by the designer. Footing Reinforcing: in some cases, the footings for walls must be modified to accommodate expected increased loadings. The following considerations should be taken into account during the design ofthis modification: a. The wall footing must be checked for the increased soil pressure and sliding. Moment and vertical loads from the wall above should be added. b. The footing may need more width and reinforcement to distribute these forces to the soil. c. For some extreme cases (poor soils, high flood depths, flood-related wind and/or earthquake loads), a geotechnical engineer may be required to accurately determine specificsoil loads and response. d. The designer should consider multiple loading situations taking into account building dead and live loads that are transferred into the footing, utilizing whatever load combinations are necessary to design the footing safely and meet local building code requirements. Consider the framing of the structure andhow the entirehouse load is transferred into the foundation. Pnninnnrmni Prin-inl=s and Practices of Retrmfiftinn Flood-Prone ResidentialStructures VI -D.21 Januayll IIIV 1 1 | I V A IVV 1995| January 1 995 ChapterVI: GeneralDesign Practices < k~ DryFloodproofing Dry floodproofing measuresare only as good as their weakest link (i.e., the connection to the existing structure). The designer should ensure that all appropriate details for making theconnectionwater- tight as well as allowing for the transfer of loads are developed. e. The designer may want to refer to the ACI Manual for Footing Design, recent texts for wall and footing design, and applicable codes and standards. Step 8: Repeat process in Steps 1-7 incorporating exterior wall foundation supplementation system. Once the designer has detenminedthat the existing framing and foundation are suitable forthe application ofsealants or shields, or that reinforcement can be added to make the existing framing and foundation suitable for te application of sealants or dosures, the selection/design of a specific system can begin. VI -D.22 Enaineerina Principles and Practices of Retrofittino Flond-Prone Resirintili Striinti res January 1995 Selection and Design of Sealant Systems SELECTION AND DESIGN OF SEALANT SYSTEMS Once the determination is made that a foundation system can withstand the expected flood and flood-related forces, the selection of a sealant system is relatively straightforward and centers on the ability ofthe manufacturer's product to be com product performance, if available, patible with the length and depth of flooding expected and the should be used to supplement the type of construction matenalsusedin the structure. manufacturer's literature. Sources of test results include model COATINGS building code product evaluation C A I S reports, a USACE publication entitled Flood Proofing Tests, The selection of a coating follows the flow chart presented in August 1988, and local building Figure VI-Di 3, Selection of Sealants/Coatings. If additional code officials. structural reinforcing is required, it should be performed in accordance with the guidance presented in the preceding section entitled "Confirm Ability of Structure to Accommodate Dry Floodproofing Measures." r . nnnc ind ~ ,Drmiiem FlRood-ProneResidentialStructures VI-D.23 A -inlp of Rtrnfittinn Jauayl 1995ll v * w II IV I rVVI l January 1 995 ChapterVI: General Design Practices Dry Floodproofing Selection of Sealants/Coatings 1K Design Interior Drainage Collection System Figure VI-D 13: Selection of Sealants/Coatings WRAPPED SYSTEMS The selection and design of a wrapped system follows Figure VI-D 14, Selection and Design of a Wrapped Sealant System. If additional structural reinforcing isrequired, it should be performed in accordance with the guidance presented in the preceding section. VI-D.24 Engineering Principles and Practicesof Retrofitting Flood-Prone Residential Structures January1995 Selection and Design of Sealant Systems Selection and Design of Wrapped Sealant System Figure VI-D14: Selectionand Design of Wrapped Sealant Systems VI-D.25 Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -D.25 January 1995 Chapter VI: GeneralDesign Practices O9 > Dry Floodproofing Step 1: Selecttype and grade of material. Step 2: Checkmanufacturer'sliteratureagainstdurationand al-depthof flooding. For additional informationconcern-If flooding application is satisfactory, proceed with design; if not ingtheperformanceof various satisfactory, select another product or another method. sealant systems, refer to the U.S. Army Corps of Engineers research studyentitledFlood Proofing Step 3: Checkmanufacturer's literature forapplicabilityto Tests, August1988,andproduct building materials. Rely on actual test results, if evaluation reports prepared by available. model code groups. If building materials application is satisfactory, proceed with design; if not satisfactory, select another product or another method. Manufacturer performance claims can be misleading. The designer should utilize actual test results rather than rely entirely on a manufacturer's performance claim. Step 4: Check installation instructions for applicability. If installation procedure is satisfactory, proceed with design; if not satisfactory, select another product or another method. Step 5: Designconnectiontotopofwall. Adding a wrap system onto an existing structure will require secureconnections atboth the top and bottomofthe wrap. It is difficult to determine the actual loads imposed vertically on the wrap as this can vary based upon the quality of the installa tion. Voids left from poor construction may force the wrap to carry the weight ofthe water and should be avoided. See Figure VI-D 15. The following considerations should be followed during selection and design of a top-of-wall connectionsystem: VI -D.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structiures January1995 Selection and Design of Sealant Systems Figure VI-D15: Plan View ofWall Section a. Use a clamping system that uniformly supports the wrap. A smallspacingonthe connectionsand a member with some rigidity on the outside ofthe wrap can provide this needed support. b. The existing wallconstruction is an importantconsideration for these connections and canvary widely. Part of the connection may need to be a permanent part of the wall. See Figure VI-D3fordetails on wrapped system configuration. c. The designer may want to refer to the product literature for wrap material, NDS/AITC for connections into wood, and applicable codes and standards. Step 6: Designfoundationreinforcing. Refer to Chapter VI -Dry Floodproofing Section entitled "Confirm Ability of Structure to Accommodate Dry Flood- proofing Measures." Step 7: Design drainage collection system. Refer to Chapter VI -Dry Floodproofing Section entitled "Drainage Collection Systems." ResidentialStructures C^^;naar~n-D0-fn^ ,i f RQtrnfittinn Flonod-Prone VI -D.27 January 1995 Chapter VI:General Design Practices Dry Floodproofing Step 8: Specify connection of wrapping to existing structure and existing grade. Wrapsystemsmaybe affectedby Anchoring a wrap into the grade at the base of a wall will be the freeze-thawcycles.Careful most important link in the wrap system. The following considinstallationin accordancewith erations should be followed during selection and design of a manufacturerinstructionsand wrap to existing grade connection system: evaluation ofperformance in frozen climates is advisable. a. A drain line between the wrap and the house is required to remove any water that leaks through the wrap or that seeps through the soil beneath the anchor. b. As with the top-of-wall connection, wrap forces are difficult to determine. It is best to follow details that have worked in the past and are compatible to the specific structure. c. It is recommended that the end of the wrap be buried at least below the layer oftopsoil. Additional ballast may be needed (sandbags, stone, etc.,) to prevent wrap movement in a saturated and/or frozen soil condition. d. The designermaywantto referto theproductliterature for wrap material and applicable codes and standards. BRICK VENEER SYSTEMS The selection and design of a brick veneer sealant system follows Figure VI-D 16,Selection/Design of a Brick Veneer Sealant System, and has many components that are similar to SeeFigureVI-D2fordetailson the design of other sealant systems. A typical brick veneer brickveneersystemconfiguration. sealant system is shown in Figure VI-D2. Ifadditional structural reinforcing is required, it should be performed in accordance with the guidance presented in the preceding section. VI -D.28 Enaineering Principles and Practices of Retrofitting Flond-ProneRPsidentialStruirtu ires January 1995 Selection and Design of Sealant Systems Selection and Design of Brick Veneer Sealant System IV [--Prepare Plans and Specifications Figure VI-D1 6: Selection/Design of a Brick Veneer Sealant System Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.29 January 1995 Chapter VI:General Design Practices :N>s~ Dry Floodproofing Step 1: Check the capacity ofthe existing footing. Calculate the weight of the structure and proposed brick veneer system on a square foot basis and compare it to the allowable bearing capacity for the specific site soils. If the bearing pres sure from gravity loads is less than the allowable bearing pressure, the existing footing can withstand the increased loading. If the bearing pressure from gravity loads is greater than the allowable soil bearing pressure, the existing footing is unable to withstand the increased loading andthe footing must be modified, or the designer should select another floodproofing measure. Step lA: Supplementthe footing, as required. If it is found that the existing footing cannot support the loads expected from a veneer system or that the configuration ofthe footing is unacceptable, the footing can be widened to accom modate this load. This can be a costly and detailed modifica tion. The homeowner should be informed ofthe complexity and cost of such a measure. The following considerations should be followed during design ofa footing supplement: a. If additional width is added to the footing, the designer must analyze how the footing will work as a unit. Reinforcing must be attached to both the old and new footing. This will probably involve drilling andepoxy grouting reinforcement into the existing footing. The quality and condition ofthe existing concrete and reinforcement should be considered in the design. b. Exercise care when making excavations beside existing footings. Take carenotto underminethe footings, which could create major structural problems or failure. c. Design the footing for the eccentric load from the brick weight. Add any flood-related loads and consider all possible load combinations. VI-D.30 Enaineerina Principles and Practices of RPstrnfittin,FInnri-Prninc PoQ~RantimlQ+ri ntoirm* - ---_ -Ir------_-.--......~..-*anuary1995 January 1995 Selection and Design of Sealant Systems d. For extreme soilconditions, consult a geotechnical engineer to determine soil type and potential response. e. The designermaywant to referto the ACI Manualfor Concrete Design, a soils manual/textbook for detailed footing design, and to applicable codes and standards. Step 1B: Designfoundationreinforcing(asrequired). Concrete footings can come in a wide variety of configurations. Design offootings, especially those involved with retaining of materials, can become quite complex. There are many books that deal with the design of special foundations, and once the stresses are determined the ACI can provide guidelines for concrete reinforcement design. Steps 2-9 aresimilarto the designof wrapped sealantsystems. Refer to the previous section for details on these steps. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.31 January 1995 ChapterVI: General Design Practices Dry Floodproofing SELECTION AND DESIGN OF SHIELD SYSTEMS Once the determination is made that a foundation system can withstand the expected flood and flood-related forces, the selection of a shield system is relatively straightforward and centers on the ability ofthe selected material to structurally secure the opening, be compatible with the existing construction materials, and be responsive to the duration and depth of flooding expected. PLATE SHIELDS The selection and design of a plate shield follows Figure VI- Industryhas developedmanufac-DI 7, Selection/Design of Plate Shields. Ifadditional existingtured closuresystemsthatmaybe structural reinforcing is required, it should be performed in applicableto specificsituations, accordance with the guidance presented in the precedingFor additional information on the companies that manufacture these section. products, contact your local floodplainmanagementorengi-Step 1: Select the plate shield material. neering office. Plate shield material selection may be driven by the size ofthe opening or the duration of flooding. For example, plywood shields would not hold up during long-term flooding. a. Consider flood duration and select steel or aluminum materials for long duration flooding and consider marine grade plywood materials for short duration flooding. b. Consider opening size and select steel and aluminum materials with stiffeners for larger openings and shored plywood with appropriate bracing for small openings. c. Installation of all shields should be quick and easy. Lighter materials such as plywood and aluminum are most suitable forhomeowner installation. VI -D.32 Engineerina PrinciDlesand Practices of Retrofittino Flood-Prone ResidentialSiS iialruc January 1995 Selection and Designof Shield Systems Selection/Design of Plate Shields Prepare Details and Specifications Figure VI-D 17: Selection/Designof Plate Shields Step 2: Determine panel stresses. Thedesignershouldcheckthe shieldpanel eitheras a plate or a 46 horizontal/vertical span across the opening. The use of plywood shields in long-term exposure situationsmay a. Using end conditions and attachments to determine how the induce possible swelling and de-panel will work, calculate stresses based on bending of the terioration of the laminating glue. I ET ^^ VI- Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-Wd. January 1995 Chapter VI: General Design Practices & Y 7P Dry Floodproofing plate. In larger plate applications, also compute the end shear. b. Compare these stresses to the allowable stresses from the appropriate source. c. Some shieldsmay have a free end at thetop or other unusual configuration. These will need to be addressed on a case-by-case basis. d. Adjust the plate thickness to select the most economical section. If the plate does not work for larger thicknesses, add stiffeners. e. The designer may want to refer to the AISC manual for steelplate design, analuminum design manual,APA for plywood design, and applicable codes and standards. Step 3: Check deflections. A plate shield that is acceptable for stresses may not be acceptable for deflection. a. Calculate deflections forthe panel and evaluate on the basis of connections and sealants. b. If the deflection is unacceptable, add stiffeners. c. Deflection may be controlled by alternative plate materials. d. The designer may want to refer to the AISC manual for steel plate design, an aluminum design manual, APA for plywood design, and applicable codes and standards. VI -D.34 Enaineerino -a Princinles and Prantioss nf RPtrnfittinwFlond-Prnne RoioHntial Qtri itfi. -*-r-----v . .--* E .w [_|*v7Jauary1995January1995 Selection and Design of Shield Systems Step 3B: Stiffen as required. Plate overstress or deflection may be solved through the use of stiffeners. a. Select the section to be used as a stiffener. Angles may be used for steel or aluminum and wood stock for plywood. b. Calculate the stresses and deflection based on the composite section of stiffener and plate. c. Calculate the horizontal shear between the two sections and design the connections to carry this load. d. Keep plate connections and frame in mind when detailing stiffeners. e. The designer may want to refer to the AISC manual for steel plate design, an aluminum design manual, APA for plywood design, Mechanics of Materials tests, and applicable codes and standards. Step 4: Design the connections. Plate connections must be easy to install and able to handle the loads from the plate into the frame and surrounding wall. a. Determine the type of connection (hinged, free top, bolted, latching dogs, or other). b. Consider ease of installation and aesthetics. c. Connection must operate in conjunction with gasket or sealant to prevent leakage. d. Connection must be capable of resisting some forces in the direction opposite of surges. -------:InADr::ltaiog~ Flood-PronARAsidentialStructures January 1995 Cnnne_ in l e of Ratrnfittinn VI -D.35 ChapterVI: GeneralDesign Practices Dry Floodproofing e. The designer may want to refer to the AISC manual for bolted connections, ACI manual for connections into concrete and masonry, and applicable codes and standards. Step 5: Selectthegasketorwaterproofing. Gaskets or waterproofing materials, which form the interface between shields and the existing structure, are vital elements of the dry floodproofing system. They should be flexible, durable, and applicable to the specific situation. a. Determine the type of gasket orwaterproofmg required. b. Consider ease of installation and ability to work with plate/ connections as a single unit. c. Gasket/waterproofing must be able to withstand expected forces. d. Gasket/waterproofing must be able to fbinction during climatic extremes. e. The designer should refer to manufacturer's literature and check against duration/depth of flooding and applicability to selected building materials. Step 6: Checkadjacentwalls, lintels,sills,andtop/bottom connections. Structural components adjacent to the shield panel, such as adjacentwalls, lintels, sills, and top/bottom connections, should be checked against maximum loading conditions. Different methods of attachment may load the adjacent wall differently. VI -D.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Selection and Design of Shield Systems Walls adjacent to the shield should be anchored into the footing to resist base shear. Lintels/sills should be checked for biaxial bending resulting from lateral loading. Top connections should be evaluated for shear resistance and ability to transfer loads to thejoists. The following design example illustrates the process of selection and design of a window opening shield. rnt.tirlMa of Structures C~~nninaari-n O~innccnr RatrofittinnFlonri-Prone Residential VI -D.37 Januarlvvrlry l~lulv::iallu a .... __ 1995 ........ . ..__.__...._.-_..__._. January 1995 Chapter VI: General Design Practices Dry Floodproofing Sample Calculation for Shield Design GIVEN: Shield in 12-inch Concrete Masonry Unit wall subjectto hydrostatic (freestanding water) flood loading only. .'. . N'X N. N. ';.' N "v,--:. ?r9-aR>> 4519 psi O.K. 4 of 11 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.41 January 1995 Chapter VI: General Design Practices Dry Floodproofing Sample Calculation for Shield Design Step 3: maximum deflection, Ymax 0.04 + 0.05 = 0.09 in. maximum allowable deflection is recommended to be, Yellow = L/240 where: L = sWanofmemberunder consideration ,, _ for this example, Y.W = 40 in/ 240 = 0.17 in. > 0.09 in. O.K. Note: If deflection is a problem, stiffeners can be added to the plate. Step 4: CheckConnectiontoWall The reaction from the uniform load can be determined from the previous equations. Ru = ybq= 0.42(40 in)(83.2/144) = 9.7 lb/in To determine the reactions from the sloped loading, assume the plate spans from the top to bottom. lb. R 116 3. 33' 208 pof Rbot. = 231 lb. ft. 5 of 11 VI -D.42 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sample Calculation for Shield Design Sample Calculation for Shield Design Maximum Conservative Reaction is, [(9.7)(12)] + 231 = 347 lbs Check Anchor & Masonry I/2"0 A307 Anchor Bolt Allowable Shear per AISC 9th Edition, (Connection Section) (-) (1 0,000) = 1963 lbs>346 lbs O.K 4 Check horizontal shear in masonry. Locate bolt in middle of 12" CMU. Reference: ACI 530 Section 5.14.2.2 Area of bolt, Ab = 0.2 in2 edge distance, I e-12/2 -I/2 =5.75 <12 db =61 embedment, lb = 6" (chosen) allowable load in shear, B1= 1(350)" aiT.A)|Q124) where: Ab = Area ofAnchor bolt fm = Compressive Strength of Masonry f = Yield Strength ofAnchor Bolt y 6 of 11 Ennineerihq Principles and Practices of Retrofittina Flood-Prone.Residential Structures VI -0.43 January 1995 Chapter VI: GeneralDesign Practices Dry Floodproofing Sample Calculation for Shield Design for this anchor bolt pattern, Bv = min (350( (1500)( 0.2))'-),((0. 12) (0.2) (20ksi)) 1450,480 480 Ibs > 347 lbs CheckWalls Adjacent to Opening for Additional Loads : . _ _ _ _ _ _ _ i s 0 - . -t --$Df ' Chc l'( wde oS 7S f ma-sonry ,-:,s;tr;7>ip ,D Determine the maximum moment and shear (as simple span), at 5'-0" from top, MM, = 1872lb ft at bottom, VmK= 1404 lbs 7of 11 1% VI -D.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January1995 Sample Calculation for Shield Design Sample Calculation for Shield Design Note: for Seismic Zone 2, masonry cores on each side of opening are to be reinforced. Check Masonry Reference: ACI 530, Working Stress Design Assume: d 6" (middle) b Es = 12" (I1/2cores) 29x106 psi f m Em n = = 1500 psi 1.6x10 6 psi Table 5.5.1.3 ofACI Es/Em= 18 (modular ratio) 530 Fb = 1/3(1500 psi) = 500 psi (allowable compressive stress) Fs = 24,000 psi (allowable tensile stress) Try using 1 -#5 rebar each side of opening, A, = 0.31 in2, full height, p = steel ratio = As/bd = 0.31/((6)(12)) = 0.0043 f ~= M!A)d where: M = applied moment As = area of steel j = ratio of distance between centroid of flexural compressive forces and tensile forces = 1 -(K/3) K = -pn +(2pn + (pn)2 )1 2 n modularratio p = steel ratio 8 of 11 Enaineerina PrinciDlesand Practices of Retrofittina Flood-ProneResidential Structures VI -D.45 January 1995 ChapterVI: General Design Practices Dry Floodproofing Sample Calculation for Shield Design II K = -0.0043(18)+(2(0.0043)(18)+[(18)(0.0043)]2)1/2 = 0.3238 j = 1 -0.3238/3 = 0.8921 f5 = [(1872 lb ft)(12 in/ft)]/[(0.31)(0.8921)(6)] = 13,540 psi < 24,000 psi O.K. for tis example, fO = MI(1/2bjkd) where: M = appliedmoment b = width of section j = ratio of distance between centroid of flexural compressive forces and tensile forces = 1-(K/3) K = -pn+(2pn+(pn)2 )"' d = distance to centroid oftensile stresses from the maximum compressive stress n = modularratio p = steel ratio t = [(1872 lb ft)(l2 in/fl)]/ [1/2(12)(0.8921)(0.3238)(6)2i = 360 psi< 500 psi O.K. Walls adjacentto closure should have 1-#5 (middle) full height with matching dowel into footing, asaminimum. 9 of 11 VI -D.46 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sample Calculation for Shield Design Sample Calculation for Shield Design Check Shear in Masonry at Base V = 1404 lb Calculate shear stress, fV = V/(bjd) where: V = shear at point under construction b = width of section j = ratio of distance between centroid of flexural compressive forces and tensile forces = 1-(K/3) K = -pn+(2pn+ (pn)2)1"2 d = distance to centroid oftensile stresses from the maximum compressive stress n = modular ratio p = steel ratio for this example, f = 1404/ [(12)(0.8921)(6)] = 21.9 psi allowable shear stress, per ACI 530 Fv= (fm) = (1500)1/2= 38.7 psi >21.0 psi O.K. 10 of 11 Enaineerina Princioles and Practices of Retrofiffina Flood-Prone Residential Structures VI -D.47 January 1995 Chapter VI: General Design Practices Dry Floodproofing S, Sample Calculation for Shield Design Additional Considerations * If water level rises above the top ofthe opening, the closure may laterally load the lintel. In this case the lintel should be checked for biaxial bending. * Provide any additional code-required reinforcement around openings for the specific seismic zone. * Different methods of attachment may load the adj acent wall differently. * Confirm that gasket is suitable for depth/duration of flooding and selected construction materials. 11 of 11 VI -D.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Construction Considerations CONSTRUCTION CONSIDERATIONS FOR SEALANTS AND SHIELDS The use of sealants and shields may require careful attention to critical installation activities. When using shields and sealants, it isvitalthat * the sealant be applied in accordance withthe manufacturer's instructions; * wrapped systems are anchored properly and the surrounding soil recompacted; * shields are tightly installed with associated caulking or gaskets, utilizing the proper grade of materials and paying close attention to the anchoring details; and * multiple closures are accurately labeled and stored in an easily accessible space. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.49 January 1995 Chapter VI: General Design Practices ( Q< Dry Floodproofing DRAINAGE COLLECTION SYSTEMS The development ofdrainage collection systems is a critical component in the design of many dry floodproofing measures and may be utilized in concert with elevation, floodwall, and levee measures. These systems collect drainage and seepage from areas along, adjacent to, or inside the retrofitting measure and the sump pump installation, which transmits the collected drainage and seepage away from the building's foundation. Determination of the amount of surface water inflow and infiltration was presented in Chapter IV. This section presents the parameters that govern the design of these systems. Typical homes with basements are constructed on concrete footings upon which concrete or cinder block foundation walls are constructed. In some instances, the foundation walls are parged and covered with a waterproof coating, and/or perforated pipe underdrains are installed to carry water away from the exterior foundation walls (see Figure VI-D 18: Typical Residential Masonry Block Wall Construction). Thenthe excavations are backfilled and compacted. First Floor Slope Pway From "Ouse Basement Area Cement Mortar Parging with Asphalt Base Waterproofing Below Grade Concrete or Cinder Block Cove Area Concrete Basement Slab Gravel (may be reinforced with wire mesh) PC)rforated Pipe Footing Drain 111GraveS l Base (sometimes) Concrete Footing Figure VI-D 18: Typical Residential Masonry Block Wall Construction VI -D.50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Drainage Collection Systems However, in practice, this fill material is not and often cannot be compacted to a density equal to that of the undisturbed soils around the house. Because of the density difference, the fill material is capable of conducting and holding more water than the soil around it and frequently provides a storage area for the soil water. As flood levels rise around the structure, the combined water and soil pressure in the areas adjacent to the foundation increases to the point of cracking foundation walls and/or entering the basement through existing cracks to relieve the pressure. (See Figure VI-D 19: Common Faults Contributing to Seepage into Basements.) Settlement of Backfill Creating Water Collecting Depression First Floor (may occur even with good compaction) -Framing Slopes T-oward House (I Basement Area Parging Cracked, Does Not Extend To and Wrap Footing, or Parging Nonexistent 'a _W~ _ Surface and Subsurface Water Collects in Less Compact Fill Area Excavated and Backfilled ICrack in Wall During House Construction Hollow Core Block May Fill With Water Basement _ ~~~~~~~FloorSlab Joint Floor Drain- l Drain at or above Basement Floor Elevation, or Nonexistent Hydrostatic Pressure Forces Water through Wall, Floor Joints and Floor Openings (Floor Drain) Figure VI-DI9: Common Faults Contributing to Seepage into Basements Depending upon site-specific soil conditions, high water tables, and local drainage characteristics, slab-on-grade homes may experience similar seepage problems. In addition, elevating and! or dry floodproofing a slab-on-grade home may also necessitate the installation of drainage collection systems to counteract buoyancy and lateral hydrostatic forces. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.51 January 1995 Chapter VI: General Design Practices Dry Floodproofing Drainage collection systems consisting of perforated pipe drains are designed to collect this water and discharge it away from the structure, thereby relieving the pressure buildup againstthe foundation walls. Several types of drainage collection systems exist including french drains, exterior underdrains, and interior drains. FRENCH DRAINS French drains are used to help dewater saturated soil adjacent to a foundation. They are simply trenches filled with gravel, filter fabric, and sometimes plastic pipe. A typical french drain French rainsareenerallynotsection is shown in Figure VI-D20. The effectiveness offrench French drains are generally not dan scoeyte oteeitneoasial icag suitable for areas subject to drains is existence ofa suitable discharge requent inundation due to the point and the slope/depth ofthe trench. A suitable discharge lack of a gravity discharge point for the drain usually means an open stream, swale, ditch, or during a flood. However, they can slope to which the drain can be run. If such a discharge point is a be effective in keeping localized not available, a french drain is generally not feasible. drainage away from the foundation (providing there is no occurrenceof a significant flood). If feasible, the french drain should be dug to a sufficient depth to ensure the capture of soil water that might infiltrate the fill material inthe footing areaofthe basement. The slope ofthe trench should be such that good flow can be maintained between the gravel stones. This typically means a minimum slope of 1.0% or more. Roofing Felt or Filter Fabric to Prevent Infiltration of Fine Soil Topsoil / Particles in Drain Gravel 1_9IMinimum ,,,,,, {~~Typical Perforated Pipe in 3/4" to 1"Diameter Gravel Typca Figure VI-D20: Typical French Drain System VI -D.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Drainage Collection Systems Similar to the french drain, an exterior underdrain system with gravity discharge will not work during a flood. Therefore sump pump discharge with a backup energy source is the preferred alternative. EXTERIOR UNDERDRAIN SYSTEMS Exterior underdrain systems are generally the most reliable drainage collection system when combined with some type of foundation parging and waterproofing. The advantage of the exterior underdrain system is that it will remove water that would otherwise exert pressure against the foundation walls and floors. Underdrains are normally constructed of continuous perforated plastic pipe laid on a gravel filter bed, with drain holes facing up. The underdrains are placed along the building foundationjustbelowthe footing and carrywaterthat collects to a gravity discharge or sump pump for disposal into a public drainage system, natural drainage course, or ground surface (as permitted by local agencies). (See Figure VI-D2 1: Typical Exterior Underdrain System with Sump Pump and Figure VID22: Details of a Combination Underdrain and Foundation Waterproofing System.) Ennineprinn Princinles and Practices of F RetrofittinaFlood-ProneResidential Structures VI -D.53 January 1995 Chapter VI: General Design Practices Dry Floodproofing Exterior Footing Drain (perforated pipe in gravel bed) around Perimeter Plan View FloorSlab Foundation Walls Discha Line Sump Pump in Pit/ (one or more may be used) Floor /1 i Discharge Perforated Pipe (in gravel bed) Bel Line Floor Slab Along One or More Wal Side View Discharge Line Alternative Configuration: -(through wall at or above ground elevation and flood protection level) P Sump erforated Pit _~~~~~~~~~~~~~~~~~~~n pipe used) Sump Pit Basement Floor Slab Sump Pump Gravel Sump Pump Foundation System Perforated Pipe Connected Through Footing Below Floor Slab Figure VI-D2 1: Typical Exterior Underdrain System with Sump Pump Showing Two Alternative Configurations in the Side View VI-D.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Drainage Collection Systems Details of Underdrain and Foundation Waterproofing Asphalt base (or better) waterproofing application followed by layer of polyethylene sheeting 3/4"parging applied in two layers %" thick each Hollow \ -~~~~~~~Block Completely filled exterior cove \ wake / /1 Wall ~~~~~~Expansioin Filterfabric Joint sloped away from wall Basement s ~~~~~ ^ t v~~~~~~FloorSlab g3 roux a _ ~~~~~Mortar 1 / 9 ~~~~~~~Conc.Xa Drain below / Footing top of footing NV -1l,'" diametergravel / / ~4"min. 4" diameter perforated pipe Note: gravel may be extended to within 9" of finished grade FigureVI-D22: Details of a Combination Underdrain and Foundation Waterproofing System EngineeringPrinciples and Practices of Retrofitting Flood-ProneResidential Structures VI -D.55 January 1995 Chapter VI:General Design Practices 1n> m~. Dry Floodproofing INTERiOR DRAIN SYSTEM Interior drain systems are designed to relieve hydrostatic pressure from the exterior basement walls and floors and do not require tat the soil be excavated from around the exterior basement walls for installation. Sump pumps are perhaps the most familiar of all methods used to dewaterbasements. The sump is generally constructed so that its bottom is well below the base ofthe basement floor slab. Water in the areas adjacent to the basement walls and floor migrate toward the area of least pressure along the lines of least resistance, in this case toward and into the sump. It may be necessary to provide a more readily accessible path of least resistance for water that has collected in the fill material and around the house to follow. To achieve this, pipe segments are inserted and sometimes drilled through the basement wall and into the fill behind. These pipe segments are then connected to larger diameter pipes running along a gravel-filled trench or cove area into the basement floor and into one or more sumps. (See Figure VI-D23: Typical InteriorDrain Systems.) VI -D.56 Enaineerina Principles and Practices of Retrofittino Flood-Prone Residential Structures January 1995 Drainage Collection Systems Typical Interior DrainageSystems Underdrain System Wall Drainage System Below Basement Floor Slab Above Basement Floor Slab 1/2" Solid Plastic Holes Must/ or Be Drilled See Copper into Cinder ) Section Pipes Block Cores "B" Sump Cl I riuur ;:ilU Cl -L.L IA..- iviUSIRa-I | Pump Removed and Replaced Note:Water is collectedIn sumpandmust be pumpedto a suitable pointof discharge. Replacement Slab Around Perimeter of Basement Hyrdraulic Existing Ce)ment Basemerit in Cove Slab -Gravel 4" Perforated Pipe -X Section "A" Section "B" Note:Holesmust be drilled Intoblockcoresat 8' Intervalsascloseto floor as possible. This methodmust be considered an Inexpensive alternativeto a below slab system and accordinglyhascertainshortcomings:pipe is visible;will not drainfromwellbelow floor elevation;problemsassociatedwithdampness mayremain;hydrostaticpressurebelowfloor slabmay not be sufficientlyrelieved. I Figure VI-D23: Typical Interior Drain Systems VI-U..I x ,. , rag Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -Lv.01 January 1995 ChapterVI: General Design Practices Dry Floodproofing SUMP PUMPS TYPES OF SUMP PUMPS Two types ofsump pumps commonly used are the submersible and the pedestal. The submersible type has a watertight motor tat is directly connected to te pump casing. It is installed at the bottom ofthe sump. The pedestal sump pump uses an open motor supportedon a pipe columnwith the pump at its base. A long shaft inside the column connects the motor to the pump impeller. Figure VI-D24 depicts both ofthese pumps. Sub mersible pumps are preferred because they will continue to operate if the flood level exceeds the height of the pump. Three Wire GroundedPower Cord Control Switch\ Three Wire GroundedPowerCord Float Rod Control Switch I Chamber Motor K Housing Tube1 Float Column Float-/ Pump / Case]j Impeller \-Screen / \ZOUnn1 Pump Case LImpeller t-Screen Typical Submersible Pump Typical Pedestal Pump FigureVI-D24: Types of Sump Pumps VI-D.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sump Pumps In selecting a sumppump for use inresidential floodproofing, , the designer should consider the advantages of each pump type and make a selection based on requirements determined from investigation ofthe residence. Considerations include pump Batterypoweredmarine-typebilge capacity (gallons per minute or gallons per hour), pump head *pumps are an alternative to sump pumps/electricalgenerator (vertical height that the water is lifted), and electrical power pminstallations. required (residential electrical power is usually 120/240 volts AC, single phase). Sump pump motors generally range in size from 1/6horsepowerto 1/2horsepowerdesigned to operate on either 120 or 240 volts. Infiltration vs. Inundation The capacities of sump pumps used in residential applications are limited. In floodproofing, sump pumps are used to prevent accumulations of water within te residence. In conjunction with other floodproofing methods, sump pumps can be used to protect areas around heating equipment, water heaters, or other appliances from floodwaters. Sump pumps are useful to protect against infiltration of floodwaters through cracks and small openings. Inthe event that there are large openings, or that the structure is totally inundated, the pumping capacity of sump pumps is often exceeded, but they are useful for controlled dewatering after floodwaters slowly recede (if submersible pumps are used). COORDINATION WITH OTHER FLOODPROOFING METHODS Design and installation of a sump pump should be coordinated with other floodproofing methods such as sealants and shields, protection of utility systems (furnaces, water heaters, etc.) and emergency power. Pnrninarinn Prinnini an.ndPractirce ofRptrofittina Flood-Prone Residential Structures VI-D.59 January 1995 # Chapter VI: General Design Practices DryFloodproofing FIELD INVESTIGATION Detailed information must be obtained about the existing structure to make decisions and calculations concerning the feasibility of using a sump pump. Use the Building/Building System Data Sheets (Figures VL-3and VI-4) as a guide to record infonnation about the residence. Items that the designer may require are covered on the sump pump field investigation worksheet, (Figure VI-D25). VI -D.60 Enaineerina PrinciDles and Practices of Retrofittinr FIoonr-Prnn ResirdentialIQtriintimrao January 1995 Sump Pumps Owner Name: Prepared By: Address: Date: Property Location: Sump Pump Field Investigation Worksheet El Document physical location and characteristics of electrical system on sketch plan below. El Determine base flood elevation: El Check with local building official's office for version of National Electrical Code (NEC) NFPA70, and local Electrical Code requirements: D Check with local building official's office for established regulations concerning flooded electrical equipment: El Check with the regulatory agencies to determine which state and local codes and regulations regarding the design and installation of plumbing systems may apply to the installation of a sump pump: El Determine location and condition of any existing drainage collection systems, including sump pits and pumps. El Does residence have subterranean areas such as a basement? ____Yes No El Is there a sump pump installed presently? _Yes -No: If so: El Record nameplate data from pump: capacity( motor horsepower, voltage, and manufacturer's GPH or GPM @FT name and model number. HEAD), EII Sketch plan of basement indicating location of sump, heating and cooling equipment, water heaters, and floor drains. E1 How high above floor is receptacle outlet serving cord and plug connected to sump pumps? Figure VI-D25: Sump Pump Field Investigation Worksheet Engineering Principles -rndPractices of Retrofitting Flood-Prone Residential Structures Vi -D.61 January 1995 ChapterVI: General Design Practices Dry Floodproofing I Once this data is collected, the designer should answer the questions below to develop a preliminary concept for the installation of a sump pump. D If there is no sump pump and one is needed, note potential location for a sump and tentative location for pump discharge piping on above sketch plan. D Is there an electrical outlet nearby? Yes No D7 Does electrical panel have capacity to accommodate additional GFI circuit if necessary? __Yes -No El If other floodproofing measures are to be considered, such as placing a flood barrier around heating equipment or other appliances, is the existing sump pump in an appropriate location? Yes _ No Does another sump and sump pump need to be provided? Yes -No D Select emergency branch circuit routing from sump pump to emergency panel. Note on above sketch plan. D Is sump pump branch circuit located above flood protection elevation and is it a GFI circuit? ___Yes No ELI Locate sump pump disconnect or outlet location near sump pump location above FPE. Once these questions have been answered the designer can confirm sump pump installation applicability through: LII Verify constraints because of applicable codes and regulation. [I] Sump pump needed? -Yes _ No L Is sump pump required by code? ____Yes No D Code constraints known? ----Yes -No D Proceed to design? Yes No C: Confirmthat wiring can be routed exposed in unfinished areas and concealed in finished areas. ___Yes No D Confirmthat panel has enough power to support sump pump addition. -Yes -No I . Figure VI-D25: SumpPump Field Investigation Worksheet (continued) VI- D.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sump Pumps DESIGN The design of sump pump applications follows the procedure outlined in the flow chart in Figure VI-D26: Sump Pump Design Process. Sump Pump Design Process Determine Rate of Drainage Determine Location for Sump Determine Location for Discharge Select Pump Size Determine Adequate Sump Capacity and Size Select Discharge Piping Route Size Electrical Components Prepare Details and Specifications Figure VI-D26: Sump Pump Design Process Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -D.63 January1995 Chapter VI: General Design Practices < Y~ DryFloodproofing Step 1: Determine rate of drainage. (Covered previously in Chapter IV.) Step 2: Determine location for sump. Refer to Figure VI-D27 for typical sump pump installation. Considerthe following in locating the sump. * Isthere adequateroom for the sump? * Are there sub-floor conditions (i.e., structural footings) that would interfere with sump installation? * If penetration of floor is not recommended, consider using a submersible pump design for use on any flat surface. * Are other floodproofing measures being considered, such as placing a flood barrier around heating equipment or plumbing appliances? If so, locate sump or provide piping to sump to keep protected area dewatered. Make preliminary sketch showing location of sump pump, discharge piping, and location of electrical receptacle for pump. * Coordinate sump location with design of drainage collection system. VI -D.64 Enaineerina PrinciDlesand Practices of Retrofittino Flood-Prone Residential Strictures -in sor _ ----t*-_ -Ju 1 99 January 1 995 Sump Pumps Typical Sump Detail (No Scale) Discharge to Outdoor or Other_ Drainage Systemr Discharge To Battery or As Allowed \CPipe and Back Up Power Unit ProtectionLevel Check | Sm oe Sump Varies Submersible (1-4 Typical)-~ar, Sump Pump Varies (18"-36" Typical) Figure VI-D27: Typical Sump Detail Step 3: Determine location fordischarge. Check with local authorities having jurisdiction about the dischargeof clearwaterwastes. Inmost jurisdictions, itisnot acceptable to connect to a sanitary drainage system, nor may it be desirable since, in a floodsituation,it may backup. If allowable, the desirable location for the discharge is a point above the BFE at some distance away from the residence. The discharge point should be far enough away from the building that water does not infiltrate back into the building. From the information obtained during the field investigation, tentatively lay out the route ofthe dischargepipingand locatethepoint of discharge. Fnni D;nn imrinec onri Drotii'.c of RPtrcfittinnFloodrr-ProneResidential Structures VI -D.65 Jaluyll 199t 5I lu r -%-IW lu I c January 1 995 ChapterVI: General Design Practices Dry Floodproofing Step 4: Make selection ofpump. Sump pumps for residential use generally have motors inthe range of 1/6 to 3/4 horsepower and pumping capacities from 8 to 60 gallons per minute. In selecting a pump, the designer needs the following information: Estimate of the quantity of floodwater that will infiltrate into the space per unit of time (GPM or GPH). The total dynamic head for the sump discharge. This equals the vertical distance from the pump to the point of discharge plus the frictional resistance to flow through the piping and fittings. Use the preliminary sketch and field investigation information developed earlier to determine these parameters. The total discharge head, TH, is computed as follows: TH=D ~ + h~ig | = 111 TH = Ds +h* h~~f 1 9 pipe+ f-fittings where: TH is the total head in feet; D is the difference in elevation between the bottom ofthe sump and the point of discharge, in feet; hflpipe is the head loss due to pipe friction, in feet; and hr fittings is the head loss through the fittings, in feet Fonnula VI-D 1: Total Discharge Head VI-D.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Sump Pumps The head loss due to pipe friction can be obtained from hydraulic engineering data books and is dependent on the pipe material and pipe length. The head loss due to pipe fittings is calculated as follows: N_ hffiuings = Kp (V 2/2g) where: hr fiings is the head loss through pipe fittings, in feet; K P is the resistance coefficient ofthe pipe fitting(s), taken from hydraulic engineering data books; V is the velocity of flowthrough the pipe, in feet per second, taken from hydraulic engineering data books; and g is weight of gravity, 32.2 pounds per second squared. Formula VI-D2: Head Loss Due to Pipe Fittings The following example illustrates the use ofthese equations to determine the total head requirements for a sump pump installation. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.67 January 1995 Chapter VI: General Design Practices Dry Floodproofing Sample Calculation for Sump Pump f GIVEN: Ds = 10 feet; flow assumed to be 20 gpm; 1.5 inch steel discharge pipe length of 30 feet includes one elbow, one gate valve and one check valve. SOLUTION: From Hydraulic Engineering Data Books, resistance to flow in a 1.5-inch steel pipe is 2.92 feet per 100feet ofpipe; hfpipe= 2.92 (30/1 00) = 0.876 feet resistance coefficients for fittings are K (elbow) = 0.63; K (gate valve) = 0.15; K (check valve) = 2. 1; K (sudden enlargementoutlet)= 1.0 K=0.63 +0.15+2.1 + 1.0 =3.88 velocity converted from gallons per minute to feet per second = Vfps4 Q 450 A pipe fit3 gal Dry Floodproofing BACKWATER VALVES Backwater valves can help prevent backflow through the sanitary sewer and/or drainage systems into the house. '00-40 They should be considered for sanitary sewer drainage Dependingupon the hydrostatic systems that have fixtures below the FPE. In some in- pressurein the sewer system, a stances, combined sewers (sanitary and storm) present the simple wood plug can be used to greatest need for backwater valves because they can prevent close floor drains. both a health and flooding hazard. Backwater valves are not foolproof: their effectiveness can be reduced because of fouling ofthe internal mechanism by soil or debris. Periodic maintenance is required. The backwater valve is similar to a check valve used in domes tic water systems (Figure VI-D28). It has an internal hinged plate that opens in the nonnal direction of flow. If flow is reversed ("backflow"), the hingedplate closes overthe inlet to the valve. The valve generally has a cast-iron body with a removable cover for access and corrosion-resistant internal parts. The valves are available innominal sizes from two to eight inches in diameter. As an added feature, some manufacturers include a shear gate mechanism that can be manually operated to close the drain line when backwater conditions exist. The valve would remain open during normal use. A second type of backwater valve is a ball float check valve (Figure VI-D29) that can be installed on the bottom of outlet floor drains to prevent water from flowing up through the drain. This type of valve is oflen built into floor drains or traps in newer construction. Advanced backwater valve systems have ejector pump attachments that are used to pump sewage around the backflow valve, forcing it into the sewer system during times of flooding. This system is usefull in maintaining normal operation of sanitary anddrainagesystemcomponents during a flood. VI-D.72 EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Backwater Valves II ,~~~~~~~~~~~ I, ~Backwater Valve -Handwheel .A : 'Operator :_Optional Optional- Manhole Check Critical Valve Part | Normal Flow IS Direction ------------------L -Shear-Gate Figure VI-D28: Backwater Valve Figure VI-D29: Floor Drain With Ball Float Check Valve Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI- D.73 January 1995 ChapterVI: General Design Practices Dry Floodproofing FIELD INVESTIGATION Detailed information must be obtained about the existing "a structure to make decisions and calculations concerning the feasibility of using a backwater valve. Use the Building/ Alternatives to backwate Drvalves Building System Data Sheets as a guide to record informainclude overhead sewers and tion about the residence. Once this data is collected, the standpipes. Their use sl ould be designer should answer the questions below to develop a evaluated carefilly. preliminary concept for the installation of a backflow valve. DESIGN The designer should follow the process illustrated in Figure VI-D30: Backwater Valve Selection, to design, select, and specify the backflow valve. Backf low Valve Selection Determine Relationship of Drains to Flood Protection Elevation Confirm Regulations Concerning Backwater Valves I I Determine Layout of Drains that Serve Impacted Fixtures I I Determine Pipe Sizes on Impacted Drains I Type, Size and Location for Valves; | De~Dvelop Figure VI-D30: Backwater Valve Selection VI- D.74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Backwater Valves Owner Name: Prepared By: Address: Date: Property Location: Backwater Valve Field Investigation Worksheet D Does residence have plumbing fixtures or floor drains below FPE: -Yes -No D Is building drainage system equipped with backwater valves, or do floor drains have backwater device? -Yes No: If so, locate on a floor plan sketch of the residence. D If there are no backwater valves and they are needed, consider the following in selecting a location for their installation. D Can adequate clearance be maintained to remove access cover and service valve? Yes No D Are there any codes that regulate or restrict installation of such valves? -___Yes No; If yes, explain. D Tentatively locate on sketch box where backwater valves might be installed. CD Proceed To Design? _ Yes __No Figure VI-D3 1: Backwater Valve Field Investigation Worksheet Engineering Principles and Practices of Retrofittina Flood-ProneResidential Structures VI -D.75 January 1995 Chapter VI: General Design Practices Y 9< ~ Dry Floodproofing The elements of this process include: Step 1: Determine relationship of drains to FPE. If any drain or pipe fixtures are located below the FPE, backwater valves should be installed. If all drains and fixtures are located above the FPE, backwater valves are not necessary. Step 2: Determine regulations concerning backwater valves. Based upon information collected during the field investigation, confirm the allowability of and the regulations governing the installation of backflow valves. Step 3: Determine layout of drains that serve the impacted fixtures. Make a floor plan sketch showing location of all plumbing fixtures and appliances, floor drains, and drain piping that is below the FPE. Step 4: Determine pipe sizes on impacted drains. Obtain from field investigation the size of drainage lines below the FPE. Step 5: Determine type, size, and location for backwater valves. Determine type, size, and location of backwater valves required, paying considerable attention to any special conditions related to installation. Factors to be considered include: Clearance for access and maintenance VI -D.76 Enaineering Principles and Practices of Retrofittina Flood-ProneResidential Structures January 1995 Backwater Valves * Cutting and patching of concrete floors * Indicate on floor plan sketch the tentative location(s) ofthe backwater valve(s). At this point the designer should confinr the preliminary design with the homeowner, discussing the following items: If possible, backwater valves * Verify that proposed locations of backwater valves are should be located outside a feasible. structure so as to minimize damage should the pressurized line fail. * Verify existing conditions at location of proposed backwater valve installation. Confirm the size and location of needed backwater valves. * Confirm special considerations regarding existing conditions affecting design and installation of backwater valves. Step 6: Prepare details and specifications. The final plans and specifications should include the following items: * Floor plan with location of backwater valves * Details, notes, and schedules -Backwater valve detail -Wall, floor, and wall penetration details Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.77 -January 1995 Chapter VI: General Design Practices Dry Floodproofing -Installation notes -Equipment notes (or schedule) * Prepare specificationsgoverning the installation of: -Pipe and fittings -Insulation -Hangers and supports -Valves * Coordinate plans with work of others on additional floodproofing measures that may be proposed at the same residence. VI -D.78 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January1995 Emergency Power EMERGENCY POWER Emergency power equipment can be applied to residential applications if the proper guidelines are observed. First, it is not feasible to apply emergency power equipment to the operation of a whole house with electric resistance heat, heat pumps, air conditioning equipment, electric water heater, electric cooking equipment, or sump pump(s). These large loads would require very expensive emergency power equipment that would have considerable operating costs. However, small, economical, residential portable generators or battery backup units can be successfully installed to operate selected, critical electrical devices or equipment from the limited power source. A list of appliances or equipment that a homeowner might choose to operate is shown in Table VI-Dl. It is important to note that all of these appliances would most likely not be operated at the same time. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.79 January1 995 X A~ Chapter VI: General Design Practices Q v Dry Floodproofing Table VI-D Essential Equipment/Appliances to Operate from Emergency Power Source Critical Items include: * Floodwatersump pump -typically 113to 1/2 hp 120 volt single phase. * Domestic sewage pump -typically 3/4 hp to 1 hp 120 volt single phase. Non-critical items include: * Refrigerator -350 watts to 615 watts. * Freezer -341 watts to 440 watts. * Gas or oil furnace -1,7 hp burner, 1/3 hp to 1/2 hp blower motor. * Some lighting or a light circuit -limit to about 400 watts. * A receptacle or a receptacle circuit -limit to about 600 watts. Several sources of technical information are available to assist in the design of emergencyresidential generator set installations. * Some manufacturers provide application manuals and sizing forms to select small gasoline-powered, natural or liquid petroleum gas, or battery sets. * Other manufacturers even offer software to size the small generator/battery sets. * Another good source is the supplier of the standby generatorlbattery set. These have additional application data for sizing the unit to suit the anticipated load. * The manufacturer of the set will provide a wattage and volt-ampere rating for each size at a particular voltage rating. Selection of a generator/battery set is a matter of matching the unit capacity to the anticipated maximum load. The chief VI -D.80 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Emergency Power complication in sizing the generator/battery set is the starting characteristics of the electric motors in the pumps and appliances to be served. FIELD INVESTIGATION Detailed informationmust be obtained about the existing structure to make decisions and calculations concerning the feasibility of using an emergency generator or battery backup unit. Use the Building/Building Systems Data Sheets (Figures VI-3 and VI-4 located in the beginning of Chapter VI) as a guide to record information about the residence. Among the activities the designer may pursue are: * Examine the routing and condition of the existing building electrical system, noting potential locations for emergency power components (above the FPE and away from combustible materials). * Determine utility or power company service entrance location and routing. * Determine utility constraint data. * Record these items and locations on an electrical site plan/combination floor plan sketches. * Confirm space for cable routing between main panel, emergency panel, transfer switch, and proposed generator/ battery set. * Examine existing panel branch circuit breakers and select circuits to be relocated to emergency panel. * Confirm utility regulations on emergency power equipment with local power company. Ennineerinn PrinrinIlA and PrartircAs of FRetrofittino Flood-Prone Residential Structures VI -D.81 January1995 ChapterVI: General Design Practices Dry Floodproofing DESIGN The design of emergency power provisions is a straightforward process that is illustrated in Figure VI-D32. The steps include: Emergency Power Design Determine Loads to Operate on Generator or Batterv Set Identify Start and Run Wattages Calculate Maximum and Minimum KW for Above Loads I |ISelect Generator/Battery Set SizeI| E Sele~ctTransfeSwthiz Transfer Switch Select Emergency Panel Size Manual Transfer Switch Design Wire Conductor and Raceway Ground SLstem Prepare Construction Detail Plan I and Specifications Figure VI-D32: Emergency Power Design Process VI -D.82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Emergency Power Step 1: Determine loads to operate on generator set. Table VI-D2 presents typical electrical appliance loads for Since most power outages are some home equipment. The designer should work with the temporary and relatively short owner to select only those pumps/appliances that must be lived, a battery backup source for run by emergency power and confirm the estimated appli sump pumps (only) may be the ance and motor loads. simplest solution for a homeowner. However, as the duration of the power outage Step 2: Identify start and run wattages. increases, the suitability of battery backup systems decreases. Start and run wattages for the appliance loads selected by Generator sets are a more secure source of power in these situa-the homeowner can be obtained from Table VI-D2, Typical tions, especially for those resi-Electric Appliance Loads. dents who need/desire power to operate medical equipment or standard household appliances Step 3: Calculate maximum and minimum KW for operat during power outages. Battery ing loads. systems used in conjunction with emergency generators can provide service during a limited period if Based upon the loads determined in Step 1, the designer the owner is not home when the should develop the range of minimum and maximum watt- power goes out. ages for the desired applications. Table VI-D2, Typical Electric Appliance Loads, can be used to estimate these minimum and maximum loads. TableVI-D2 Typical Electrical Appliance Loads HomeEquipment Typical Wattage Start Wattage Critical items: Limited lights (safety) 400 400 Sewage pump (3/4 hp to 1 hp) 1000 4000 Sump pump (1/3 hp to 1/2 hp) 333 2300 Water pump 800-2500 800-10000 Non-critical items: Refrigerator 400 -800 1600 Freezer 600 -1000 2400 Furnace blower 400 -600 1600 Furnace oil burner 300 1200 Furnace stoker 400 1600 Limited receptacles 600 600 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -D.83 January1995 Chapter VI: General Design Practices Dry Floodproofing Step 4: Select generator/battery unit size: At' Size the generator/battery unit set from load information ob- Emergency power equipment tained in Step 1. Generator/battery unit set sizing is based upon should be located above the flood the approximation that motor starting requirements are three to protection level. four times the nameplate wattage rating; thus, generator sets/ battery units should be sized to handle four times the running watts of the expected appliance loads. Small generators/battery unit sets are usually rated in watts. Two ratings are often listed-a continuous rating for normal operation and a higher rating to allow for power surges. Match higher surge ratings with the starting wattage. Generator sets can be loaded manually with individual loads coming on line in a particular sequence, or the loads can be transferred automatically with all devices trying to start at one time. This is illustrated by the following examples. Table VI-D3 Example of Maximum Generator Sizing Procedure RUNNING LOAD STARTING LOAD SEWAGE PUMP 1000 4000 FURNACE 300+400=700 1200 + 1600 = 2800 SUMP PUMP 333 2300 REFRIGERATOR 400 1600 FREEZER 600 2400 RECEPTACLES 600 600 LIGHTS 400 400 TOTALS 4033 WATTS 14100 WATTS Select a generator with a continuous rating that is at least as large as the total wattage to start all loads at once. 14KW appears to be the minimum size to start all motors at once. VI- D.84 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Emergency Power TableVI-D4 Example Step Sequence Manual Start -Minimum Generator Sizing Starting Running Loads Loads Sewage Pump Step 1 4000 Furnace Step 2 2800 + 1000 =3800 Sump Pump Step 3 2300 + 700 + 1000 = 4000 Refrigerator Step 4 1600 + 333 + 700 + 1000 = 3633 Freezer Step 5 2400 + 400 + 333 + 700 + 1000 = 4833 Receptacles Step 6 600 + 600 + 400 + 333 + 700 + 1000 = 3633 Lights Step 7 400 + 600 + 600 + 400 + 333 + 700 + 1000 = 4033 Largest Load 4,833 Watts; Thus 5KW Generator Set is minimum size. For each step or appliance load, add the running wattage of items already operating to the starting wattage of the items being started in that step. Select the largest wattage value out of all steps. Compare maximum wattage with continuous wattage rating of the generator. At this point, the designer has sufficient information to present preliminary equipment recommendations to the homeowner, prior to the design oftransfer switches, emergency panels, wiring, and other miscellaneous items. Among the issues the designer should confirm with the homeowner are: * The essential power loads proposed for the generator/ battery set. Discuss any other essential loads pertaining to life or property safety. * Generator/battery set siting and proposed location. This should be discussed in light of unit weight, portage, storage, and handling methods. * Provisions for fuel storage and fuel storage safety. FnninAerinnPrinrinins and Practices of Retrofittina Flood-Prone Residential Structures VI -D.85 January1995 Chapter VI: General Design Practices Dry Floodproofing The designer should also: * Educate the homeowner on battery operating time and/or generator operating time vs. fuel tank capacity. * Present initial generator/battery set cost and future operating costs. * Discuss requirements for having equipment located above FPE. * Discuss generator heat radiation and exhaust precautions to prevent carbon monoxide poisoning. Step 5: Selectiontransfer switch size. Transfer switches are designed to transfer emergency loads from the main house system to the generator/battery system in the event of a power failure. After power has been restored, the transfer switch is used to transfer power from the generator/battery set to the house system. Transfer switches can be manual or automatic. It is important to check with local code officials regarding requirements for how transfer switches are set up. Manual Transfer Switches generally have the following characteristics: * Double pole, double throw, nonfrsible, safety switch, general duty with factory installed solid neutral, and ground bus. Double pole, double throw transfer switches are typically required to prevent accidentally feeding power back into the utility lines to workers servicing the line. This switch also protects the generator set from damage when the power is restored. * Transfer switches are available with NEMA 1 enclosures for indoor mounting and NEMA 3R enclosures for outdoor locations. VI -D.86 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Emergency Power * The voltage rating oftransfer switches is typically 250 volts. * Available sizes are 30 amp, 60 amp, 100 amp, and 200 amp. The designer should consider the following items when selectinga manual transfer switch: * Coordinate amperage to match emergency panel rating, continuous current rating of branch circuits, genset overcurrent protection, and panel branch feeder circuit breaker size. * Fusible manual transfer switches are required as service entrance equipment and are required if the panel circuit breaker size does not correspond to the emergency panel size and generator/battery set circuit breaker size. * Several manufacturer models are not load break rated and require load shedding before transfer operation. These switches must be used for isolation only. They do not have quick make-quick break operation. * Some transfer switches are padlockable in the "off' position. * Switches should have door interlocks to prevent the door from opening with the handle in the "on" position. * Avoid locatingthe transfer switch at a meter or service entrance outdoor location. Switches are not service entrance rated unless they are fusible, and with this scenario the total house load is transferred to the genset. This method requires a much larger switch and cannot be taken out of service without de-energizing the entire dwelling. Engineering Principles and Practices ofRetrofitting Flood-Prone Residential Structures VI -D.87 January1 995 Chapter VI: General Design Practices Dry Floodproofing Automatic transfer switches are much more expensive than manual transfer switches and require an electrical start option for the generator/battery set. These switches are usually not cost effective forhomeowner generator/battery set installations but may, in certain applications involving life safety issues, wanrant the added expense. Automatic transfer switches automatically start the generator! battery set upon loss of regular power and transfer the emergency load to the generator/battery source. After power has been restored for some time, the transfer switch automatically transfers back to normal power source. The generator set continues to run for some time unloaded until the set has cooled down, then it shuts off. The designer should contact the manufacturers for specific applications data for these automatic transfer switch devices. Step 6: Select emergency panel size. Equipment and appliances that need to be powered by a generator/battery set are typically wired in an emergency panel box. The design of the emergency panel box should be conducted with the following considerations in mind: * Select branch circuit loads for emergency operation. * Size branch circuit over current devices in emergency panel to protect equipment and conductor feeding equipment. Appliance circuits and motor loads should be sized in accordance with NEC requirements. d Size panel bus based upon NEC requirements and on continuous rating at 125% calculated load for items that could operate over three hours. o Verify panel box size vs. number and size of circuit breakers. VI -D.88 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Emergency Power * See Tables VI-D5 and VI-D6 for minimum panel bus sizes and emergency panel specification criteria. TableVI-D6 Emergency Panel Specification Criteria * Load center type residential panel * Main lug * Indoor NEMA 1 enclosure above flood protection level with isolated neutral for sub panel application * Same short circuit current rating as main panel with ground bar kit * Pole spaces as required for appliance and motor circuit breakers At this point, the designer should confirm several items with the homeowner including: emergencypanel location above flood protection levele * transfer switch location above flood protection level * no load transfer switch operation Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-D.89 January1995 Chapter VI: General Design Practices Dry Floodproofing Step 7: Design wire conductor and raceway ground system. Select route for wiring between panel, transfer switch, and generator set and specific wiring materials in accordance with local electric codes or NEC. Operation and Maintenance Issues: The following instructions should be provided to the homeowner with generator equipment. For manual start generators, operating procedures include: 1. Turn offor disconnect all electrical equipment including essential equipment in emergency panel. CAUTION: Make sure solid state appliances remain off while standby power is operating. 2. Connect generator to receptacle. 3. Place transfer switch in generator position. 4. Start generator and bring it up to proper speed (1800 rpm or 3600 rpm). Check generator volt meter; it should read 11 5-125 volts; the frequency meter should read 60 Hz plus or minus three hertz. 5 . Start the motors and equipment individually, letting the genset return to normal engine speed after each load has been applied. The load should be applied in the sequence used to determine the genset size and generally with the CAUTION:if problemsoccur, largest motor load applied first. If the generator cuts out, turn off existing panel circuit turn offall the electrical equipment and restart. breaker feeding the transfer switch before investigating 6. Checkthevoltmeterfrequently. If itfallsbelow200 volts problemswith faultyconnections for 240-volt equipment or 100 volt for 120-volt equipment, or wiring, reduce the load by turning off some equipment. VI-D.90 Engineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Emergency Power 7. When normal power has been restored, turn off all the electrical equipment slowly, one load at a time. Turn offall emergency load, place transfer switch in normal load position, and turn electrical equipment back on. 8. Turn off genset circuit breaker. However, allow genset approximately five minutes to run for cool-down. Then turn off generator engine. Return generator to storage location. For manual start generators, maintenance procedures include: 1. Operate generator at about 50% load monthly or bimonthly to ensure reliability. 2. Check for fuel leaks. 3. Change engine oil per manufacturer's requirements. 4. Replace or use the fuel supply about every 30 to 45 days to prevent moisture condensation in the tank and fuel breakdown. Gasoline additives can keep gasoline-powered generator fuel from breaking down. 5. Keep tank full. 6. Replace air filter element per manufacturer's requirements. CONSTRUCTION All wiring shallbe installedby licensed electricians to meet NEC requirements, local electrical regulations, and requirements of the local power company. Bond ground from generator emergency panel through transfer switch back to main service panel. =nningarinn Prinpinineand Practices of Retrnfittinn Flood-Prone Residential Structures VI -D.91 January19' 95 l._*v -- Januaryl 995 Wet Floodproofing Table of Contents Protection of the Structure ........................................................... VI -W.2 Foundations ........................................................... VI -W.2 Cavity Walls ........................................................... VI -W.2 Solid Walls ........................................................... VI -W.3 Design of Openings in Foundation Walls forIntentional Flooding of Enclosed Areas Below the FPE ........................................................... VI -W.4 Use of Flood-Resistant Materials ........................................................... VI -W.6 Building Operation and Maintenance Procedures and Emergency Preparedness Plans ......VI -W.7 Flood Warning System ........................................................... VI -W.7 Inspection and Maintenance Plan ........................... ................................ VI -W.7 Flood EmergencyOperation Plan........................................................... VI -W.8 Protection of ServiceEquipment ............................................................ VI -W.9 Relocation........................................................... VI -W.9 Elevation............................................................ VI -W.9 In-Place Protection ........................................................... VI -W.10 - Field Investigation............................................................ VI W.11 Design Overview ........................................................... VI -W. 14 Mechanical Systems ............................................................ VI -W.15 Piping Systems ........................................................... VI -W. 16 Tanks........................................................... VI-W.16 Homeowner Coordination ............................................................ VI -W.17 For Shielding Measures ........................................................... VI-W.17 For Relocation Measures ............................................................ VI -W.17 nnin,...nni nlPri Drn,,+ipqa o~fPatrfffttinn Flond-Prnne Reaidential Structures VI -W.i January 1995 Developing Design Details and Specifications ........... ..................... Verify Design with Homeowner ................................ Prepare Construction Documents ................................ Electrical Systems ................................ Central Heating System Alternatives ......................... ................................................ Gravity Furnaces .VI Forced Warm Air Furnaces .VI Hot Water Heating Boilers .VI Heat Pump Compressors .VI Central Cooling System .VI IndoorUnits .VI OutdoorUnits .VI Ductwork .VI Unitary A/C Systems .VI Ductwork Systems .VI Piping Systems .VI Fuel Supply/Storage Applications .VI In-Space Heating Equipment .VI Room Heaters and Wall Furnaces .VI Oil/Kerosene Heaters .VI Electric Heaters .VI Water Systems .VI Drinking Water Wells .VI On-Site Portion of Water Systems .............................. Sewer Systems ............................... On-Site Portion of Sewer Systems .............................. SepticTanks .............................. Telephone Systems .............................. Cable TV Systems .............................. Construction .............................. Electrical..... Mechanical ..... VI -W. 18 VI -W. 18 VI -W.18 VI -W.19 VI -W.22 -W.23 -W.24 -W.25 -W.26 -W.26 -W.26 -W.27 -W.27 -W.27 -W.27 -W.29 -W.30 -W.3 1 0 -W.3 1 -W.3 1 -W.32 -W.32 -W.32 VI -W.33 VI -W.34 VI -W.34 VI -W.35 VI -W.37 VI -W.3 8 VI -W.39 VI -W.39 VI -W.40 VI -W.ii Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 - WET FLOODPROOFING Wet floodproofing can be defined as permanent or contingent measures applied to a structure and/or its contents that prevent or provide resistance to damage from flooding by allowing floodwaters to enter the structure. The basic characteristic that distinguishes wet floodproofing from dry floodproofing is that it allows internal flooding of a structure as opposed to providing essentially watertight protection. Flooding of a structure's interior is intended to counteract hydrostatic pressure on the walls, surfaces, and supports of the structure by equalizing interior and exterior water levels during a flood. Inundation also reduces the danger of buoyancy from hydrostatic uplift forces. Such measures may require alteration of a structure's design and construc tion, use of flood-resistant materials, adjustment of building operation and maintenance procedures, relocation and treatment of equipment and contents, and emergency prepared ness for actions that require human intervention. This section examines: * protection of the structure; * design of openings for intentional flooding of enclosed areas below the FPE; * use of flood-resistant materials; * adjustment of building operation and maintenance procedures; o the need for emergency preparedness for actions that require human intervention; and o design of protection for the structure and its contents including utility systems and appliances. Wet floodproofmg is appropriate for basements, garages, and enclosedareas below the flood protection level. Fngineerinn Principles and Practices of Retrofittina Flood-Prone Residential Structures VI -W.1 January 1995 ChapterVI: General Design Practices $Q\ŽNWet Floodproofing PROTECTION OF THE STRUCTURE 6 The NFIP allows wet flood- proofing only in limited situa tions. The most common application is with pre-FIRM structures not subject to substan tial damage and/or substantial improvement criteria. Structures in the pre-FIRM category can utilize any retrofitting method. However, for new structures or those that have been substantially damaged or are being substan tially improved, application of wet floodproofing techniques is limited to the following situa tions: * Enclosed areas below the BFE thatare used solely for parking, buildingaccess, or limited storage. These areas must be designed to allow for the automatic entry and exit of floodwaters through the use of openings, and be constructed of flood- resistant materials. * Attached Garages. A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry and exit of floodwaters. Openings are required in the exterior walls of the garage or in the garage doors. In addition, the areas below the BFE must be constructed with flood-resistant materials. * FEMA has advised communities that variances to allow (continued on next page) As with dry floodproofing techniques, developing a wet floodproofing strategy requires site-specific evaluationsthat may necessitate the services of a design professional. The potential for failure of various structural components (foundations, cavity walls, and solid walls) subjected to inundation is a major cause of structural damage. FOUNDATIONS The ability of floodwater to adversely affect the integrity of structure foundations by eroding supporting soil, scouring foundation material, and undermining footings necessitates careful examination of foundation designs and actual construction. In addition, it is vital that the structure be adequately anchored to the foundation. Uplift forces during a flood event are often great enough to separate an improperly anchored structure from its foundation should floodwaters reach such a height. CAVITY WALLS Wet floodproofing equalizes hydrostatic pressure throughout the structure by allowing floodwater to enter the structure and equalize internal and external hydrostatic pressure. Thus, any attempt to seal internal air spaces within the wall system is not only technically difficult, but also contrary to the wet floodproofing approach. Provision must be made for the cavity space to fill with water and drain at a rate approximately equal to the floodwater rate of rise and fall. Insulation within cavity walls subject to inundation should also be atypethat is not subject to damage frominundation. The design of foundation openings to equalize hydrostatic pressure is covered in the next section. Vi -W.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Protection of the Structure ' (continued) wet floodproofing may be issued for certain categories of structure. Refer to FEMA's Technical Bulletin #7-93, Wet Floodproofing Requirements for Structures Located in Special Flood Hazard Areas in Accordance with the NationalFlood Insurance Program. SOLID WALLS Solid walls are designed without internal spaces that could retain floodwater. Because these walls can be somewhat porous, they can absorb moisture and, to a limited degree, associated contaminants. Such intrusion could cause internal damage, especially in a cold (freeze-thaw) climate. Therefore, where solid walls are constructed of porous material, the retrofitting measures should include both exterior and interior protective cladding to guard against absorption. Pnninaarinn PrineinIcksand Practirce of I Retrnfittinn Flood-Prone Residential Structures VI -W.3 January1995 Chapter VI: General Design Practices Wet Floodproofing DESIGN OF OPENINGS IN FOUNDATION WALLS FOR INTENTIONAL FLOODING OF ENCLOSED AREAS BELOW THE FPE In buildings that are constructed on extended solid foundation walls or that have other enclosures below the FPE (that are not designed to resist flooding), it is important that the For additional informationonthe foundation contain openings that will permit the automatic regulations and design guidelines entry and exit of floodwaters. (See Figures VI-WI and VI- concerning foundation openings, W2.) please refer to FEMA Technical Bulletin #1-93, Openings in Foundation Wallsfor Buildings These openings allow floodwaters to reach equal levels on both Located in Special Flood Hazard sides ofthe walls and thereby lessen the potential for damage Areas in Accordance withthe fromhydrostaticpressure. While not arequirement for existing National Flood Insurance buildings built prior to a community'sjoining the NFIP, NFIP Program. regulations require these openings for all new construction and substantial improvements of existing buildings in SFHAs. The minimum criteria for design ofthese openings is as follows: FoundationOpening' I A minimum oftwo openings shall be provided on different with Vent I sides of each enclosed area, having a total net area of not \ _7$ less than one square inch for every square foot of enclosed BFE area subject to flooding. This is not required if openings are -] \ and certified. Eengineered 12' Maximum y-1 Bottom of Height L__10 4 9 pening a The bottom of all openings shall be no higher than one foot AboveGrade \ above grade. Li|Final Grade B!ockFoundation Openings must be equipped with screens, louvers, valves, L_ J or other coverings or devices that permit the automatic entry and exit of floodwaters. Figure VI-W 1: Typical Opening for Solid Foundation Wall VI -W.4 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design of Openings in Foundation Walls for Intentional Flooding of Enclosed Areas Below the FPE Maximum ; \ BFE_ _. e / oor J m [Attachedm Maximum ............ g FO G~arage BFE X Enclsed )i Lowetloor > -| v Fiished ;.?1 Area GradeX x > _ _ = X 1-Opening FoundationOpening Enclosed Area (Typical) Figure VI-W2: NFIP-Compliant Residential Building Built on Solid Foundation Walls with Attached Garage Fneiinaarinri Prinninlos and Prartircesrof Retrofittino Flood-Prone Residential Structures VI -W.5 January 1995 Chapter VI: General Design Practices '/Q Wet Floodproofing USE OF FLOOD-RESISTANT MATERIALS lose Detailedguidance is provided in FEMA Technical Bulletin 2-93, Flood-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. POPt Additional information on these elementscan be obtained from FEMA Technical Bulletin 7-93, Wet Floodproofing Requirements for Structures Located in Special Flood Hazard Areas in Accor- dance with the National Flood Insurance Program. In accordance with the NFIP, all materials exposed to floodwater must be durable, resistant to flood forces, and retardant to deterioration caused by repeated exposure to floodwater. Interior building elements such as wall finishes, floors, ceilings, roofs, and building envelope openings can also suffer consider abledamae from inundation by flood-waters, which can lead to failure or an unclean situation. The exterior cladding of a structure subject to flooding should be nonporous, resistant to chemical corrosion or debris deposits, and conducive toeasy cleaning. Interior cladding should be easy to clean and not susceptible to damage from inundation. Likewise, floors, ceilings, roofs, fasteners, gaskets, connectors, and building envelope openings should be constructed of flood-resistantmaterialsto minimize damagedunng and after floodwater inundation. Generally, these performance requirements indicate that masonry construction is the most suited to wet flood-proofing in terms of damage resistance. In some cases, wood or steel structures may be candidates, provided that the wood is pressure treated or naturally decay-resistant and steel is galvanized or protected with rust-retardant paint. Vi -W.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Building Operation and Maintenance Procedures and Emergency Preparedness Plans BUILDING OPERATION AND MAINTENANCE PROCEDURES AND EMERGENCY PREPAREDNESS PLANS The operational procedure aspect of applying floodproofing techniques involves both the structure's functional requirements for daily use and the allocation of space with consideration of each function's potential for flood damage. Daily operations and space use can be organized and modified to minimize damage caused by floodwater. FLOOD WARNING SYSTEM Because wet floodproofing will, in most cases, require some human intervention when a flood is imminent, it is extremely important that there be adequate time to execute such actions. This may be as simple as monitoring local weather reports, the National Weather Service alarm system, or a local flood warning system. INSPECTION AND MAINTENANCE PLAN Every wet floodproofing design requires some degree of periodic maintenance and inspection to ensure that all components will operate properly under flood conditions. Components of the system, including valves and opening covers, should be inspected and operated at least annually. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -W.7 January 1995 A A Chapter VI: General Design Practices Wet Floodproofing FLOOD EMERGENCY OPERATION PLAN This type of plan is essential when wet floodproofing requires human intervention, such as adjustments to or relocation of contents and utilities. A list of specific actions and the location of necessary materials to perform these actions should be developed. VI -W.8 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Protection of Service Equipment PROTECTION OF SERVICE EQUIPMENT The purpose ofthe retrofitting methods in this section is to prevent damage to structure, contents, and equipment caused '01* by contact with floodwaters by isolating these components from Serviceequipmentincludes floodwaters. Isolation ofthese components can take the form heating and air conditioning of relocation, elevation, or protection in place. systems, appliances, electrical/ plumbing systems, and water RELOCATION service/sewerfacilities. The most effective method of protection for equipment and contents is to relocate (permanently or temporarily) threatened items out of harm's way. The interior of the structure must be organized in a way that ensures easy access and facilitates relocation. ELEVATION Within the flood-prone structure, elevation of key items could be achieved through the use of existing or specially constructed platforms or pedestals. Contingent elevation can be accomplished by the use of hoists or an overhead suspension system. Relocated utilities placed on pedestals are subject to earthquake damage and must be secured to resist seismic forces. Figure VI-W3: ElevatedAir Conditioning Compressor EnaineerinaPrinciDlesand Practices of Retrofittina Flood-ProneResidential Structures VI-W.9 January 1995 Chapter VI: General Design Practices Wet Floodproofing IN-PLACE PROTECTION Some components can be protected in place through a variety of options, such as: * protective waterproof enclosures (flood-resistant bags); * anchors and tie-downs to prevent flotation; * low barriers or shields; and * protective coatings. FigureVI-W4: Flood Enclosure ProtectsBasement Utilities from Shallow Flooding Utility systems as used here are mechanical, electrical, and plumbing systems including water, sewer, electricity, telephone, cable TV, natural gas, etc. The recommendations presented in this section are intended for use individually or in common to mitigate the potential for flood-related damage. VI -W.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation FIELD INVESTIGATION Detailed information must be obtained about the existing structure to make decisions and calculations concerning the feasibility of using wet floodproofing. Use the Building/ Building System Data Sheets (Figures VI-3 and VI-4) as a guide to record information. Once this data is collected, the designer should answer the questions contained in Figure VI-W5, Wet Floodproofing Field Investigation Worksheet, to confirm the measure selected and develop apreliminary concept for the installation of wet floodproofing measures. Once a conceptual approach toward wet floodproofing has been developed, the designer should discussthe following items with the homeowner: * Previous floods and which equipment was flooded in prior floods and which previous appliances and branch circuits were affected by the floods. * Plan of action as to which equipment can be relocated and which equipment will have to remain located below FPE. * Length of power outages for work to be completed. * Specific scope of items to be designed. * Note any unsafe practices or code violations or exceptions to current codes. Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI-W.11 January 1995 Chapter VI: General Design Practices / Q Wet Floodproofing Owner Name: Prepared By: Address: Date: Property Location: Wet Floodproofing Field Investigation Worksheet El Flood protection elevation (FPE) required? El Can equipment be protected in place? -Yes -No O Is it feasible to install a curb or "pony" wall around equipment to act as a barrier? Yes No El Is it feasible to construct a waterproof vault around equipment below the FPE? _ Yes No o Can reasonably sized sump pumps keep water away from equipment? _ Yes No El Can equipment feasibly be relocated? O To a higherlocation on same floor level? -Yes -No o To the next floor level? -Yes No 171 Is room available for such equipment? -Yes -No E Can existing spaces be modified to accept equipment? _ Yes -No a Is additional space needed? Yes No a Do local codes restrict such relocations? Yes No a Electrical Questions al Is it feasible to relocate meter base and service lateral above FPE? -Yes No Cl Is it feasible to relocate main panel and branch circuits above FPE? -Yes -No El Is it feasible to relocate appliances, receptacles, and circuits above FPE? Yes No Cl Is it feasible to replace light switches and receptacles below FPE? -Yes No 1E Can ground fault circuit interrupter protection to branch circuits be added below the FPE? -Yes No VI Can service lateral outside penetrations be sealed to prevent floodwater entrance? Yes No E Can cables and/or conduit be mechanically fastened to prevent damage during flooding? _ Yes -No El Can splices and connections be made water resistant or relocated above FPE? _ Yes No 1 of 2 Figure VI-W5: Wet Floodproofing Field Investigation Worksheet VI -W.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation o MechanicalQuestions o If equipment is relocated, examine how related systems will be impacted including hot water/steam/condensate piping, cooling condensate drains, ductwork, and fuel supply. _ Yes_ No 0 If equipment is to be relocated, verify that adequate structural support and clearances for maintenance and repair exist at the new location. Yes -No O Can fire separation requirements be met? -Yes _ No SKETCH: 2 of 2 Figure VI-W5: Wet Floodproofing Field Investigation Worksheet (continued) Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI-W.13 January 1995 Chapter VI: General Design Practices ( Wet Floodproofing DESIGN OVERVIEW In this section we will present the process of design of wet floodproofing measures for utilities and appliances address ing applicable relocation, elevation, and protection in place considerations for each type of utility system and appliancenoted below: * ElectricalSystems * Central Heating Systems -Gravity Type Furnaces -Forced Warm Air Furnaces -Hot Water/SteamHeating Boilers -HeatPump Compressors * Central Cooling Systems * Ductwork Systems * Piping Systems * In-Space Heating Equipment * Water Systems * Sewer Systems * SepticTans 'Telephone Lines VI -W.14 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Overview * Cable TV Lines The general process of designing wet floodproofing measures involves developing apreliminary concept, verifying the concept with the homeowner, developing design details and specifications, verifying the design with the homeowner, preparing construction documents, and providing construction phase services. The key components of this process are presented below: MECHANICAL SYSTEMS * Make apreliminary sketch/floor plan showing location of mechanical systems. * Indicate proposed locations for shielding, relocation, or modifications. * Indicate modifications or relocations of related components. * Indicate materials of construction and means of access to equipment. * Determine how the shielding, relocation, or modifications may affect the structure and coordinate necessary modifications with a structural engineer. * Develop preliminary details of supports,hangers, piping/ ductwork, and equipment modifications. Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -W.15 January 1995 ChapterVI: General Design Practices Wet Floodproofing K %9 PIPING SYSTEMS * Make preliminary sketchof piping systems affectedby flooding. * Indicate proposed locations for relocation and/or additional anchorage. * Determine how relocation or modifications may affect the structure and coordinate necessary modifications with a structural engineer. * Develop preliminary details of supports, hangers, and pipingmodifications. TANKS * Make preliminary sketch of underground tanks and necessary provisions to prevent displacement or flotation. * Make preliminary sketch of above-ground tanks indicating anchoring/ballasting provisions to prevent displacement or flotation. VI -W.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Overview HOMEOWNER COORDINATION * Verify existing conditions related to all wet floodproofing measures being proposed. For Shielding Measures * Determine conditions at interface of shields and existing walls and floors. * Verify structural conditions and necessary provision for adequate support of wall. * Verify condition for means of access through or over wall for service and maintenance of equipment. For Relocation Measures * Verify existence of sufficient room for access and maintenance. * Verify structural conditions and necessary provisions for supporting equipment. * Verify re-routing of piping, fuel supply lines,venting, and ductwork. * Verify with the homeowner any restriction to proposed measures that may be imposed because of deed restrictions, zoning laws/subdivision restrictions, and local regulations. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.17 January 1995 Chapter VI: General Design Practices ,' Q Wet Floodproofing DEVELOPING DESIGN DETAILS AND SPECIFICATIONS * Prepare scale drawings of residence floor plans, as necessary, to show areas affected by the selected retrofitting measure. * Prepare details of installation of equipment at new locations, including proposed modifications to piping, fuel supply lines, venting, and ductwork. * Prepare details of new equipment supports or hanging provisions. * Prepare written specifications for the work, including general materials/products, and execution sections. VERIFY DESIGN WITH HOMEOWNER * Review with the homeowner the proposed retrofitting measures and details to ensure that they accurately reflect both the existing conditions and proposed improvements. PREPARE CONSTRUCTION DOCUMENTS * Prepare final construction drawings, including details for all measures proposed. * Make reference to applicable codes and regulations that govern the work. VI -W.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Overview * Indicate whether or not submission and review by authorities having jurisdiction is required. * Prepare final specifications. ELECTRICAL SYSTEMS Electrical system components can be seriously damaged by floodwaters when either energized or de-energized. Silt and grit accumulates in devices not rated for complete submergence and destroys the insulation value of the device. Current circuit breakers and fuses are designed to protect the wiring conductors and devices from overcurrent situations, including short circuit or ground fault conditions. Floodwaters seriously affect operation ofthese devices. Most homes were not designed to mitigate potential flood damage to electrical equipment; however, there are retrofitting steps that will provide permanent protection for the electrical system. * The chief concern is to raise or relocate equipment and devices above the FPE. * A second step is to seal outside wall penetrations, anchor cables and raceway, and mechanically protect the wiring system in flood-prone locations. * A third step is to seal out moisture. Electrical system problems occur as moisture permeates devices causing corrosion, which can lead to high resistance of electrical connections. * A fourth step necessary for retrofitting is the addition of ground fault circuit interceptors, which de-energize circuits when excessive current leakage is encountered. This step ultimately assists life safety protection and may be required by local code. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.19 January 1995 Chapter VI: General Design Practices Wet Floodproofing Each residence presents the designer with a unique set of characteristics including age, method of construction, size, and location. There are different combination systems that may need to be modified. When it is not feasible to elevate in place, the following information provides the design considerations and details that govern the retrofitting of electrical equipment and circuits below the FPE. * Receptaclesand switches shouldbe keptto aminimumand elevated as high as is practical. * Circuit conductors must be UL listed for use in wet locations. e Wiring should be run vertically for drainage after being inundated. * Outlet boxes should be corrosion-resistant and nonmetallic with weatherproof gaskets. * Lighting fixtures should be connected via simple screw base porcelain lampholders. This will allow for speedy removal of lamp or fixture, and the lampholder can be cleaned and reused. * Sump pumps and generators should have cables long enough to reach receptacles above the FPE. All circuits below the FPE should be ground fault interrupter protected. e -Wiring splices below FPE should be kept to a minimum. If conductors must be spliced, use crimp connectors and waterproof with heat shrink tubing or grease packs over the splice. VI -W.20 Engineerina PrinciDlesand Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Overview * Circuits serving equipment below the FPE should not also provide power to equipment above the FPE. This means power can be turned off to circuits below the FPE and not affect the rest of the home. * Electrical equipment and appliances relocated above the FPE should have new circuits installed. The electrical system should be designed in accordance with the National Electrical Code, local codes, and local utility company requirements. Prepare construction details and specifications as detailed below: * Show electrical floor plan and site plans for work to be completed by contractors. Include symbols, notes, and schedules. * Show new riser diagram if service is relocated or replaced. Show size of conductors and ground electrode conductor. * Note demolition of materials and work to be removed. * Size new circuit conductors and overcurrent protection to devices, equipment, and appliances. * Prepare specifications for work to be completed. EngineeringPrinciples and Practices of F Retrofitting Flood-Prone Residential Structures VI -W.21 January 1995 Chapter VI: General Design Practices L Q Y< Wet Floodproofing CENTRAL HEATING SYSTEM ALTERNATIVES The protection of central heating system equipment (i.e., furnaces, boilers, fan-coil airhandlers) requires consider ation of many factors. The designer must be sure that any protection or relocation of such equipment conforms to the requirementsset forth in local building codes and floodplain ordinances, state building codes, and equipment manufacturer's installation instructions. Some general points to consider are: * structural support for relocated equipment; £ maintenance of required equipment clearances and mainte- It nance access dictated by code and/or manufacturer; Most heating system equipment (i.e., furnaces, boilers, fan-coil air * provision of adequate combustion air for fuel-burning handling units) is designed and equipment; manufactured to operate in a particular orientation (i.e., vertical or horizontal).In most cases,the * maintenance ofproper venting offuel-burning equipment; equipment cannot be reconfigured and to operate in a different orientation. tion. * extension of fuel supply to relocated equipment. VI -W.22 Enqineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January1995 Design Overview In a post-flooding situation, the designer may recommend replacing an old furnace with a new one that meets current codes, is more energy/cost efficient, and fits in the desired location. Gravity Furnaces These furnaces depend on natural convective air circulation for operation and do not have a fan or blower. Therefore, they are installed at the lowest point in the heating system, usually in a basement below the living areas of the house. Because of this, alternatives for protection and/or relocation are limited. Potential alternatives may include: Raise Gravity Furnaces * Are non-combustible construction materials required under the furnace? * Extension or relocation offuel supply lines. Provide Protective Ring Wall or Vault * Does prevailing code allow waterproofvaults below FPE? * Can a curb or half-height waterproofpartition be provided for protection? * Are gravity furnaces allowed under present code? Enaineerina Princioles and Practices ofRetrofittina Flood-Prone Residential Structures VI -W.23 January 1995 Chapter VI: General Design Practices & P< > Wet Floodproofing Forced Warm Air Furnaces The fiunaces may exist in one of several configurationsupflow, downflow, or horizontal-and do not necessarily have the same constraints of location as gravity furnaces. In addition to the alternatives and considerations listed above, which are also applicable to forced wann air furnaces, there are the following: Relocate Furnace to a Higher Floor or Attic * Is space available? * Can floor support the weight of the furnace? * Is non-combustible flooring required underneaththe furnace? * Can furnace be reconnected to existing means for venting or is new venting more feasible? * Can the ductwork be reconfigured to connect to furnace at new location? * In case of relocation to an attic, is the furnace labeled for such a location? * Does a utility room above the FPE need to be constructed adjacent to the structure? VI -W.24 Enaineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Overview Some local codes recluire that piping located in floEA hazard zones be cap; ableof withstanding stress due to i hydrostatic and hydi rodynamic forces of floodwaters. HotWater Heating Boilers Most hot water heating boiler systems utilize a closed loop hot water piping loop to distribute heat. Considerations for relocation of heating boilers include: Can the boiler be placed on a high pedestal base to raise it above the FPE? The procedure may include: & Reconfiguration of breeching and modifications to chimney or vent pipe; 0 Modification of hot water or steam circulation piping; and! or * Modification offuel supply lines. Can the boiler be placed on an upper floor? Is there adequate space (codes generally dictate minimum clearances)? Can the boiler be reconnected to existing venting (i.e., chimney)? Is there space for an expansion tank? Does a utility room above the FPE need to be constructed adjacent to the structure? Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.25 January 1995 ChapterVI: General Design Practices o >K¾ WetFloodproofing Heat Pump Compressors The compressor in a heat pump system is generally located outdoors. To prevent damage, the compressor can be raised above the FPE or be relocated to a constructed above-FPE space inside or adjacent to the home, if possible. CENTRAL COOLING SYSTEM Central cooling systems include split system heat pump and air conditioners, ductless split systems, and packaged unitary equipment. Common components of all of these systems subject to damage from flooding include heat transfer coils, electric motors, controls, and compressors. Protection of these components from contact with floodwaters is strongly recommended for pre-FIRM structures and is required for substantially improved (damaged) or new structures. The designer should determine whether equipment can be protected by shielding or relocation. Shielding as used here means to provide a permanent barrier around equipment to prevent contact with floodwaters. The designer should investigate existing conditions and determine shielding and/or relocation measures that may be applied to protect cooling equipment. Indoor Units * Can shielding be provided to prevent floodwaters from contacting the indoor air handling unit? * Can unit be raised or located on the floor above? VI W.26 Enianeerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Overview Consider reconnection ofthe unit to existing or relocated ductwork; extension and/or relocation of refrigerant piping; and/or reconnection of the unit to the existing electrical power supply. Outdoor Units * Can outdoor unit feasibly be raised above the FPE? Ductwork * Refer to the discussion of ductwork under the next section. Unitary A/C Systems * Can unitary equipment be relocated above the BFE? DUCTWORK SYSTEMS Effects on flooded ductwork depend on the material of duct construction. Typically, galvanized steel or rigid ductboard is used for main ducts with flexible round duct runouts to individualoutlets. Generally, if wet by floodwaters, ducts made up of ductboard or similar materials are not reusable. Such duct materials, when wet, usually exhibit degradation of physical strength and insulating properties. In addition, these materials become soiled by water-borne contaminants and cannot be cleaned effectively. Galvanized steel ductwork is less susceptible to damage from flooding and may be cleaned after flooding. Ductwork can be damaged from the weight of infiltrated water when floodwaters recede. Access doors installed at low points in the duct system can provide a means of drainage for any ductwork subject to inundation. Normally these access doors would remain closed and would open only Engineering Principles and Practicesof Retrofitting Flood-Prone ResidentialStructures VI -W.27 January 1995 Chapter VI: General Design Practices Q Wet Floodproofing when flooding conditions were imminent. These access doors may also be used as a means of getting inside ductwork for cleaning after a flood. Internal acoustical linings or insulations in ductwork cannot be reused if they have come into contact with floodwaters. The typical linings and insulations are made of glass fiber and, as with ductboard, become contaminated from the floodwater and cannot be effectively cleaned afterward. Ducts with linings or internal insulations that are flooded should be replaced. External insulations should also be replaced if wet by floodwaters. Although some types of insulation, such as closed cell foam, may be water-resistant, all insulations used in the interior of ductwork are subject to contamination and should not be reused after contact with floodwater. To confirm alternatives for floodproofing of ductwork, determine the following: * Is there any ductwork below the FPE? * What is the existing construction material for ductwork below the FPE (galvanized steel, ductboard, or flexible duct runouts)? * If ductboard or flexible duct is checked, verify whether or not it can be replaced with insulated steel ductwork. * Can ductwork be located at high levels or in the attic? This may require reconfiguring air outlet layouts and the use of bulkheads to conceal ducts. * Does ductwork insulation need replacement? Internally insulated ducts probably will have to be replaced, as replacement of insulation in existing ductwork is usually not feasible. VI -W.28 Engineerina Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Overview * Steel ductwork with no interior insulation wet by floodwaters should be inspected, cleaned, and sanitized prior to reuse. PIPING SYSTEMS Potential damage to piping systems because of flooding includes: * Damage to thermal insulation of water piping; * Contamination of water piping by intrusion of floodwaters; * Breakage of piping due to hydrodynamic forces; * Clogging of building drain piping because of mud, silt, or debris; * Infiltration of floodwater into sewer and septic system; and * Surcharge (release) of sewage lines. Ofthese, only the first three canbe addressed by wet floodproofing measures. In selecting alternatives involving piping systems, determine the answers to the following: * Is piping below the FPE? * Can piping below the FPE be raised? It shouldbe determined whether it is more effective to leave piping at the existing location and provide adequate anchors to resist hydrodynamic forces or to relocate piping at a higher level. Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -W.29 January 1995 Chapter VI: General Design Practices K Y< ~ Wet Floodproofing If relocated, considerations against freezing may be required: * Can impervious pipe insulations be installed on pipes subject to becoming wet from floodwaters? * Can piping outlets be protected against intrusion of floodwaters? o Are pipes subject to hydrodynamic forces of floodwaters properly anchored? * Is piping provided with a proper sleeve and caulking at penetrations of exterior walls? * Surcharge of sewage lines must be considered. FuelSupply/Storage Applications In conjunction with floodproofing of heating equipment, the designer must consider rerouting andlor extending fuel supply lines (i.e., fuel oil, natural gas, and LPG) when equipment is relocated. Also, fuel storage tanks should be checked for proper support and anchorage to resist hydrostatic or hydrodynamic forces that act on such tanks during a flood. The following should be ascertained with respect to fuel supply/storage systems: * Can fuel lines be extended from existing point ofentry into the residence? * Does the fuel tank require relocation because of heating equipment relocation? * Is the existing fuel tank properly anchored to resist hydrostatic, hydrodynamic, and seismic forces? VI -W.30 Enaineerina PrinciDtes and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Overview IN-SPACE HEATING EQUIPMENT Residential "in-space" heating equipment refers to equipment located directly in the room (or space) to be heated. Such equipment may be permanently installed or portable. Gas room heaters and wall furnaces, oil/kerosene heaters, electric wall heaters, and electric baseboard heaters are examples of in- space heating equipment. If such equipment is below the FPE, the designer must determine whether such equipment feasibly can be raised above the FPE. The extent to which most equipment may be raised is limited by the fact that the equipment must remain in the room or space and that raising such equipment may reduce heating effectiveness. The designer should consult with the equipment manufacturer's installation recommendations before considering relocation. Room Heaters and Wall Furnaces * Can these items be raised? * Determine any modifications required to vents and fuel supplyprovisions. Oil/Kerosene Heaters * Can these items be raised? * Determine any modifications required to vents and fuel supplyprovisions. EngineeringPrinciples and Practices of IRetrofittingFlood-Prone ResidentialStructures VI -W.31 January 1995 Chapter VI: General Design Practices &P27e Wet Floodproofing Electric Heaters * Can wall units be reinstalled at a higher location in the wall? * Floor, kickspace, and baseboard units by nature of their design usually cannot be raised. If these heaters exist in the residence below the FPE, the designer should investigate the installation of alternative heaters such as electric wall heaters that may be installed above the FPE. WATER SYSTEMS On-site water systems continue to be a source of flood damages. Many modifications can be made inexpensively. The failure of these systems as a result of flooding can often lead to significant repairs that can tax an individual's already tight repair budget. Drinking Water Wells Private water systems can also be threatened by flooding. There is little one can do to protect a well that is in the floodplain. To avoid contaminating the water system beyond the well, residents should turn off the pump motor prior to the floodwater reaching the well. This should be preceded by the filling of bathtubs and other containers with potable water. The storage tank in the building will also provide a reservoir of potable water. The pump should not be turned on until the well has been inspected by a local health official or well repair professional followingthe flood. Should the pump not be turned off or if it is turned back on prematurely, the contaminated water in the well will be pumped into the building, thereby contaminating the plumbing in the building. Salt water contamination can damage VI -W.32 EngineerinoPrinciples and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Design Overview pumps and other mechanical systems like hot water heaters and furnaces in hot water-heated buildings. This will, of course, significantly increase that cost ofthe restoring the system after a flood. Shallow wells have a greater risk of being contaminated than do deep or artesian wells. Shallow wells are normally wider in diameter than artesian wells and therefore are more susceptible to surface water entering the well. The liners on shallow wells, usually concrete pipe without "O" ring gaskets, are generally not as well sealed as those in artesian wells, which are normally lined with cast or ductile iron pipe with tight-fitting pipejoints. Shallow wells, normally 10to 20 feet deep, are more susceptible to shallow groundwater contamination as well. Bacterial contamination poses the greatest threat to public safety. Salt water intrusion can leave the water brackish. Though this is distasteful, it is not a health risk in itself, but is more an indicator that the well has been contaminated and warrants further testing and analysis. Water service is critical to the continued safe and sanitary occupation of a building. Contamination of water systems can cause extensive delays in the reoccupancy of buildings after a flood. Water systems leading to and inside buildings can be a major sourceof flood damage. On-Site Portion of Water Systems Public water systems can become contaminated during a flood event. This contamination can spread to a building's water pipe system. Building occupants can do little to prevent the contamination of public water systems and should listen to instructions of local officials as to how to treat and use public water after a flood. To provide a source of potable waterto be used during and after a flood, residents should fill their bathtubs and various containers with clean water prior to the flood. Residents are normally told to do this by local officials as a precaution anyway. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.33 January 1995 ChapterVI: General Design Practices ONZ& Wet Floodproofing SEWER SYSTEMS On-site sewer systems continue to be a source of flood damages. Many modifications can be made inexpensively. The failure of these systems as a result of flooding can often leadto significant repairs that can tax an individual's already tight repair budget. On-Site Portion of Sewer Systems Sewage systems can generate a large portion of the contamination that occurs as a result of a flood. Since sewer lines are normally operated by gravity, they areusually found along rivers and creeks within the floodplain. In communities that have combined sanitary and storm sewers, sewage treatment plants are quite frequently overwhelmed, and untreated sewage is released into nearby rivers and creeks. There is little an individual can do to control this problem. Before a retrofit method(s) can be chosen, sewage threats must be identified as they affect the building under study. As an example, before one can predict whether or not a particular building is threatened by a sewer backup, one must find out if the building is served by a combined sewer system. These systems, when threatened with overwhelming stormwater, pose the greatest risk of backing up into a building. Even sewer systems that do not carry stormwater can back up due to floodwater infiltrating the system or sewage treatment plants being inundated by floodwater. The designer should contact the local sewer utility company to obtain information on the type of sewer system that serves the building and the history of sewer backups at that address and within the general area due to flooding. Only then can the designer decide what action(s) to take. VI -W.34 Enaineerina Princioles and Practices of Retrofittina Flood-Prone ResidIential Strucintumr January 1995 Design Overview Guidance concerning the anchoring of septic tanks is applicable to other types of underground storage tanks. In areas with combined sewers or a history of sewer backups, the installation of a sewer backflow prevention valve is recommended. This can range from a simple flapper type to more elaborate configurations that include a wastewater storage area for the building and/or a battery-operated wastewater injection system that forces the wastewater from the building out into the sewer system. These valves are illustrated in the Dry Floodproofing section of Chapter VI. This allows the sewer system in the building to continue to be used even when the public system is overwhelmed. Combination check and shear gate valves, also illustrated in the Dry Floodproofing section of Chapter VI, provide dual protection against backflow. The swing-check responds with instant closure when backflow starts. During emergency periods, when a serious backwater condition exists or is expected, or when the building drainage system is to be shut down, the manually operated shear gate is closed until the building drain line can be used again. The shear gate valve is kept open when the building drainage system is in use. The differential between the invert elevations ofthe inlet and outlet provides a cleaning action ofthe effluent, which reduces fouling ofthe check seat. Simple backflow valves are usually available through local plumbing contractors. More elaborate systems are normally available through specialty contractors. SEPTIC TANKS On-site systems consisting of septic tanks and leach fields are often seriously affected by flooding. The buoyancy effects on tanks and the negative effects caused by the release of sewage pose significant health risks. The leach field can be damaged by the intrusion of floodwater. Leach field piping partially filled with fresh water (sewage water) can become buoyant when submerged and result in the possibility that the pipe may lift out ofthe ground. This action can obviously result in significant damage and resulting repair costs. Ennineerina Princinles and Practices of F letrofittina Flood-Prone Residential Structures VI -W.35 January 1995 Chapter VI: General Design Practices Wet Floodproofing I When flooding inundates a septic tank, proper anchorage is needed to prevent the movement and flotation ofthe tank. If it moves, it can rupture connecting piping, burst up out of the irces,When subject to flood ft ground, and present a hazardous condition. The worst design naturalstorage tanks containing conditions for anchorage of underground tanks occur when the rdditonal ronmengas or oil also pose the a risk of explosion or envi tal contamination. tank is empty and is covered by floodwaters or high ground water. Unless proper anchorage is utilized, the buoyancy forces acting on the tank will cause the tank to float out of the ground. The anchorage of any tank system consists of attaching the tank to a resisting body with enough weight to hold the tank in place. The attachment, or anchors, must be able to resist the total buoyant force acting on the tank. The buoyant force on an empty tank is the volume ofthe tank multiplied by the specific weight ofwater. it is usually advisable to include a factor of safety of 1.3, as is shown in the following buoyancy force computation: _ w e Fb= 0.134 Vt yFS -Wt where: Fb is the buoyancy force ofthe tank, in pounds; Vt is the volume ofthe tank in gallons; 0.134 is a factor to convert gallons to cubic feet; y is the specific weight of fresh water (62.4 lbHP); FS is a factor of safety to be applied to the computation, typically 1.3 for tanks; and Wt is the weight ofthe tank. Formula VI-WI: Buoyancy Force on a Tank VI -W.36 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Overview The volume of concrete required to offset the buoyant force of the tank can be computed as follows: V = Fb/(Sc where: VC is the volume of concrete required, in cubic feet; Fb is the buoyancy force ofthe tank in pounds; S c is the effective weight of concrete, typically 150 pounds per cubic foot; and or is the specific weight of water (62.4 lb/ft 3 ). Formula VI-W2: Concrete Volume Required to Offset Buoyancy To resist this buoyant force, a slab of concrete with a volume, VC, is usually strapped to the tank to resist the buoyant load. TELEPHONE SYSTEMS Telephone systems can be damaged by floodwaters. Exterior demarc terminal boxes and transient protectors typically owned by the telephone company may require replacement and/or relocation above the flood protection elevation. These devices receive silt and grit damage, and corrosion may occur on terminals and connectors when inundated. Four-wire residential telephone cable-type CM is not rated as waterproof or for exterior usage. The cables and outlet (type RJ- I1) modularjacks should be relocated above the FPE. Building penetrations for telephone cable should be sealed to keep out moisture and water. All telephone company cables from underground or overhead locations should be waterproofed with either heavy-duty insulated cable as in aerial drop cable or petroleumjelly-filled cable rated for direct burial and submersible operation. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.37 January 1995 Chapter VI: General Design Practices Wet Floodproofing CABLE TV SYSTEMS Indoor cable (CATV) wiring systems can be damaged by floodwaters due to mechanical damage and by corrosion and deterioration of the center coax conductor and shield wires. CATV terminations (F Connectors) do not readily admit moisture due to their design. Exterior-rated coaxial cable is petroleumjelly-filled and poses no problems by being inundated with floodwaters. Relocate CATV cables, outletjacks, and wall plates to above the FPE. VI -W.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Construction CONSTRUCTION ELECTRICAL The electrical relocation should follow current NEC (Na tional Electrical Code NFPA 70) requirements and generally involves relocating like equipment or replacing it with similar equipment. Local codes and the building officials having jurisdiction should be contacted for coordination during design to ascertain any special requirements. The local utility should be contacted when relocation ofthe service lateral, metering equipment, or service location is to be moved or relocated. If power is to be disconnected from the house, the local utility company should be contacted and advised of this condition. Specific electrical system checks should include: * Check for correct cable size and breaker sizes per drawings in the field. * Require inspection before concealing work. * Verify that local jurisdiction will provide inspection when done. * Check grounding; test receptacles with tester. * Check light and appliance operation. * Review workmanship and wiring methods. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -W.39 January1995 ChapterVI: General Design Practices X > Wet Floodproofing MECHANICAL In conformance with the conditions of the construction contract, the designer shall perform inspection of the work during construction. Typical mechanical system checks should include: Check relocated or modified equipment for proper installation, orientation, and operation. e o Require inspection before concealing work. * Check wall penetrations for sealing and insulation. * Check piping, vent, ductwork, and fuel line connections. * Check supports for equipment and piping, vent, ducts and fuellines. VI -W.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Floodwalls Table of Contents Types of Floodwalls ............................... VI -F.2 Gravity Floodwall ............................... VI -F.3 CantileverFloodwall ............................... VI -F.5 Counterfort Floodwall ............................... VI -F.9 ButtressedFloodwall ............................... VI -F.10 FieldInvestigation ............................... VI-F.11 Design ............................... VI -F.14 Floodwall Design (Selection and Sizing) ....... ........................ VI -F.14 Sliding ............................... VI -F.16 Overturning ............................... VI -F.16 Pressure ............................... VI -F.16 Floodwall Sample Calculation ............................... VI -F.36 Floodwall Design -Simplified Approach ............................... VI -F.42 Floodwall Appurtenances ............................... VI -F.46 Floodwall Closures ............................... VI -F.46 Drainage Systems ............................... VI -F.55 Seepage and Leakage ............................... VI -F.60 Seepage Throughthe Floodwall ............................... VI -F.60 Seepage Under the Floodwall ............................... VI -F.61 Leakage Between the Floodwall and Residence ............................ ........... VI -F.62 Architectural Details ....................................... VI -F.63 Maintenance Considerations ....................................... VI -F.70 Construction ....................................... VI -F.73 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi-F.i January 1995 FLOODWALLS A properly designed and constructed floodwall can often be an effective device for repelling floodwaters. Floodwalls are typically used in three roles: * as a barrier against inundation, * as a defense for unequalized hydrostatic and hydrodynamic loading situa- tions, and * to deflect debris and ice away from the structure. The selection of a floodwall design is primarily dependent on the type of flooding expected at the building's site. High water levels and velocities can exert hydrodynamic and hydrostatic forces and impact loads, which must be accounted for in the floodwall design. The composition of any type of floodwall must address three broad concerns: * Overall stability of the wall as related to the external loads, * Sufficient strength as related to the calculated internal stresses, and * Ability to provide effective enclosures to repel floodwaters. These internal and external forces pose a significant safety hazard if floodwalls are not properly designed and constructed, or their design level of protection is overtopped. Additionally, a tall floodwall can become very expensive to construct and maintain and can require additional land area for grading and drainage. Therefore, in most instances, residential floodwalls are practical only up to a height of three to four feet above existing grade, although residential floodwalls can be and are engineered for greater heights. Under NFIP regulations, floodwalls are not recognized as acceptable retrofitting measures for new and substantially improved (or damaged) struc- tures. Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures VI-F.1 January 1995 Chapter VI: General Design Practices O19 >~ Floodwalls TYPES OF FLOODWALLS Figures VI-F 1 and VI-F2 illustrate the use of floodwalls in 46 residential applications. Figures VI-F3 and VI-F4 illustrate Placement of floodwalls in the several types of floodwalls including gravity, cantilever, floodwayis not allowed under buttress, and counterfort. The gravity and cantilever flood- local floodplain regulations. walls are the more commonly used types. Figure VI-F 1 Typical Residential Floodwall Figure VI-F2: Typical Residential Floodwall VI -F.2 Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Types of Floodwalls Floodwall Types FPE _W FPEF heel toe Gravity Wall Cantilever Wall Figure VI-F3: Gravity and Cantilever Floodwalls Alternative Floodwall Types Buttress Counterfort Figure VI-F4: Buttress and Counterfort Floodwalls GRAVITY FLOODWALL A gravity floodwall depends upon its weight-as its name implies-for stability. Thegravity wall's structural stability is attained by effective positioning of the mass of the wall, rather than the weight of the retained materials. The gravity wall resists overturning primarily by the dead weight of the concrete and masonry construction. It is simply too heavy to be overturned by the lateral flood load. EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VI -F.3 January 1995 ChapterVI: GeneralDesign Practices Floodwalls Frictional forces between the concrete base and the soil foundation generallyresist sliding of the gravity wall. Soil foundation stability is achieved by ensuring that the struc ture neither moves nor fails along possible failure surfaces. Figure VI-F5 illustratesthe stability of gravity floodwalls. Gravity walls are appropriate for low walls or lightly loaded walls. They are relatively easy to design and construct. The primary disadvantage of a gravity floodwall is that a large volume of material is required. As the required height of a gravity floodwall increases, it becomes more cost effective to use a cantilever wall. Stability of Gravity Floodwalls A = Height of Floodwall C = Width of Top L = Width of Bottom P = Dead Weight \ _ Toe Dt If-Point of Rotation *_`=_ -Base Friction Figure VI-F5: Stability of Gravity Floodwalls VI-F.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Floodwalls -'Wh Reinforced concrete provides an excellent barrier in resisting water seepage, since it is monolithic in nature. The reinforcement not only gives the wall its strength, but limits cracking as well. CANTILEVER FLOODWALL A cantilever wall is a reinforced-concretewall (cast-in-place or built with concrete block) that utilizes cantilever action to retain the mass behind the wall. Reinforcement of the wall is attained by steel bars embedded within the concrete or block core of the wall (illustrated by Figure VI-F6). Stability of this type of wall is partially achieved from the weight of the soil on the heel portion of the base, as illustrated in Figure VI-F7. Figure VI-F6: Concrete Cantilever Floodwall Reinforcement EngineeringPrinciples and Practices of Retrofitting Flood-Prone Residential Structures VI-F.5 January 1995 Chapter VI: General Design Practices Floodwalls Stability of Cantilever Floodwalls Figure VI-F7: Stability of Cantilever Floodwalls The floodwall is designed as a cantilever retaining wall, which takes into account buoyancy effects and reduced soil bearing capacity. However, other elements of a floodproofing project (i.e., bracing effects of any slab-on grade, the crosswalks, and possible concrete stairs) may help in its stability. This results in a slightly conservative design for the floodwall but provides a comfortable safety factor when considering the unpredictability of the flood. Backfill can be placed along the outside face of the wall to keepwater away from the wall during flooding conditions. VI -F.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Typesof Floodwalls Figure VI-F8: Typical Reinforced Concrete Floodwall 6 While the double-faced brick floodwall application is used on either side of concrete block with cores reinforced and grouted, experience has indicated it is not as strong or leakproof as mono lithic cast-in-place applications. Information and details for a standard reinforced concrete floodwall are provided in case studies 4, 5, and 6 in Chapter VII. The concrete floodwall may be aesthetically altered with a double-facedbrick application on either side of the monolithic cast-in-place reinforced concrete center (illustrated in Figure VI-F8). This reinforced concrete core is the principal structural element of the wall that resists the lateral hydrostatic pressures and transfers the overturning moment to the footing. The brick-faced wall (illustrated in Figures VI-F9 and VI-F10)is typically used on homes with brick facades. Thus the floodwall becomes an attractive modification to the home. In terms of the structure, the brick is considered in the overall weight and stability of the wall and in the computation of the soil pressure at the base of the footing, but is not considered to add flexural strength to the floodwall. Engineering Principles and Practices of IRetrofittingFlood-Prone Residential Structures VI-F.7 January 1995 Chapter VI: General Design Practices Floodwalls Brick Venee r Over Cast-in-Place Concrete Floodwall Typical Section (Cantilever Design) not to scale NOTE: Face Brick to Match Ex Brick| 3/4- Chamfer Typ. 7_ e 4' Brick- Conc. Patio 1/2- Cork_ 4-CMU 3- CLR Figure VI-F9: Typical Section of a I Brick-FacedConcrete Floodwall VI -F.8 Engineering Principle. s and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Types of Floodwalls Figure VI-F IO: Typical Brick-Faced Concrete Floodwall When the flood protection elevation requirements of a gravity or cantilever wall become excessive in terms of material and cost, alternative types of floodwalls can be examined. The use of these floodwall alternatives is gener ally determined by the relative costs of construction and materials and amount of reinforcement required. COUNTERFORT FLOODWALL A counterfort wall is similar to a cantilever retaining wall, except that it can be used where the cantilever is long or when very high pressures are exerted behind the wall. Counterforts, or intermediate traverse support bracing, are designed and built at intervals along the wall and reduce the design forces. Generally, counterfort walls are economical for wall heights in excess of 20 feet, but are rarely used in residential applications. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.9 January 1995 Chapter VI: General Design Practices Floodwalls BUTTRESSED FLOODWALL A buttressed wall is very similar to a counterfort wall. The only difference between the two is that the transverse support walls are located on the side of the stem, opposite the retained materials. The counterfort wall is more widely used than the buttress because the support stem is hidden beneath the retained material (soil or water), whereas the buttress occupies what may otherwise be usable space in front of the wall. VI -F.10 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation FIELD INVESTIGATION Detailed information must be obtained about the site and existing structure to make decisions and calculations concerning the design of a floodwall. The designer should utilize the guidance presented in this chapter where detailed information and checklists for field investigation are presented. Key information to collect includes the low point of elevation survey, topographic and utilities surveys, hazard determinations, local building requirements, and homeowner preferences. Once the designer has developed the above- mentioned low point of entry and site and utility survey information, a conceptual design of the proposed floodwall can be discussed with the homeowner. This discussion should cover the following items: * Previous floods and which areas were flooded or affected by floods. * A plan of action as to which opening(s) and walls of the structure can be protected by a floodwall and floodwall closures. * Evidence of seepage/cracking in foundation walls, which would indicate the need to relieve hydrostatic pressure on the foundation. * A plan of action to use a floodwall to relieve hydrostatic pressure on the foundation and other exterior walls. * The various floodwall options and conceptual designs that would provide the necessary flood protection. Obtain consensus on the favored type, size, location, and features of the floodwall(s). * A plan of action as to which utilities need to be adjusted or floodproofed as a result of the floodwall. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures vi -F.1 1 January 1995 Chapter VI: General Design Practices Floodwalls A plan of action for construction activity and access! egress to convey to the owner the level of disruption to be expected. The designer of a floodwall should be aware that the con struction of these measures may not reduce the hydrostatic pressures against the below-grade foundation of the struc ture in question. Seepage beneath the floodwall and the natural capillarity of the soil layer may result in a water level inside the floodwall that is equal to or above grade. This condition is worsened by increased depth of flooding out side the floodwall and the increased flooding duration. Unless this condition is relieved, the effectiveness of the floodwall maybe compromised. This condition is illus trated in Figure VI-F 11. -I \_ Zone of Phreatic Surface Saturated Soil Figure VI-FI 1: Seepage Underneath a Floodwall It is important that the designer check the ability of the existing foundation to withstand the saturated soil pressures that would develop under this condition. The computations necessary for this determination are provided in Chapter IV. VI -F.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation The condition can be relieved by installation of foundation drainage (drainage tile and sump pump) at the footing level, and/or by extending the distance from the foundation to the floodwal. The landside seepage pressures can also be decreased by placing backfill against the flood side of the floodwall to extend the point where floodwaters submerge the soil, but the effectiveness of this measure depends on the relative Determination of an appropriate characteristics of the soils in the foundation and the backfill. distance from the structure for the The design of foundation drains and sump pumps is presented floodwall is a function of the in the Chapter VI Dry Floodproofing section. depth of the foundation. The deeper the lowest level of the structure, the furither away the Computation of the spacing required to obviate the problem is floodwall should be placed. a complicated process that should be done by an experienced geotechnical engineer. Figure VI-F12 illustrates the change in phreatic surface as a result of increasing the distance between the foundation and the floodwall and/or the installation of a foundation drain and sump pump system. ir External Floodwall Floodwall r nFlood Protection Elevation Patio Foundation Drain to S :p 'SK,16No Phreatic Surface Saturated Soil Figure VI-F12: Reducing Phreatic Surface Influence by Increasing Distance from Foundation to Floodwall Enaineerina Principles and Practices of RetrofittingFlood-Prone Residential Structures VI -F.13 January 1995 Chapter VI: General Design Practices Floodwalls DESIGN FLOODWALL DESIGN (SELECTION AND SIZING) The permeability of concrete The design of floodwalls consists of the proper selection block may necessitate the use of a monolithic core or the application sizig of the actual floodwall and the specification of of sealants to eliminate seepage appurtenances such as drainage systems; waterproof materithroughthe wall. als to stop seepage and leakage; and miscellaneous details to meet site and homeowner preferences for patios, steps, wall facings, and support of other overhead structures (posts and columns). The structural design of a floodwall to resist anticipated flood and flood-related forces presented in Chapter IV follows the seven-step process outlined in Figure VI-F 13. VI -F.14 Enaineerina PrinciDlesand Practices of RetrofittinaFlood-Prone Residential Structures January 1995 Design Floodwall Design Process Calculate Factor of Safety against Overturning, FS(OT) Figure VI-F13: Floodwall Design Process Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.15 January 1995 ChapterVI: General Design Practices Floodwalls Failure by Sliding FPE , Sliding Force : Heel, _ Toe Figure VI-F14: Failure by Sliding Figure VI-F15: Failure by Overturning Figure VI-F16: Failure Due to Excessive Pressure In general the stability of the floodwall should be investigated for different modes of failure. Sliding A wall including its footing may fail by sliding if the sum of the lateral forces acting upon it is greater than the total forces resisting the displacement. The resisting forces should always be greater than the sliding forces by a factor of safety. (See Figure VI-F14.) Overturning Another mode of failure is overturning about the foundation toe. This type of failure may occur if the sum of the overturning moments is greater than the sum of the resisting moments about the toe. The sum of resisting moments should be greater than the sum of the overturning moments by a factor of safety. (See Figure VI-Fl 5.) Pressure Finally, a wall may fail if the pressure under its footing exceeds the allowable soil bearing capacity. (See Figure VIF16.) In the following paragraphs, the step-by-step process for completing the structural design of a floodwall is presented, followed by an example illustrating the use of the formulas. Table VI-F I provides soil information that is necessary in the computations that follow. VI- F.16 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design TableVI-FI Soil Factors for Floodwall Design Soil Type Allowable Bearing Coefficient of Friction, Cf Pressure, S,, In pounds per square foot Clean, dense sand and gravel, GW, GP, SW and 2,000 0.55 SP Dirty sand and gravel of restricted permeability, 2,000 0.45 GM, GM-GP, SM, and SM-SP Firm to stiff slits, clays, silty fine sands, clayey 1,500 0.35 sands and gravel, CL, ML, CH, SM, SC, and GC Soft clay, silty clay, and 600 0.30 silt, CL, ML, and CH Step 1: Determine wall height and footing depth. 1. Determine wall height based on flood protection elevation, which equals the design flood elevation plus one foot. The extra one foot is the minimum recommended freeboard as a safety measure against future flood levels that exceed the design flood. 2. Determine minimum footingdepth based on the frost depth, local code requirements, and the soil condition. The footing should rest on suitable natural soil or on controlled and engineeredbackfill material. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.17 January 1995 Chapter VI: General Design Practices Floodwalls Step 2: Determinedimensions. Based on the following guidelines or reference to engineering handbooks, assume dimensions for the wall thickness, footing width, and footing thickness. 1. The choice of wall thickness depends on the wall material, the strength of the material, and the height of the wall. Typical wall thicknesses are 8, 12, and 16 inches for masonry, concrete, or masonry/concrete walls. 2. The footing width depends on the magnitude of the lateral forces, allowable soil bearing capacity, dead load, and the wall height. The typical footing width is the proposed wall height. Typically the footing is located under the wall in such a manner that 1/3 of its width forms the toe and 2/3 of the width forms the heel of the wall as shown in Figure VI-F 17. Typical footing thicknesses are based upon strength requirements and include 8, 12, and 16 inches. Step 3: Determine forces. There are two types of forces acting on the wall and its footing: lateral and vertical. These forces were discussed in Chapter IV and are illustrated in Figure VI-F 17. VI -F.18 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Forces Acting on a Typical Floodwall 6 A -Hydrostatic Buoyancy Pressure F62 2Bearingqmex) ~'-L4..JJIIIIII Soil _M~n)___ _ Pressure Figure VI-F17: Forces Acting on a Floodwall 1. Lateral forces: These forces are mainly the hydrostatic and differential soil/water forces behind the wall, and the saturated soil force in front of the wall. Hydrostatic and soil forces are as described in Chapter IV -Determination of Hazards. =nnindmrinn Prinninlha andl Practircme of Retrnfittine Flood-Prone Residential Structures VI -F.19 Januarv 1 995 Chapter VI: General Design Practices Floodwalls 2. Vertical forces: The vertical forces are buoyancy and the various weights of the wall, footing, soil, and water acting upward and downward on the floodwall. The buoyancy force, FbW acting at the bottom of the footing is computed as follows: ;ODD I' Fb= Fbi* b2 = lbs with F bi and Fb2 computed as follows: Fbl=1/2yHB (From Formula IV-8) F 2 =1/2yD B (From Formula IV-8) where: Fb is the total force due to buoyancy, in pounds; Fbl is the buoyancy force, in pounds, due to hydrostatic pressure at the floodwall heel acting at a distance of B/3 from the heel; Fb2 is the buoyancy force, in pounds, due to hydrostatic pressure at the floodwall toe, acting at a distance of B/3 from the toe; Y is the specific weight of water (62.4 pounds per cubic foot); B is the width of the footing, in feet; H is the floodproofing design depth, in feet; Dt is the depth of soil above the floodwall toe, in feet. (See Figure VI-F17) Formula VI-FI: Buoyancy on a Floodwall VI-F.20 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design The gravity forces acting downward are: * the unit weight of floodwall (Ww.1); I wall ll lbs/LF where: Wwali is the weight of the wall, in pounds; H is the floodproofing design depth in feet; tftg is the footing thickness, in feet; twall is the wall thickness, in feet; Sg is the unit weight of wall material (concrete is 150 pounds per cubic foot); (See Figure VT-F17) Formula VI-F2: Floodwall Weight * the unit weight of the footing (Wftg); = B tftgSg = lbsALF ik W~~'ftg where: Wftg is the weight of the footing, in pounds; B is the width of the footing, in feet; tftg is the footing thickness, in feet; Sg is the unit weight of wall material (concrete is 150 pounds per cubic foot) (See Figure VI-F17) Formula VI-F3: Footing Weight Engineerinrgi ri. rh --' and Practices of Retrofitting Flood-Prone Residential Structures VI -F.21 January 1995 Chapter VI: General Design Practices Floodwalls * the unit weight of the soil over the toe (WYQ; flu I1oI loII LMs': Wst= C(D' -tftg)(701i) = lbs/LF where: WN, is the weight of the soil over the toe, in pounds; C is the width of the footing toe, in feet; Dt is the depth of the soil above the floodwall toe, in feet; tftg is the footing thickness, in feet; y7oj is the unit weight of the soil, in pounds per cubic foot. (See Figure VI-F17) The unit weight of the soil, yl.o Formula VI-F4: Weight of Soil Over Floodwall Toe can be obtained from the soil survey, engineering texts, or a * the unit weight of the soil over the heel (W1h); and geotechnical engineer. Wah = Ah(Dh-tfg)(ysoi-62.4) = lbs/LF where: Wb, is the weight of the soil over the heel, in pounds; Ah is the width of the footing heel, in feet; Dh is the depth of the soil above the heel, in feet; tags is the footing thickness, in feet; , is the unit weight of the soil, in pounds per cubic foot. (See Figure VI-F17) Formula VI-F5: Weight of Soil Over Floodwall Heel VI- F.22 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design * the unit weight of the water above the heel (Wwh). i Q I .I Wvh = (Ah)(H -tftg)(62.4)= _bs/LF where: Wwh is the weight of the water above the heel, in pounds; Ah is the width of the footing heel, in feet; H is the floodproofing design depth, in feet; tftg is the footing thickness, in feet; (See Figure VI-F17) Formula VI-F6: Weight of Water Above Floodwall Heel The total gravity forces acting downward, WG,in pounds can be computed as the sum of the individual gravity forces: Formula VI-F7: Total Gravity Forces Per Linear Foot of Wall Therefore the net vertical force, Fv,is then calculated as: Formula VI-F8: Net Vertical Force Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.23 January 1995 Chapter VI: General Design Practices FloodwalIs Step 4: Check sliding. This step involves the computation of the sliding forces, the forces resisting sliding, and the factor of safety against sliding. For a stable condition, the sum of forces resisting sliding should be larger than the sum of the sliding forces. 1. Sliding Forces: The sum of the sliding (lateral hydrostatic, hydrodynamic, and impact) forces, FH' is computed as follows: FH= Fh+ Fdif+ (Fdh or Fd)+ (F. or F) = lbs where: FH is the cumulative lateral hydrostatic force acting at a distance H/3 from the point under consideration, in pounds; Fh is the lateral hydrostatic force due to standing water in pounds; and F jf is the differential soil/water force acting due to combined freestanding water and saturated soil conditions, in pounds. Fdh is the equivalent hydrostatic pressure due to low velocity. flood flows, in pounds; Fd is the hydrodynamic force against the structure due to high velocity flood flows, in pounds; Fn is the normal impact force in pounds, and Fs is the special impact force in pounds. The computation of FH 9 Fdp Fdh9 F FATand F. is presented in Formulas IV-4, IV-6, IV-10, IV-13, IV-14, and IV-15. (See Figure IV-17) Formula VI-F9: Sliding Forces VI -F.24 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design 2. Resisting Forces: The forces resistant to sliding are the frictional force, Ffrqbetween the bottom of the footing; the cohesion force, FC,between the footing and the soil; and the soil and the saturated soil force, Fp, over the toe of the footing. These resisting forces are computed as follows: a. Frictional Foc: The frictional force, Ffrpbetween the bottom of the footing and the soil is a function of net vertical force, FVqtimes coefficient of friction, Cr The coefficient of friction, C. between the base and the soil depends on the soil properties. (See Table VI-F 1). Ffr = Cf FV= lbs where: Ffr is the friction force between the footing and the soil, in pounds; C, isthe coefficient of friction between the footing and the soil; and FY is the net vertical force acting on the footing, in pounds, as was previously presented in Formula VI-F8. Formula VI-FIO: Frictional Forces Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.25 January 1 995 Chapter VI: General Design Practices Floodwalls b. Cohesion Force: The cohesion force between the base and the soil, F,, is obtained by multiplying the width of the footing, B, by the allowable cohesion value of the soil. This allowable cohesion value is usually obtained from a geotechnical analysis of the soil. The cohesion between the footing and the soil may be destroyed or considerably reduced due to contact from water. Due to potentially high variations in the allowable cohesion value of a soil, the cohesion is usually neglected in the calculations; unless the value of cohesion is ascertained by soil tests or other means, it should be taken as zero in the calculations. F = CB= lbs - ~~~~~C S where: F is the cohesion force between the base and the soil in pounds; C is the allowable cohesion in pounds per square foot (usually assumed to be zero), and B is the width of the footing, in feet. (See Figure VI-F17) Formula VT-Fl 1: Cohesion Force VI -F.26 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 . Design c. Saturated Soil Force Over the Toe: The saturated soil force over the toe, FP,is calculated as: Fp =2 [kP (Yso_ y)+y]Dt= lbs where: FP is the passive saturated soil force over the toe, in pounds; 7'.iI is unit weight of the soil (pounds per cubic foot); and Dt is the depth of the soil over the floodwall toe, in feet. kp is the passive soil pressure coefficient Y is the specific weight of water in The passive soil pressure coeffi- cient, k , typically ranges from 2-lbs/ft3 . 5. Typical values are 2 for plastic clays, 3 for clayey silts and poorly (See Figure VI-F17) graded gravels, and 3-4 or well graded sands. Consult a Formula VI-F12: Saturated Soil Force Over Floodwall Toe geotechnical engineer for more precise values. The sum of the resisting forces to sliding, FR, is calculated as the sum of the individual resisting forces to sliding, as shown below. FRFII X ~FR =Ff + FC+ F= Ilbs Formula VI-F 13: Sum of Resisting Forces to Sliding Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.27 January 1995 / 1.5 where: FS(SL) is the factor of safety against sliding (should be greater than 1.5); FR is the sum of the forces resisting sliding in pounds; and FH is the sum of the sliding forces (cumulative lateral hydrostatic force) in pounds. Formula VI-F14: Factor of Safety Against Sliding The factor of safety against sliding should be at least 1.5. If the factor of safety is determined to be less than 1.5, the designer should lower the footing, increase the amount of fill over the footing, and/or change the footing dimensions, then go back to Step 3 and try again (as is illustrated in the flow chart for design of floodwall). Step 5: Check overturning. The potential for overturning should be checked about the bottom of the toe (Figure VI-F5). For a stable condition, the sum of resisting moments, MR,should be larger than the sum of the overturning moments, MO' The ratio of MRover MO is called the Factor of Safety against overturning, FS(OT). 1. Overturning Moments: The overturning moments are due to hydrostatic and hydrodynamic forces, impact loads, saturated soil, and the buoyancy forces acting on VI -F.25 cgqineerinq Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 '-I,'~~~~~~: When hydrodynamic input loads act on the floodwall sections parallel to the flow and the downstream facing wall, Formulas VI-F9 and VI-F15 will produce conservative results. Further detailed analysis may result in smaller sections and a corresponding reduction in cost. Design the footing. The sum of the overturning moments, Mo, is calculated as: -M' MO =Fh(H/3)+Fdif(D/3)+Fbl(2B/3)+ r,-.0g I [Fdh(H/2) or Fd(H-Dh/2 + Dh)] +(FnH or FSH)+Fb2(B/3)= foot-lbs Vihere: MO is the sum of the overturning moments, in foot-lbs; Fh is the lateral hydrostatic force due to standing water, in pounds (Formula IV-4); Fdif is the differential soil/water force acting due to combined freestanding water and saturated soil conditions (Formula IV-6); Fbi is the buoyancy force, in pounds, due to hydrostatic pressure at the floodwall heel acting at a distance of B/3 from the heel, (Formula VI-Fl); Fb2 is the buoyancy force, in pounds, due to hydrostatic pressure at the floodwall toe, acting at a distance of B/3 from the toe, (Formula VI-Fl); Fdh is low velocity force (Formula IV-10); Fd is hydrodynamic force (Formula IV-13); Fn is normal impact force (Formula IV-14); Fs is special impact force (Formula IV-1 5); B is the width of the footing, in feet; H is the height of the wall, in feet; D is the height of the soil above the heel, in feet; and * h is the depth of the soil above the heel, in feet. Formula VI-F15: Sum of Overturning Moments Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.29 January 1995 Chapter VI: General Design Practices Floodwalls 2. Resisting Moments: The resisting moments are due to all vertical downward forces and the lateral force due to soil over the toe. The sum of resisting moments, MR,is calculated as: 10001 [.ilMR = W W.,,(C+(tw 1I2)) + Wftg (B/2) + Ws (C/2) + WSh (B-(Ah/2)) + WWh (B( Ah/2)) + Fp (Di/3)= foot-lbs where: MR is the sum of the resisting moments in foot-lbs; Wwa81 is the weight of the wall, in pounds; t is the wall thickness, in feet; Wftg is the weight of the footing, in pounds, (Formiula VI-F3); B is the width of the footing, in feet; Wst is the weight of the soil over the toe, in pounds, (Formula VI-F4); C is the width of the footing toe, in feet; Dt is the depth of the soil above the floodwall toe, in feet; Wsh is the weight of the soil over the heel, in pounds, (Formula VL-F5); Ah is the width of the footing heel, in feet; WWh is the weight of the water above the heel, in pounds, (Formula VI-F6); and Fp is the passive saturated soil force over the toe, in pounds (Formula VI-F 12). (Refer to Figure V I-F1 7) Formula VI-F16: Sum of Resisting Moments VI-F.30 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Januarv 1995 Design 3. Factor of Safety Against Overturning: As mentioned earlier, for a stable condition, the sum of resisting moments, MR should be larger than the sum of the overturning moments, Mo, resulting in a factor of safety greater than 1.0. However, the factor of safety against overturning, FS(OT),should not be less than 1.5. If FS(OT)is found to be less than 1.5, the designer should increase the footing dimensions, then go back to Step 3 and try again (see the flow chart for design of floodwall). I= DI Inca 0, FS(OT)=MR/MO= _ 1.5 where: FS(OT) is the factor of safety against overturning (should be greater than 1.5); MR is the sum of the resisting moments, in foot-lbs, (Formula VIF15); and MO is the sum of the overturning moments, in foot-lbs, (Formula VI-F 1 6). Formula VI-F17: Factor of Safety Against Overturning Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.31 January 1995 Chapter VI: General Design Practices Floodwalls Step 6: Calculate eccentricity. The final resultant of all the forces acting on the wall and its footing is a force acting at a distance, e, from the centerline of the footing. This distance, e, is known as eccentricity. The calculation of eccentricity is important to ensure that the bottom of the footing is not in tension. The eccentricity value is also needed for the calculation of soil pressures in Step 7. The eccentricity, e, is calculated as: e= (BI/2)-((MR -MO)/F) = feet where: e is the eccentricity, in feet; B is the width of the footing, in feet; FV is the net vertical force acting on the footing, in pounds, (Formula VI-F8); MO is the overturning moment, in foot-lbs, (Formula VI-F15); and MR is the resisting moment, in footlbs, (Formula VI-F 16). (Refer to Figure VI-F17) FormulaVI-F18: Eccentricity This eccentricity, e, should be less than 1/6 of the footing width. If e is found to exceed B/6, then change the footing dimensions, go back to Step 3, and try again (see flow chart for design of floodwall). VI -F.32 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Step 7: Calculate soil pressures. The soil pressures, q, are determined from the following formula. 001j q = (FV/B)(1± (6e/B)) = lbs/ft2 where: q is the soil pressure created by the forces acting on the wall, in pounds per square foot; Fv is the net vertical force acting on the footing, in pounds, (Formula VI-F8); B is the width of the footing, in feet; and e is the eccentricity, in feet (Formula VI-F 18). (Refer to Figure VI-F17) Formula VI-F19: Soil Pressure The maximum value of q should not exceed the allowable soil bearing capacity. The bearing capacity of soil varies with the type of soil, moisture content, temperature, and other soil properties. The allowable values should be determined by a geotechnicalengineer. Some conservative allowable bearing values for a few soil types are given in Table VI-Fl Soil Factors for Floodwall Design. If the computed value of q is more than the allowable soil bearing value, increase the footing size, then go back to Step 3 and try again (see flow chart for design of the floodwall). Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.33 January 1995 Chapter VI: General Design Practices Floodwalls -t The bending moment (Mb) for sizing reinforcing steel in the vertical floodwall component is the product of the lateral hydrostatic force (FH) and the distance between the point of force application and the bottom of the vertical floodwall component (H/3 -ta.) Step 8: Select reinforcing steel. Select an appropriate reinforcing steel size and spacing to resist the expected bending moment, Mb. Figure VIF18 illustrates a typical floodwall reinforcing steel installation. The cross-sectional area of steel reinforcing required can be computed using Formula VI-F20. This formula assumes use of steel with a F = 60 ksi. N I0E a Mb A-= 1000 = in2/one-footwidth ofwall 1.76df where: A, Mb 1000 df is the cross-sectional area of reinforcing steel required per foot width of wall, in square inches; is the bending moment, in footlbs; is a factor used to convert foot- pounds to foot-kips; and is the distance between the reinforcing steel and the floodwall face opposite retained material, in inches. (Refer to Figure Vl-F 18) Formula VI-F20: Cross-Sectional Area of Steel s VI -F.34 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design d, is typically the floodwall thickness minus 3-1/2" to allow a minimum of 3" between the reinforcing steel and the floodwall edge. The selection of reinforcing steel in the footing portion of a floodwall is computed using Formula VI-F20 while modifying Mb for top and bottom steel considerations. For top steel, the moment is the product of the weight of soil and water over the heel (wsh+wvh) and the heel length (Ah) divided by 2. The selection of bottom steel is a function of the soil bearing pressure. The moment can be computed by adding the soil bearing pressure at the toe edge of the vertical floodwall section to twice the maximum soil bearing pressure (q + 2q,,,) and multiplying this sum by toe length squared over 6 (C2/6). The soil bearing pressure at the toe edge of the vertical floodwall section (q) can be computed by ratio from the calculations (for q.., qma)shown in step 7. Using the computed cross-sectional area of reinforcing steel, refer to ACI to select the most appropriate steel reinforcing bar sizeand spacing. ..aII. Figure VI-F 18: Typical Reinforcing Steel Configuration Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.35 January 1995 Chapter VI: General Design Practices Floodwall Sample Calculation [ FLOODWALL SAMPLE DESIGN Objective: Design a cantilever floodwall to protect a residence subject to 3 feet of flooding. Site soil conditions are as follows: Clean Dense Sand, Unit Weight = 120lbs/ft3; Allowable Soil Bearing Capacity = 2,000 lbs/ft2;Equivalent Fluid Pressureof Soil = 78 lbs/ft3; Coefficient of Friction (Cf)= 0.47; Passive Soil Pressure (k) = 3.69; and Cohesion = 0. The floodwall is in an area of potential normal impact loading and expected flood velocities are 5 fps. Step 1: Assume wall height and footing depth (refer to Figure VI-F 17). H = 7.0 feet D = 4.0 feet Dh = 5.0 feet tfg = 1.0 feet Step 2: Determine dimensions (refer to Figure VI-F17). B = 5.0 feet Ah = 2.5 feet C = 1.5 feet twalt 1.0 feet . Wall and footing to be reinforced concrete having unit weight of 150lbs/ft3 1 of 6 VI -F.36 Enaineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Desian Floodwall Sample Calculation Step 3: Calculate forces. DetermineLateral Forces: Formula IV-4 Fh = 1/2(62.4)(7)(7) = 1,528.8 lbs/LF. Formula IV-6 Fdif= 1/2(78-62.4)(5)(5)= 195.0 lbs/LF. Formula IV-9 dh = (1.25)(5)(5)/(2)(32.2) = 0.49 feet. Formula IV-10 Fdh= (62.4)(0.49)(7) = 211.96 lbs/LF. Formula IV-14 Fj= (1,000)(5)/(32.2)(1) = 155.28 lbs. Formula IV-9 F H= 1,528.80+195.00+211.96=1,935.76 lbsALF. Since Fnacts only at a single point, we will not include loading into the uniform lateral floodwall loading. Once the floodwall is sized, we will evaluate the wall perpendicular to flow to determine ability to resist the impact loading. If necessary this wall will be rede signed to resist impact loads. This process will avoid overdesigning of the entire flood wall. FormulaVI-F12 Fp = 1/2(3.69(120-62.4)+ 62.4)(4)(4) = 2,199.55 lbs/LF. Determine Vertical Forces: Formula VI-F1 Fbi = 1/2(62.4)(5)(7) = 1,092.00 lbs. Formula VI-F1 Fb2 = 1/2(62.4)(5)(4) = 624.00 lbs. Formula VI-F1 Fb = 1,092 + 624 = 1,716.00 lbs. Formula VI-F2 WW.11= (7-1)(1)(150) = 900.00 lbs. FormulaVI-F3 Wftg= (5)(1)(150) = 750.00 lbs. FormulaVI-F4 W= (2)(5-1)(120-62.4) = 720.00 lbs. FormulaVI-F5 WSh= (4)(5-1)(120-62.4) = 921.60 lbs. FormulaVI-F6 WWh = (2.5)(7-1)(62.4) = 936.00 lbs. Formula VI-F7 WG = 900 + 750 + 576 + 540 + 936 = 3,702.00 lbs. Formula VI-F8 Fv = 3,702.00 -1,716.00 = 1,986.00 lbs. 2 of 6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.37 January 1995 Chapter VI: General Design Practices e Floodwall Sample Calculation ( Step 4: Check sliding. Formula VI-F10 Ffr=0.47(1,986) = 933.42 lbs. Formula VI-F13 FR=933.42 + 2,199.55 = 3,132.97 lbs. Formula VI-F14 FS(SL)= 3,132.97/1935.76 = 1.62. OK for sliding since 1.62 > 1.5 (recommended) Step 5: Check overturning. Formula VI-F15 MO= (1,935.76)(7/3) + (195)(5/3) + (1,092)(1013)+ (624)(5/3) + (211.96)(7/2) = 9,314.05 foot-lbs. FormulaVI-F16 MR= (900)(1.5(1/2)) + (750.00)(5/2) + (540)(1.5/2) + (576)(5-(2.5/2) + (936)(5-(2.5/2)) + (2,199.55)(4/3) = 12,682.74 foot-lbs. Formula VI-F17 FS(OT)=12,682.74/9,314.05 = 1.36. No good. Try increasing the footing size to overcome the overturning momement. Assume B = 7.0 feet; Ah = 4.0 feet; and C = 2.0 feet. This requires revision of Steps 3 and 4 for which the results are shown below. FhWF Fdh FH FP,Wwallwill not change. Recom pute vertical forces. FormulaVI-F1 F = 1/2(62.4)(7)(7) = i,528.80 lbs. FormulaVI-F1 Fb2 = 1/2(62.4)(7)(4) = 873.60 lbs. FormulaVI-F1 F= 1,528.80+ 873.60 = 2,402.40 lbs. Formula VI-F2 Ww,,l = (7-1)(1)(150) = 900.00 lbs. Formula VI-F3 Wf = (7)(1)(150) = 1,050.00 lbs. Formula VI-F4 W, = (2)(5-1)(120-62.4) = 720.00 lbs. Formula VI-FS W h= (4)(5-1)(120-62.4) = 921.60 lbs. 3 of 6 VI-F.38 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Floodwall Sample Calculation Formula VI-F6 Formula VI-F7 Formula VI-F8 Recheck Sliding Formula VI-F10 FormulaVI-F13 Formula VI-F14 Recheck Overturning Formula VI-F15 Formula VI-F16 Formula VI-F17 Step 6: Determine eccentricity. Formula VI-F18 WWh = (4)(7-1)(62.4) = 1,497.60 lbs. WG= 900.00 + 1,050.00 + 921.60 + 720.00 + 1,497.60 = 5,089.20 lbs. F, = 5,089.20 -2,402.40 = 2,686.80 lbs. Ffr = 0.47(2,686.80) = 1,262.80 lbs. FR = 1,262.80 + 2,199.55 = 3,462.35 lbs. FS(SL) =3,462.35/1,935.76 = 1.79. OK for sliding. MO = (1,528.80)(7/3) + (195)(5/3) + (1,528.80)(2(7)/3) + (873.60)(7/3) + (211.96)(7/2) = 13,806.85 foot-lbs. MR = (900)(2t(1/2)) + (1,050.00)(7/2) + (720)(2/2) + (921.60)(7-(4/2)) + (1,497.60)(7-(4/2)) + (2,199.55)(4/3) = 21,673.74 foot-lbs. FS(OT)= 21,673.74/13,806.85 = 1.57 OK for overturning since 1.57 > 1.5 (recommended) e = 7/2 -(21,673.74 -13,806.85)/2,686.80 = 0.57 < 7/6 OK 4 of 6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.39 January 1995 Chapter VI: General Design Practices Floodwall Sample Calculation Step 7: Check soil pressures. Formula VI-F19 q = (2,686.80/7)(1 ± 6(.57)/7))) q..= (2,686.80/7)(1 -(6(.57)/(7))) = 195.64 lbs/ft2 qmx= (2,686.80/7)(l+(6(.57)/(7))) = 572.64 lbs/ft2 < 2,000 OK Step 8: Select reinforcing steel. For steel in the vertical floodwall section: Formula VI-F20 A, = (1935.76)(7/3-1)/1000/(1.76)(8.5) = 0.17 in2 For top steel in the footing section: Formula VI-F20 As = ((921.60 + 936.00)(2.5)/2)/1000/ (1.76)(8.5) = 0.13 in2 For bottom steel in the footing section: ratio q from q.jn' qmg1 q = 572.64 -(1.5/8)(572.64-195.64) = 501.95 lbs/ft2 Formula VI-F20 As = ((1.5)2/6)(501.95+ 2(572.64))/1000/ (1.76)(8.5) = 0.04 in2 From American Concrete Institute Reinforced Concrete Design Handbook Table 9a: use #4 bars on 14 inch centers in the vertical floodwall section, use #4 bars on 18 inch centers for the top steel in the footing section, and use #2 bars on 12 inch centers for the botom steel in the footing section. Other ACI documents have similar information. 5 of 6 j VI -F.40 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Floodwall Sample Calculation Since this floodwall design situation also includes normal impact forces, we must check the wall perpendicular to the flow for this loading situation. However, since impact loads do not act uniformly along the wall, the factor of safety of sliding/overturning can be lowered as long as it is above 1.0. This check will change only FH'MO, FS(SL) FS(o0 , and e. Formula IV-14 F. = (1,000)(5)/(32.2)(1) = 155.28 lbs. Formula IV-9 FH = 1,528.80+ 195.00+211.96+ 155.28= 2,091.04 lbsILF. Formula VI-F14 FS(SL)= 3,462.35/2,091.04 = 1.65. OK for sliding since 1.65 > 1.0 (recommended) Formula VI-F15 MO = (1,528.80)(7/3) + (195)(5/3) + (1,528.80)(2(7)/3) + (873.60)(7/3) + (211.96)(7/2) + (155.28)(7) = 14,893.81 foot-lbs Formula VI-F17 FS(OT)= 21,673.74/14,893.81 = 1.45 OK for overturning since 1.45 > 1.0 (recommended) Formula VI-F18 e = 7/2 -(21,673.74 -14,893.81)/2,686.80 = 0.97 < 7/6 OK OK for eccentricity. Therefore the wall as designed will withstand the anticipated impact loading. If the factors of safety for overturning/sliding and the eccentricity had not been acceptable, the footing should be resized or enlarged (B, Ah, and C). 6 of 6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.41 January 1995 Chapter VI: General Design Practices Floodwalls FLOODWALLDESIGN -SIMPLIFIED APPROACH This simplified approach uses The following Table VI-F3 presents general factors used in assumed site conditions. The designer should be aware that the developig a standardized approach to floodwal design. If previous process is normally used the soil conditions at the site in question do not reflect the in the design of most floodwalls. assumed conditions below, the standard criteria approach However, this design process can cannot be utilized, and the detailed design process pre- be shortened for floodwalls of less sented earlier in this section must be used. than three feet in height by assuming certain site-specific soil conditions and design parameters. Based on the stability requirements (assuming no cohe- Presented later in this section is a sion), footing dimensions for various wall heights, footing table of typical floodwall design sizes r .anfloremen s esi depths, and two different soil types have been calculated. sizes and reinforcement schemes that would be applicable in certain The calculation results are shown in Tables VI-F4 and VI- situations. The designer should be F5. The designer can utilize the followingtablesto specify awarethat unless the situationin floodwall/footing dimensions required for heights up to 7.0 aquestion meets the assumptions feet, which reflect flooding levels from 1.0to 4.0 feet andstandarddesign criteria minimum of three feet of soil over the established herein, it would be (icludig a footing). prudentto completethe entire Flooding levels can be computed as (H -Di). It is impor designprocessfor the floodwall tant to note that these dimensions are very conservative and application. the designer may be able to reduce the dimensions. VI -F.42 Enaineerina Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design In these calculations, the following assumptions have been made: 1-Wall and footing are of concrete 2 -Wall thickness = F -0" 3 -Footing thickness = 1' -0" 4 -Minimal debris impact potential 5 -Minimal velocity (<5fps) 6 -Reinforcing consisting of #4 steel bars on 12-inch centers in both the wall and footing Table VI-F2 Assume d Soil Factors for Simplified Floodwall Design Allowable kP Equivalent Fluid Soil Type ure,Bearing Press Ibs./ft.2 Passive Soil Pressure Coefficient C, Friction Factor Pressure for Saturated Soil Unit Weight of Soil lbs/R3 Clean, dense sand and gravel 2,000 3.70 0.55 75 120 GW, GP, SW, SP Dirty sand and gravel of restricted permeability 2,000 3.00 0.45 77 115 GM, GM-GP, SM, SM-SP Engineering Principles and Practice s of Retrofitting Flood-Prone Residential Structures Vi -F.43 January 1995 Chapter VI: General Design Practices Floodwalls Table VI-F3 Typical Floodwall Dimensions for Clean, Dense, I Sand and Gravel Soil Types: (GW. GP, SW, SP) 1 Height of Depth of Depth of Base Width* Heel Width* Toe Width* Floodwayl* Soil on Soil on B (ft) Ah(ft) C (ft) H (fIt) Water Land* Side Dh (ft) Side D,(ft) 41'-oi 31-o0l 3 -O3i 2' -6" 1'-0" 6 51 -0t 31 -311 31-OQi 41-6"t 2'-6"1 1t-Oi 41'-0" 31-4'-2'-Oil 1by- 0" Oil O" 41 -Ol 41-Oil 41-61" 21 -6" 1'3-O1 61-O" 31-3' -0" 6'-6" 31-61" 2' -0" 41-011 31-3"l 61 -0" 3' -611 11 -611 59-QiI 31 -0l 51-6" 3' -0"1 11 -61" 41-Oil 4' -O" 41-6" 2' -6" 1' Oil 51 -Oil 41 -Ot 41-Oil 2'-6" 6" 71-Oil 31 -Oil 39 -Oil 91 -3tt 6' -6"' it -6"1 70 3' 41-0" 3-0" 71 0"l 3-6" 21'-6" 59 -Oi 4 -0" 6' -6" 31 -611 21 -0" 45-31-0" " 53-" 2' -0" 4'-8'6'- 0"1 31 -Ot 71-Q" 41-6" 1'- 6" 61-0" 4.-0" 6' -O11 3' -69 1 -6" *Refer to Figure VI-FI 7 VI -F.44 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Table VI-F4 Typical Floodwall Dimensions for Dirty Sand and Gravel of Restricted Permeability Soil Types: (GM, GM-GP, SM, SM-SP) Depth Depth Height of of Soil on of Soil on Base Width* Heel Width* Toe Width* Floodwall* Heel* Toe* B (ft) Ah (ft) C (ft) H (ft) Dh (ft) Dt (ft) 4'-i 3' -0i" 39-0I" 2'-61" 11- Oi 0'-6" 51 -0t 31-0i 3' -0" 5' -0" 2' -6" 1'-6" 41 -Ott 39 -oil 41 -612' -6 1 ' -0" 4' -Of 4' -Of$ 49-Ot 2' -0" 1'-0" 61 -0" 31-Ot 31-0i 8' -Olt 5' -6" 1i'-6" 4' -Of 39-0i" 7-6" 5' -61" 1'-0" 5'-Oit 3'-Off 7'-Off 5'-6"O -611 41 -Ol 41 -Ol 59 -6"1 31 -0i 11 -6"1 5' -Of 4' -Qil 5' -Of 31-oi 1 -6" 7'- 0 4' -Of 4'-0" 8'-0'' 5'- 0 2'-0" 51-opt 41-Of' 7' -Olt 49-oi 2' -0 6' -Ol 41 -0i 6' -6" 49-0i" 1' -5"9 *Refer to Figure Vl-F1 7 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.45 January 1995 Chapter VI: General Design Practices > y > Floodwalls FLOODWALL APPURTENANCES Floodwall appurtenances include drainage systems, stair details, wall facings, patios, existing structure connections (sealants), existing structure support (posts and columns), and closure details. Each will be discussed with illustra tions, details, and photographs provided to help the de signer develop details that meet the needs of their specific situation. The designer is reminded that it is likely that a local building code may have standards for the design and construction of many of these items. Floodwall Closures In designing floodwall closures, many of the principles discussed earlier in the dry floodproofing section apply. Watertight closures must be provided for all access openings such as driveways, stairs, and ramps, and seals should be provided for all utility penetrations. Figure VI-F19 illustrates typical floodwall closures. Structural analysis for the design of closures should follow the procedures outlined previously for shield design. VI -F.46 Engineerina Principlesand Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Water Latching Dogs Are Commonly Used To Secure a Closure Panel. Water Side-Hinged Closure Track Drop-In Closure Figure VI-F 19: Typical Floodwall Closures Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.47 January 1995 Chapter VI: General Design Practices Floodwalls 0////z///,X//7,//// /~ Free I . I Width of Opening 0:Th I. .. Supporte I I . Closure I .,Supported I. .. I. ..I. ,1.'. --. . .I -. -. t Bottom of Opening Supported or Sealed W1-I Figure VI-F20: Closure Variables The type of closure used depends primarily on the size of the opening that needs to be protected. This will determine the type of material to be used and how the closure is to be constructed and operated. Longer and larger closures, such as for a driveway, must be able to withstand significant flood forces, and therefore should be made of a substantial material. Normally this would be steel plate, protected against rust and corrosion. Heavy aluminum plate may also be used, although it will likely need to be reinforced. In either case, due to the weight of the closure, it is usually best that it be hinged so that it can swing into place. Hinging can be located along the bottom so the closure lies flat when not in use, or it can be placed along one side, so the closure can fold back out of the way. For normal passage openings, aluminum is probably the most common material used. It is a lightweight material, allowing for easy fabrication and transport, and it is resistant to corrosion. Aluminum can buckle under heavy water pressure, so it may need some additional reinforcement. VI -F.48 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design For smaller openings, exterior grade plywood is also commonly used. It is relatively inexpensive and is easily fabricated. However, plywood is subject to warping if not properly stored. In addition, it will collapse under relatively low flood forces, and will usually require significant reinforcement, usually some type of wood frame. Aluminum and plywood are both light enough to be used for temporary closures that can normally be stored in a safe location and installed only when floodwaters threaten. There are many different arrangements that can be used to install these movable closures. The more common methods include the "drop-in" shield that fits into a special slot arrangement and the "bolt-on" shield that is affixed over an opening. There are several different types of hardware that can be used to secure a closure in place, such as T-bolts, wing nuts on anchored bolts, or latching dogs. It is absolutely essential that closures be made watertight. This is normally accomplished through the use of some type of gasket. Neoprene and rubber are materials com monly used, but there are a number of other materials readily available that perform equally as well. The successful performance of a closure system also requires that it be held firmly against the opening being protected. Although the hydrostatic pressure of the water may help to hold the closure in place, floodwater surges can result in negative pressure that can pull off an improperly installed closure. Whatever material is used, it must be of sufficient strength and thickness to resist bending and deflection failures. The ability of a specific material to withstand bending stresses may be substantially different from its ability to withstand deflection stresses. Therefore, to provide for an adequate factor of safety, the required closure thickness should be calculated twice: first taking into account bending stresses, and second taking into account deflection stresses. The resulting thicknesses should be compared and the larger value specified in the final closure design. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.49 Januarv 1995 Chapter VI: General Design Practices Floodwalls Orientation of Openings: It is highly recommended that openings in floodwalls and levees nQl be placed on the upstream side. In the event that they are, Formulas VI-F21, VI-F22, VIF23 and VI-F25 should be modified to include the expected hydrodynamic forces. Closures should not be used on upstream sides where impact loads are expected. One method of determining the thickness of the closure for steel and aluminum is presented in Formulas for Stress and Strainby Roark and Young. For a flat plate supported on three sides, the plate thickness required due to bending stresses may be determined by the following formula: t = |Ph + (PdjorPd) c -inches Maxac where: t plate thickness; Ph hydrostatic pressure due to standing water, in psi from Formula IV-4; We width of closure, in inches Max cr allowable stress for the plate material (from material handbooks), in psi; and 13 moment coefficient from Table VI-F5; Pdhand Pd are defined in Formulas IV-10 and IV-12. Formula VI-F21: Plate Thickness due to Bending Stresses Similarly, for a steel or aluminum flat plate supported on three sides, the plate thickness required due to deflection stresses may be determined by the following formula: PE_ ECt= (Pdh orPd)Wc inches 1 Ph + E= where: oc deflection coefficient from Table VI-F5; and E modulus of elasticity for the plate material (from material handbooks) in psi. Formula VI-F22: Plate Thickness due to Deflection Stresses VI -F.50 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Januarv1995 Design The variables used in the above equations for plate thickness are illustrated in Figure VI-F20. Table VI-F5, Moment Coefficients details the moment and deflection coefficients as a function of the ratio of plate height to width. Table VI-F5 Moment (P3) and Deflection (a) Coefficients hjWcI 0.05 0.67 1.00 1.50 2.00 2.50 3.00 3.50 4.00 a 0.11 0.16 0.20 0.28 0.32 0.35 0.36 0.37 0.37 13 0.03 0.03 0.04 0.05 0.06 0.06 0.07 0.07 0.07 *See Figure VI-F19 Allowable values for carand E may be found for steel plates in Manual of Steel Construction, American Institute of Steel Construction, and for aluminum plates in Aluminum Construction Manual, the Aluminum Association. The method of designing plywood closure plates is similar to that for steel and aluminum closure plates except that the varying structural properties of plywood make using a single formula inappropriate. Because these structural properties are dependent upon the grades of plywood sheet, the type of glue used, and the direction of stress in relation to the grain, determination of the thickness and grade required for a plywood closure is best achieved by assuming a thickness and grade of plywood and calculating its ability to withstand bending, shear, and deflection stresses. This involves calculating the actual bending, shear, and deflection stresses in the plywood closure plate for the thickness and grade specified. These actual stress values are then compared with the maximum allowable bending, shear, and deflection stresses (taken from APA Plywood Design Specifications). If the actual stresses computed are less than the maximum allowable stresses for bending, shear, and deflection, then the thickness and grade specified are acceptable for that application. However, if either of the actual bending or Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.51 Jlamnlni 1QQ.9; Chapter VI: General Design Practices Floodwalls shear stresses or deflection exceeds the maximum allowable values, the closure plate is not acceptable and a new 6 The designer is referred to Plywood Design Specifications, American Plywood Association, for a detailed discussion of design guidelines. thickness and/or grade of plywood closure plate should be specified and the calculations repeated until all actual stresses are less than the maximum allowed. The following guidance has been prepared to illustrate one method of designing plywood closure plates. Note that a one-way horizontal span is assumed because the variability of plywood properties is dependent upon grain and stress direction. Compute bending moment on horizontal one-way span (supported on two sides only). a ME Mb= Ph + (dhr Pd ))We2 = in-lbs/in 8 where: Mb is the bending moment in in-lbs/in; Ph is the hydrostatic pressure due to standing water, in psi from Formula IV-4; We is the width of the closure in inches; and Pdh an( d Pd are defined in Formulas IV-lO and IV-12. Formula VI-F23: Bending Moment Check bending stress. Mt,_ ~KS ' where: fb is the bending stress in psi; Mb is the bending moment in in-lbs/in; and KS is the effective section modulus from a reference in in3/in. Formula VI-F24: Bending Stress VI -F.52 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design If the calculated bending stress for the specified plate (Qb)is less than the maximum bending stress allowed (Fb)(from references), the closure plate is adequately designed for bending applications. If not, the closure should be redesigned and the calculation repeated. Compute shear force. l vs (Ph+(PdhorPd))WC _ pounds2 where: V5 is the shear force in pounds; Ph is the hydrostatic force in psi Formula IV-4; WC is the width of the closure plate in inches; and PA an(I Pd are defined in Formulas IV- 10 and IV-12. Formula VI-F25: Shear Force Check shear stress. __~~~v CRS _ pounds where: f is the shear stress in pounds; and CRS is the rolling shear constant dimensionless. Formula VI-F26: Shear Stress If the calculated shear stress for the specified plate (f5) is less than the maximum shear stress allowed (F), the closure plate is adequately designed for shear applications. If not, the closure should be redesigned and the calculations repeated. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.53 January 1995 Chapter VI: General Design Practices Floodwalls -0 Compute deflection for a single one-way span. I II I A= Pdhor Pd))(W}C 4 i_(PIh,( +y) I b 921.6(E)(I) -inches where: Ab is the computed deflection in inches; Ph is the hydrostatic pressure, in psi. from Formula IV-4; WC is the unsupported width in inches; y is a support width factor in inches; E is the Modulus of Elasticity in psi; I is the Effective Moment of Inertia in in4/ft; and Pdhand Pd are defined in Formulas IV-lO and IV-12. Formula VI-F27: Plate Deflection for a One-Way Span Check deflection. A customary and acceptable level of deflection may be expressed as | E ~~Ab(allowable)= 24¢ = _ inches where: Ab is the allowable deflection in inches; and WC is the unsupported width in inches. Formula VI-F28: Allowable Deflection VI -F.54 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design If the calculated deflection (Ab) is less than the allowable deflection (Ab), the closure plate is adequately designed for deflection situations. If not, the closure should be redesigned and the calculations repeated. Closure plates of plywood are limited to short spans and low water heights. It should also be noted that most plywood will deteriorate when exposed to high moisture. Therefore, plywood closure plates should be examined periodically and replaced as necessary. Drainage Systems When designing a floodwall system, the designer must verify that it will not cause the flooding of adjacent property by blocking normal drainage. Specific information and local requirements can be obtained from the local zoning commission, the building inspector, or the water control board. Before deciding on a design, the designer should check local building codes, floodplain and/or stormwater management ordinances, zoning ordinances, or property convenents that may prohibit or restrict the type of wall planned. The flood protection design should be developed to divert both floodwater and normal rainfall away from the structure. By directing the floodwater and rainfall away from the structure, the designer can minimize potential erosion, scour, impacts, and water ponding. Typical design provisions include: * Regrading the site * Sloping applications * Drainage system(s) =nninagrinn Prinninlaim anrd PracticesQ of PatrnfittinmFlond-Prone Residential Structures VI -F.55 iftna mloi, I 00O. Chapter VI: General Design Practices Floodwalls Regrading the site basically involves contouring. The surface can be contoured to improve the drainage and minimize floodwater turbulence. Ground covers or grasses, especially those with fibrous root systems, can be effective in holding soil against erosion and scour effects of floodwa ters. Sloping applications include providing a positive drainage for engineered applications such as patios, sidewalks and driveways. The material is slightly inclined, typically at a 1% to 2% grade, to an area designed for collection, which includes inlets, ditches, or an existing storm drain pipe system. Figures VI-F21 and VI-F22 show two patio drainage options, and Figure VI-F23 shows a floor drain section typically used to provide positive drainage for patio areas enclosed by floodwalls. These configurations can also be used with sump and sump pump installations. 0 Sample Patio Gravity Drainage Stairs |Stairs Figure VI-F21: Sample Patio Drainage to an Outlet VI-F.56 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Sample Patio Sump Pump Drainage Splash Blbcks Figure VI-F22: Sample Patio Drainage to a Sump Typical Gravity Floor Drain Section Through Floodwall Gatv. Wre Mesh Rodent Scrn w/1/4 Square OpenNt Cut to MatchGrad. // Figure VI-F23: Typical Gravity Floor Drain Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI-F.57 January 1995 Chapter VI: General Design Practices Floodwalls Figure VI-F24: Typical Patio Sump Pump Installation Figure VI-F25: Typical Patio Gravity Floor Drain Installation Drainage systems are a series of pipes that collect and route interior drainage to a designated outfall. Usually the drainage operation is underground and works through a gravity process. However, when grading and sloping will not allow the gravity system to function, provisions for a pumping method, such as a sump pump, should be made. Information on the design of sumps and sump pump applications is provided in the Dry Floodproofing section of this chapter. VI -F.58 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures lanioanr IQQ4; Design For example, in its simplified form, a gutter and downspout outlet, which can be found on almost all houses, is a type of storm drainage system. Provisions at the downspout outfall should also be developed in the site drainage design. Included in the drainage system application is a backflow valve. The unit, sometimes referred to as a check valve, is a type of valve that allows water to flow one way but automatically closes when water attempts to flow in the opposite direction. Figure VI-F26 shows a typical floodwall with a check valve for gravity drainage. The elevation of the drain outlet should be as high as possible to delay activating the backflow valve, while maintaining a minimum of 2% slope on the drain pipe. Typical Floodwall with Check Valve FloodLevel 1 x b a ,Concrete or Block Wall Cast-in Place or Grout 0 Flap Valve -AdM7 Concrete Splash Block C sh B _ />--Zigoncretef Sp~~~~~lash Block Concrete Footing Figure VI-F26: Typical Floodwall With Check Valve The success of the gravity drainage system is predicated on the fact that the floodwater will reach its maximum height after the rainfall at the site has lessened or stopped. Therefore, when the backflow valve is activated, little or no water will accumulate on the patio slab (usually after the rainstorm). However, should this condition not exist, the use of a sump pump and/or design of runoff storage within the enclosed area should be provided. =nrdnaarinn Prinrinaes and Pratices of Rptrnfittinn Flood-Prona RAsidential Structures VI- F.59 January 1 995 / \ Chapter VI: General Design Practices Floodwalls SEEPAGE AND LEAKAGE Floodwalls should be designed and constructed to minimize seepage and leakage during the design flood. Without proper design considerations, floodwalls are susceptible to seepage through the floodwall; seepage under the flood wall; leakage between the floodwall and residence; and leakage through any opening in the floodwall. Seepage Through the Floodwall All expansion and construction joints shall be constructed with appropriate waterstops and joint sealing materials. To prevent excess seepage at the tension zones, the maximum deflection of any structural floor slab or exterior wall shall not exceed 1/500 of its shorter span. Figure VI-F27 illustrates the use of waterstops to prevent seepage through a floodwall. Waterstop Wetted Face- ; Shear Key Waterstop Figure VI-F27: Waterstop VI -F.6O Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Seepage Under the Floodwall The structure design may also include the use of impervious barriers or cutoffs under floodwalls to decrease the potential for the development of full hydrostatic pressures and related seepage. These cutoffs must be connected to the impervious membrane of the building walls to operate effectively. To meet these requirements, it may be necessary to provide impervious cutoffs to prevent seepage beneath the floodwall. This requirement is critical for structures that are designed on highly pervious foundation materials. It may also be necessary to construct a drainage system parallel to the interior base of the floodwall to collect seepage through or under the structure and normal surface runoff from the watershed. All seepage and storm drainage should be diverted to an appropriate number of sumps or gravity drains, or pumped to the floodwater side of the structure. Normal surface runoff (during non-flood conditions) must also be taken into account in the drainage system. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.61 January 1995 Chanter VI: General Desian Practices Floodwalls Leakage Between the Floodwall and Residence 1111111=111M The connection between the existing house wall and the floodwall is normally not a fixed connection, because the floodwall footing is not structurally tied to the house foundation footing. Therefore, a gap or expansion joint The effectivenss of house reasedby may exist between the two structures that offers the poten floodproofing can be inc placing fill against the hc ruseto tial for leakage. This gap should be filled with a water- keep floodwaters from cc oming proof material that will work during seasonal freeze-thaw into direct contact with tl he cycles. structure. One alternative, illustrated in Figure VL-F28, is to utilize a 1/2-inchbituminous expansion material, high-density caulking, and 1/2-inch polyurethene sealant. :-~ VI -F.62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures .1antimmr 1QQ! Design ,,-1/2" Bituminous Expansion Material I 77I1NS1 'o < :.t |00 Concrete Grout Lo 1 ZTwo Alternative Connection Details 1/2" Bituminous Expansion Material -Concrete Grout Figure VI-F28: Floodwall to House Connection ARCHITECTURAL DETAILS Floodwalls can be constructed in a variety of designs and materials. By taking into account the individual house design, topography, and construction materials, and with some imagination, the designer can build a floodwall to not only provide a level of flood protection, but also enhance the appearance of the home. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.63 .laniiarv I Q.A Chapter VI: General Design Practices Floodwalls The floodwall design can be a challenge to landscape or to blend into the terrain. By using natural topography and employing various types of floodproofing techniques, such as waterproofing, sealants, or decorative bricks or blocks, the designer can make a floodwall not only blend in with the house and landscape, but also make an area more attractive by creating a privacy fence or by outlining a patio or garden area. The two most common applications of cosmetic facing of a floodwall consist of brick facing and decorative block facing. This is illustrated in Figure VI-F29. Figure VI-F29: Typical Cosmetic Facings VI -F.64 Enaineerina PrinCiDlesand Practices of Retrofitting Flood-Prone Residential Structures Januarv 1995 Design Typical floodwall design often incorporates the use of a patio, which is enclosed by the floodwall. A concrete slab- on-grade or decorative brick paving can be constructed between the house and the floodwall, which will create an attractive and useful feature. The slab-on-grade or brick paving can serve four very functional purposes: * Patio area for the homeowner; * Additional bracing for the floodwall; * Positive drainage away from the building towards drainage collection points; and * Impervious barrier inside the floodwall to reduce infiltration of water into the soil adjacent to the structure. The patio floor or slab-on-grade is set four inches below the door openings to provide for a reasonable amount of water storage to accommodate rainfall and roof-gutter spillage that may occur after the floodwater has reached the elevation that will have closed the backflow valve on the patio drain. The concrete slab is sloped to a floor drain (or drains) which discharge, if existing grade allows, through a gravity pipe or sump pump installation. In addition to designing patio applications, a qualified design professional can develop architectural and structural modifications that will accommodate existing/future wood decks or roof overhangs (illustrated in Figures VI-F30 and 31). These supports can bear on the floodwall's cap, provided additional structural modifications to the floodwall and foundations are furnished to sustain the increased load from above. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vi -F.65 January 1995 Chapter VI: General Design Practices Floodwalls Typical Floodwall Supporting Columns Wood Column Galv. Post Base 10d Galv. Comm. Nails (4 Total) -'. -1/2" x 12" Galv. Anchor vwith2" Hook and Foundation Loads Figure VI-F30: Floodwall Supporting Columns Figure VI-F3 1: Floodwall Supporting Columns VI-F.66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1 995 Design Residential access requirements, such as driveways, sidewalks, doors, and other entrances, will need to be examined during the design. These entrances may create gaps in the floodwall. Every effort should be made to design passages that extend over the top of the wall and not through it. A stile stairway over a floodwall provides access while not creating an opening in the floodwall. The stile is a series of steps up and over the floodwall and to the designed grades, which thereby closes the floodwall gap and provides a permanent flood protection. Handrails, railings, and stair treads and other safety features must be incorporated into the stile stairway in accordance with local building codes. ypical Step Detail Scale: 3/4" = 1'-0" Varies(See Plans) Atitn Flod-PoneResdenialStu1(Typ Radius ) < < Soo ~~~~~~~Plans_ 3\i7F~~~~~~~~~~1,2' E.J 2 4Mn H Conc. 4, Grae + So Plan^Pns Paio for Figure VI-F32: Typical Step Detail Engineering Principles and Practices of F Retrofitting Flood-Prone Residential Structures VI -F.67 January 1995 Chapter VI: General Design Practices Floodwalls Figure VI-F34: Typical Floodwall Steps In addition to the architectural qualities the floodwall can provide, the entire site area can be finished with landscaping -Vt features such as planter boxes, trees, and shrubs. Vegetative cover and stone aggregate can also be utilized not only to Landscaping inside and enhance the flood protection, but also as a method of erooverchanging a protected area may sion and scour prevention. A qualified landscape architect generate organic debris that could should be consulted when selecting material coverage for a clog drains. Plants should be particular area. Roots, foliage, leaves, and even potential selected that do not result in clogged drains from falling leaves growth patterns of certain trees and shrubs should be ac or fruit. counted for in the selection of landscaping materials. Figure VI-F35 shows a typical landscaping alternative. VI -F.68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Figure VI-F35: Typical Floodwall Landscaping Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.69 January 1995 Chapter VI: General Design Practices Z 9 ~ Floodwalls MAINTENANCE CONSIDERATIONS Once the flood protection has been constructed, a maintenance schedule should be adopted to ensure the system will remain operational during flooding conditions. Floodwalls should be inspected annually for structural integrity. The visual investigation should include a checklist and photographic log of: * Date of inspection * General floodwall observations involving wall cracking (length, width, locations), deteriorated mortar joints, misalignments, chipping, etc. * Sealant observation, including displacement, cracking, and leakage. * Overall general characteristics of the site including water ponding/leakage, drain(s), and drainage and site landscaping. * Operation of the sump pump, generator/battery, and installation of any closures. * Testing of drains and backflow valves Additionally, the entire flood protection system should be inspected after a flood. A complete observation including a photographic record similar to the annual report should be developed and may also include: * damages associated with impacts and flood, * excessive scour and erosion damage, VI -F.70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Maintenance Considerations * floodwater marks, and * functional analysis regarding the flood protection system. The following floodwall inspection worksheet (Figure VIF36) can be used to record observations during the annual and post-flood inspections. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.71 January 1995 Chapter VI: General Design Practices Floodwalls Owner Name: Prepared By: Address: Date: Property Location:_ Floodwall Inspection Worksheet FLOODWALL COMPONENT YES NO OBSERVATIONS Cracking in Wall Mortar Joint Separation _ Wall Misalignment Miscellaneous Chipping & Spalling Possible Leakage Spots Sealant Displacement Water Ponding Drains Functional Sump Pump Operational Landscaping Sketch Area: General Observations and Summary: Figure VI-F36: Floodwall Inspection Worksheet I VI F. 72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Maintenance Considerations CONSTRUCTION During the construction of a floodwall, periodic inspections should be conducted to ensure that the flood protection measure has been built per the original design intent. As a minimum the designer, owner, or owner's representative should inspect and observe the following improvements: e Confirm adequate slope drainage, including drain pipes, patio, and grading outside the floodwall; * Confirm that floodwall foundation was prepared in accordance with plans and specifications; * Confirm that sealants, waterproofing, and caulking were applied per the manufacturer's requirements for installation; * Confirm that the sump pump is operational; * Check sample brick or decorative block (before installation) for patterns or match to existing conditions; and * Confirm that a maintenance requirement checklist was developed and used, which included all of the manufacturer's recommendations for passive flood protection applications, sealants, drains, etc. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -F.73 January 1995 Levees Table of Contents Field Investigation................................................................................................................ I-L.I Design................................................................................................................................ VI-L.4 Standard Criteria ........................................... VI -L.4 Maximum Settled Height of Six Feet ............. .............................. VI -L.4 MinimumCrestWidthofFiveFeet ........................................... VI -L.5 Floodwater Side Slope of 1 Vertical on 2.5 Horizontal ........................................ VI -L.5 Land Side Slope ........................................... VI -L.5 One Foot of Freeboard ........................................... VI -L.5 InitialPhases.................................................................................................................. VI- L.6 Locate Utility Lines That Cross Under the Levee ........................................... VI -L.6 Provide "Cut-Off' for Levee Foundation Seepage ........................................... VI -L.7 Identify Foundation Soil Type ........................................... VI -L.7 Clay Foundation................................................................................................ VI-L.7 Sandy Foundation ........................................... VI -L.7 Seepage Concerns .................. VI -L.8 Scouring/Slope Protection .................. VI -L.9 InteriorDrainage .................. VI -L.10 Maintenance .................. VI -L. 11 Cost .................. VI -L.12 Construction .................. VI -L.14 Soil Suitability .................. VI -L.14 Compaction Requirements .................. VI -L. 14 SettlementAllowance .................. VI -L. 15 Borrow Area Restrictions .................. VI -L.15 Access Across Levee .................. VI -L. 15 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -L.i January 1995 Field Investigation LEVEES Levees are embankments of compacted soil that keep shallow to moderate floodwaters from reaching a structure. A well designed and constructed levee should resist flooding up to the design storm flood elevation, eliminating exposure to potentially damaging hydrostatic and hydrodynamic forces. This chapter outlines the fundamentals of levee design and provides the designer with an empirical design suitable to a limited range of situations. The design criteria outlined in the USACE manual number EM 110-2-1913, entitled Design and Construction ofLevees, are complex and intricate because they must provide for a wide variety of design conditions that are not always applicable to residential levees. These additional factors could result in construction costs that are considerably higher than the value ofthe benefits (damages avoided) associated with construction. If certain design parameters are controlled, the costs should be greatly reduced, allowing the individual homeowner to consider this retrofitting technique an economically feasible option. FIELD INVESTIGATION Certain conditions must exist before levees can be considered a viable retrofitting option. The questions that should be asked before proceeding any further are listed below: Under NFIP regulations, levees are not recognized as acceptable Does the natural topography around the structure in ques- retrofitting measures for new and tion lend itselfto this technique? substantially damaged or improved structures. A significant portion of the cost associated with the construction of a levee hinges upon the amount of fill material needed. If the topography around the structure is such that --... only one or two sides of the structure need to be protected, a levee may be economical. Placement of levees in the floodway is not allowed under local floodplain regulations. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -LA January 1995 Chapter VI: General Design Practices Levees Is a suitable impervious fill material readily available? 6 A suitable impervious fill material, such as a CH, CL, or A settled height of six feet is the SC, as defined in American Society for Testing and maximumelevationrecommended Materials (ASTM) designation D-2487, entitled Classiforindividualresidentiallevees. fication ofSoils, is required to eliminate concerns of seepage and stability. * Do local, state, or federal laws, regulations, or ordinances restrict or prevent the construction of a levee? Coordination with local, state, and federal officials may be necessary to determine if the levee retrofitting option is permissible. Certaincriteriaexistprohibiting construction within a FEMA-designated floodway, the main portion of a stream orwatercourse that conveys flow during a storm. a Will the construction of a levee alter, impede, or redirect the natural flow of floodwaters? Previous calculations from Chapter IV to determine both the depth and velocity of flood flows around the structure in question should be checked to ensure that the levee will not result in increased flood hazards upstream. Also, in many cases the local floodplain administrator may require an analysis ofthe proposed modification to the floodplain. * Will flood velocities allow for the use of this technique? If the flood velocities along the water side of the levee embankment exceed eight feet per second, the cost of protecting against the scour potential may become so great that a different retrofitting technique should be considered. The designer of a levee should be aware that the construction of a levee may not reduce the hydrostatic pressures against a VI -L.2 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Field Investigation below-grade foundation. Seepage underneath a levee and the natural capillarity ofthe soil layer may result in awater level inside the levee that is equal to or above grade. This condition If the assumptions listed in this is worsened by increased depth of flooding outside the levee chapter are not applicable to the and increased flooding duration. Unless this condition is site being considered, an experi- relieved, the effectiveness ofthe levee may be compromised. enced levee designer should be This condition, which involves the intersection ofthe phreatic consulted or another method line with the foundation, is illustrated in Figures VI-FI 1 and VI- considered. F 12. It is important that the designer check the ability ofthe existing foundation to withstand the saturated soil pressures that would develop under this condition. The computations necessary for this determination are provided in Chapter [V. The condition can be relieved by installation of foundation drainage (drainage tile and sump pump) at the footing level, and/or by extending the distance from the foundation to the levee. The land side seepage pressures can also be decreased by placing backfill against the flood side of the levee to extend the point where floodwaters submerge the soil away from the structure, but the effectiveness of this measure depends on the relative characteristics of the soils investigation. The design of foundation drains and sump pumps is presented in Chapter VI Dry Floodproofmg section. An experienced geotechnical engineer should compute the spacing required to obviate the problem. Enaineerina PrinciDles and Practices of Retrofittina Flood-Prone Residential Structures VI -L.3 January 1995 Chapter VI: General Design Practices y Y Ž Levees DESIGN STANDARDCRITERIA The following parameters are established to provide a conservative design while eliminating several steps in the 2V' .JUSACEdesign process, thereby minimizing the design cost. These guidelines pertain to the design and construction of Thesedesign recommendations are localized levees with a maximum settled height of six feet. conservative.Alternativeparam-Techniques of slope stability analysis and calculation of eters for a specific site may be developed by an engineer qualified seepage forces are not addressed. The recommended side in levee design. slopes have been selected, based on experience, to satisfy __________________________ requirements for stability, seepage control, and maintenance. The shear strength of suitable impervious soils compacted to at least 95 percent of the Standard Laboratory density as determined by ASTM Standard D-698 will be adequate to assure stability of such low levees, without the need for laboratory or field testing or calculation of safety factors. The minimum requirements for crest width and levee side slopes are defined below. In combination with the toe drainage trench (which will be defined later in this section) and the cutoff effect provided by the backfilling of the inspection trench, these minimum requirements will provide sufficient control of seepage, and do not require complex analyses. Flatter land side slopes are recommended for a levee on a sand foundation to provide a lower seepage gradient, because a sand foundation is more susceptible to seepage failure than a clay foundation. Maximum Settled Height of Six Feet This is a practical limit placed due to available space and material costs. VI -L.4 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Minimum Crest Width of Five Feet This is required to minimize seepage concerns and allow for ease of construction and maintenance. Floodwater Side Slope of 1 Vertical on 2.5 Horizontal This is required to minimize the scour and erosion potential, to provide adequate stability under all conditions including rapid drawdown situations, and to facilitate maintenance. Land Side Slope The land side slope may vary based upon the soil type used in the levee. If the levee material is clay, a land side slope of one vertical to three horizontal is acceptable. If the levee material is sand, a flatter slope of one vertical to five horizontal is recommended to provide a lower seepage gradient. One Foot of Freeboard This is required to provide a margin of safety against over topping and allow for the effects of wave and wind action. These forces create an additional threat by raising the height of the floodwater. Engineering Principles and Practices of Retrofitting Flood-ProneResidential Structures VI -L.5 January 1995 Chapter VI: General Design Practices Levees | ~~~~~~~~~~mmn. I ~n 'S 2' Figure VI-L 1: Typical Residential Levee INITIALPHASES Because ofthe importance ofthe characteristics of the soil that makes up the levee foundation, the excavation of an inspection trench is required. The minimum dimensions ofthe inspection trench are shown in Figure VIL 1. The inspection trench, which shall run the length of and be located beneath the center of the levee, provides the designer with information that will dictate the subsequent steps inthe design process. The mandatory requirement of an inspection trench is fundamental to the assumptions made for the rest of the design process. The inspection trench will accomplish the following objectives: Locate Utility Lines That Cross Under the Levee Once identified, these must be further excavated and backfilled with a compacted impervious material to prevent development of a seepage path beneath the levee along the lines. VI -L.6 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Design Provide "Cut-Off" for Levee Foundation Seepage The trench itselfwill be backfilled with ahighly impervious soil, such as a CH, CL, or SC, as previously referenced, to create an additional buffer against levee foundation seepage. Identify Foundation Soil Type The construction ofthe inspection trench should provide the designer with a suitable sample to identify the foundation soil type through the use of the Unified Soil Classification System, (USCS). This variable will further direct the design ofthe levee. Clay Foundation If, after inspection, it is determined that the in situ foundation material is composed of a clay soil, as defined by the NRCS, a land side slope of 1 vertical on 3 horizontal should be utilized. Sandy Foundation If, after inspection, it is determined that the in situ foundation is composed of a sandy soil,as definedby theNRCS, a land side slope of 1 vertical on 5 horizontal should be utilized. Fnniniarinn PrinninleQanrd Practices of RetrofittinnFlood-ProneResidential Structures VI -L.7 January 1995 Chapter VI: General Design Practices Z/k ~ cI Levees SEEPAGE CONCERNS Durationoffloodingis a critical consideration in the design of leveeseepagecontrolmeasures. Thelongerthe duration of flooding(i.e.,thelongerfloodwa- tersare in contact with the levee), the greater the potential for seepageandthe greater the need for seepage controlmeasures such as cutoffs, drainage; toes, andimperviouscores. If inspection determines that the Two types of seepage must be considered in the design of a residential levee system: levee foundation seepage and embankment seepage. The amount of seepage will be directly related to the type and density of soils in both the foundation and the embankmentofthelevee. Whiletheinstallationandbackfllling of themispection trench with impervious material willhelp reduce concerns of foundation seepage, further steps must be taken to minimize any embankment seepage for levees between three and six feet in height. The mandatory inclusion of a drainage toe will control the exit of embankment seepage while also controlling seepage in shallow foundation layers. The inclusion of a drainage toe for a levee of varying height will be limited to those areas with a height greater than three feet. If the levee height varies due tothe natural topography, a drainage toe will be required only for those portions of the levee that have a height greater than three feet. foundation consists of a deepThmaoresnfrteicuonfhseesrsiso depositof sandor gravel that will permitseepageunderthe shallow inspectiontrench,a deeper trench wouldbe required, especiallyif basempoentfonedinucur haRsa daefinedsaunde This- or gavl scenariomay make the use of a leveeuneconomical. ffid Long duration floodingmay negatively impact the ability of the drainage toe and inspection trench to control the seepage through and under the levee. Temjrrao o h nlso fteemaue st relieve the pressure of seepage through or under the levee so that piping may be avoided. Piping is the creation of a flowpath for water through or under a soil structure such as a levee, dlarn, or other embankment, resulting in a pipe-like channel carrying water through or under the structure. Piping can lead to levee failure. Piping becomes a more serious problem as the permeability of the foundation soil increases. VI -L.8 Enaineerina Princioles and Practices of Retrofittino Flood-Prone Residential Strimrtiirss January 1995 Seepage Concerns The drainage toe should be sized as shown in Figure VI-L2, and should be filled with sand conforming to the gradation of standard concrete sand as defined by ASTM standards. Figure VI-L2: Drainage Toe Details SCOURINGISLOPE PROTECTION The floodwater side of the levee embanknent may require protection from erosion caused by excessive flow velocities. For flow velocities of up to three feet per second, a vegetatively stabilized or sodded embankment will generally provide adequate erosion protection. Some vegetative covers, such as Bermuda grass, Kentucky bluegrass, and tall Fescue, provide erosion protection from velocities of up to five feet per second. The grasses should be those that are suitable for the local climate. An alternative or supplement to a vegetative cover is the use ofa stone protectionlayer. The layer shouldbe placed onthe entirefloodwaterface ofthe levee and be sizedin accordance with Table VI-L 1: Table Stone Protection Layer VI-Li Guidance VeloctiesMinimum These values are from USACE DiameterofAgainst Slope Manual Design and Construction of Levees. < 2 fps 0.5 inches < 5 fps 2.0 Inches < 8 fps 9.0 Inches . Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VI -L.9 January 1995 Chapter VI: General Design Practices <~Ž Levees INTERIOR DRAINAGE Constructing a levee around a house will not only keep floodwater out, but also will act to keep seepage and rainfall inside the levee unless interior drainage techniques are utilized. One method of draining water that collects from rain and from seepage through and under a levee is to install drainpipes tat Guidanceon estimating interior extend through the levee. While this will allow for drainage by drainagequantitiesis presentedin gravity, the drains must be equipped with flapgates, which close ChapterIV. to prevent flow of floodwaters through the pipe. The flap gates will open automatically when interior floodwaters rise above exterior floodwaters. Normal Conditions River Side, / ~~Levee\ FlapGate0Ope_ _ _ River Flood Conditions Local Drainage Side_ losed- Figure VI-L3: Drain Pipe Extending through Levee To ensure that water from precipitation or seepage within a leveed area is removed during flooding, a sump pump should be installed in the lowest area encompassed by the levee. All interior drainage measures should lead to this.pump, which will discharge the flow up and over the levee. The sump pump should have an independent power source sothat it will stay in operation should there be an interruption of electrical power, a common event during a flood. VI -L.10 Enaineerina Princioles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 FloodwaterSide Slope Top Land Side Slope Top_ FigureVI-L4: InteriorStorage Area Seepage Concerns Analternativeto theuse of a sump pump (for minor storms),is the creation of an interior storage area that will detain all interior flow until the floodwaters can recede. See Figure VI-L4. Typically the storage area is sized for the 2- or 10-year recurrence interval event. Drain Pipe Ponding areas for when flap valves are _ D Drain Pipe MAINTENANCE Levee maintenance should include keeping the vegetation in good condition and preventing the intrusion of any large roots from trees or bushes or animal burrows, since they can create openings or weak paths in the levee through which surface water and seepage can follow, enlarging the openings and causing a piping failure. Planting oftrees and bushes is not permitted on the levee. Any levee design should include a good growth of sod on the top and slopes of the levee to protect against erosion by wind, water, and traffic, and to provide a pleasing appearance. Regular mowing, along with visual inspection several times a year, should identify critical maintenance issues. Pnninaarinn Printcinipq and Pranticesq of Ratrofittino Flood-Prone ResidentialStructures VI -L.11 Januy 1 A gay A--995 --- January 1995 'Chapter VI: General Design Practices Levees COST The accuracy of a cost estimate is directly related to the level of detail in a quantity calculation. The following example provides a list ofthe common expenses associated with the construction of a residential levee. Unit costs vary with location and wholesale price index. To obtain the most accurate unit prices, the designer should consult construction cost publications or local contractors. The designer should also budget an additional five percent ofthe total construction capital outlay annually for maintenance ofthe levee. Table VI-L2, Cost Estimate Example, illustrates the estimated cost (based on 1985prices)for constructionof a three-foothigh, 21 6-foot-long levee, which was built to protect a 1,600SF house in Montgomery County, Maryland. TableVI-L2 Cost Estimate Example Item Cost Strip Topsoil $335.00 Dig Inspection Trench $750.00 Import Fill $1,800.00 Compact Fill $600.00 Riprap $2,700.00 Drain Tile (4" PVC) $215.00 Check Valve $900.00 Sewer Gate Valve $1,200.00 Sump Pump $1,000.00 Discharge Piping $100.00 Total First Cost $9,600.00 VI -L.12 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Table VI-L3 Levee Cost Estimating Owner Name: Address: Property Location: Item Clearing & Grubbing Stripping Topsoil Seeding Sod Import Fill (1 -5 miles) Import Fill (5-15 miles) Import Sand Compact Fill Riprap/Stone Slope Protection Dig Inspection Trench -2' x 4' Drain Gate Valve Drain Check Valve Sump Pump (gasoline, up to 3 h.p.) Sump Pump Generator Sump Pump (gasoline, 3 to 8 h.p.) Drain Tile 4"-6" DIAPVC DrainTile 8"-10" DIA PVC/RCP_ Discharge Piping for Unit T.S. F.* T.S. F.* T.S.F.* T.S.F.* Cubic Yards Cubic Yards Cubic Yards Cubic Yards Cubic Yards _ Linear Feet Each Each Each Each Each Linear Feet LinearFeet Linear Feet Worksheet Prepared By: Date: Unit Cost 1994 Dollars $50.00 to $100.00 $40.00 to $100.00 $30.00 to $40.00 $350.00 to $450.00 $2.50 to $7.00 $7.00 to $21.00 $8.50 to $12.00 $0.75 to $2.00 $25.00 to $35.00 $2.50 to $4.50 $600.00 to $1900.00 $650.00to $1300.00 $850.00 to $1400.00 $350.00 to 1,000.00 $1500.00 to $2250.00 $7.00 to $10.00 I $10.00 to $12.00 $3.00 to $7.00 Seepage Concerns # Units Needed Item Cost (1-2 inch DIA) Sump Pump *T.S.F. = Thousands of Square Feet Total Cost - L7I3 J L | ~~~~~~vI _ _ _ _ _ Engineering Principles and Practicesof Retrofitting Flood-ProneResidential Structures VI -LAO January1995 Chapter VI: General Design Practices Levees CONSTRUCTION To prepare forthe construction of a levee, all ground vegetation and topsoil should be removed over the full footprint of the levee. If sod and topsoil are present, they should be set aside and saved for surfacing the levee when it is finished. SOIL SUITABILITY Most types of soils are suitable for constructing residential levees. The exceptions are very wet, fine-grained, or highly organic soils, defined as OL, MH, CH, OH type soils by the NRCS. The best are those with a high clay content, which are highly impervious. Highly expansive clays should also be avoided because of potential cracking due to shrinkage. COMPACTION REQUIREMENTS As the levee is constructed, it should be built up in layers, or, lifts, each ofwhich must be individually compacted. Each lift should be no more than six inches deep before compaction (see Figure VI-L5). Compaction to at least 95 percent of standard laboratory density should be performed at or near optimum moisture content with pneumatic-tired rollers, sheepfoot rollers,: or other acceptable powered compaction equipment. In some situations, certain types of farm equipment can effect the needed compaction. VI -L.14 EngineeringPrfnciplesand Practices of Retrofitting Flood-Prone Residential Structures January 1995 Construction 6 Settlement allowances vary by geographic region and geologic conditions. Therefore, a five percent allowance may not be applicable in all situations. Consult the state or local floodplain managementofficials for firther information. SETTLEMENT ALLOWANCE The levee should be constructed at least five percent higher than the height desired to allow for soil settlement. BORROW AREA RESTRICTIONS A principle concern for the construction of the levee is the availability of suitable fill for levee construction, but caution should also be taken as to the location of the fill borrow area. For the purpose of this manual a general rule is to avoid utilizing a borrow area within 40 feet of the landward toe of the levee. ACCESS ACROSS LEVEE The complete encirclement of a structure with a levee can create access problems not only for the homeowner but also for emergency vehicles. If the levee is low enough, additional fill material can be added to provide a flat slope in Drine-inidn andi Practirac nf RptrnfittinnFlood-ProneResidential Structures VI -L.1:5 PIi~iii ii~e~ If r 1---A -* A --I -- I'll les… . -- January 1995 Chapter VI: General Design Practices Y I iv! ecl sPU*S . 1W II Qua U UItt Figure VII-4.9: Site Plan: House on Opposite Side of Bailey Creek and Engineering Solutions VI!-62 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1 995 Case #4: Small Levees and Perimeter Floodwalls -_w@.WAI RDNWu WAn 6M ..,- *a MNaAN a~WI a 410=10SIM Figure VII-4.IO: Typical Drain Detail Lev~~~i s 0 SAgo w~~~~a "SVO Al N* W~u. Ala Io ansmoo -. ., Figure VII-4.1 1: Sump Pump and Sur np Detail Engineering Principles and Practices of Ret rofitting Flood-Prone Residential Structures VII -63 January 1995 Chapter VII: Case Studies CASE STUDY #5 Perimeter Floodwall Henson Creek, Prince George's County, Maryland This case involves the construction of a floodwall around the perimeter of a slab-on-grade house located along Henson Creek in Prince George's County, Maryland. The actions taken (sponsored by the Prince George's County, Maryland, Department of Environmental Resources, Watershed Protection Branch) were in keeping with the county's policy to protect houses within the 100-year floodplain and/or remove the threat of flooding to these private residences. The Henson Creek watershed area is a relatively narrow watershed, ranging from 2.5 to 3.0 miles in width and about 11 miles in length. Its combined drainage area, which includes tributary flows, is in the range of about 30 square miles. Various areas along Henson Creek were subject to flooding, and the problems were expected to increase because of development growth within the watershed boundaries. The initial analysis was conducted to examine the feasibility of widening and improving Henson Creek channel for the purpose of flood control. In an effort to remove affected houses from the I 00-year floodplain, five alternative designs were investigated. Four of the studies involved the hydraulic analysis of an existing culvert, and widening and improving the creek's banks. The fifth alternative was to retrofit individual houses. Based on the results of the alternatives evaluated, home retrofitting was the most cost- effective solution to provide 100-year flood protection. The four designs involving culvert structure modification were rejected due to costs that ranged from $1,245,000 to $3,095,000. The retrofitting of individual houses (elevation, floodwalls, wet and dry floodproofing measures) was estimated at $246,800. Retrofitting Methodology DETERMINATION OF FLOOD DEPTH Computer analysis through the use of HEC-2 and TR-20 modeling was used to determine water-surface elevations that would result from a 1 00-year flood based on ultimate watershed development. Cross sections were located at critical locations and at predetermined distances along the stream channel. The flood depth at a particular structure VII -64 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall (residence) was interpolated from the water-surface elevations at the nearest cross section both upstream and downstream. DETERMINATION OF LOW POINT OF FLOODWATER ENTRY Each residence was field surveyed to determine the elevation of all openings into crawlspaces or basements, and ground at the house, first floor, and basement slab. A county engineer reviewed the survey data and determined what elevation the floodwater would have to reach before the residence would begin to flood. Many times this elevation was a vent, an entrance into a crawl space, a walkout from a basement, or the top of a stairwell into a basement. DETERMINATION OF TYPE OF CONSTRUCTION Each residence was reviewed by a team of engineers to determine the type of construction used in the residence. Three types of structures were identified: slab on grade, crawl- space, and full basement. DETERMINATION OF STRUCTURAL COMPETENCE The team of engineers reviewed the construction and condition of each residence to determine if the residence could be successfully retrofitted. DETERMINATION OF RETROFITTING METHOD Each residence was evaluated separately, but structures of similar construction were considered receptive to similar- retrofitting methods. DETERMINATION OF RETROFITTING COSTS The county developed a database of current costs (1988) associated with the retrofitting of residential structures. Personal knowledge and contacts with other individuals in volved in similar work in other jurisdictions as well as cost data from publications includ ing Engineering News-Record (ENR) and Mean 's Guide were used to develop the esti mates. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -65 January 1995 Chapter VII: Case Studies DETERMINATION OF DESIGN CRITERIA The structural analysis of the houses was performed in full accordance with the design requirements set forth in the following codes and regulations: * Prince George 's County Building Code, 1983 * BuildingOfficialsand CodeAdministrators(BOCA)NationalBuilding Code, Ninth ed., 1984 * AmericanStandardBuildingCode Requirementsfor Masonry(ANSI A41.1-1953, Reaffirmed 1970) * Flood-Proofing Regulations (EP 1165 2 314), U.S. Army Corps of Engi- neers, June 1972 In addition, the following references were used as guidelines in the structural computa- tions: * Specificationfor the Design and Constructionof Load-BearingConcrete Masonry (TR75B) National Concrete Masonry Association (NCMA) February, 1987 * Basement and Foundation Walls (TR68-A), NCMA, 1971 * Nonreinforced Concrete Masonry Design Tables (TR03), NCMA, 1971 * Reinforced Concrete Masonry Design Tables (TR84), NCMA, 1971 * DesignManualforRetrofittingFlood-proneResidentialStructures(FEMA 114), Federal Emergency Management Agency, September 1986 * CostReportonNon-StructuralFloodDamageReductionMeasuresfor Residential Building Within the Baltimore District, U.S. Army Engineer Institute for Water Resources, IWR Pamphlet #4, July 1977 VII -66 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall The following design values were used in the structural analysis of the foundation walls: Soil: Soil unit weight = 120pcf Internal friction angle = 30 degrees Active pressure coefficient = 0.33 Masonry: Allowable tension in flexure (normal to bed joints) Type M or S mortar Hollow Units: 23 psi Solid Units: 39 psi Allowable Shear (Type M or S mortar) All Units: 34 psi Compressive Strength, fm = 1,000psi Unit Weight (ASTM C-140) = 120 pcf Allowable stress for grade 60 reinforcing steel, f 24,000 psi S Dead Loads: Floor and Roof: 15 psf Foundation Walls: Density of masonry block = 120 pcf Density of wood: 40 pcf Live Loads: Lateral Earth Pressures: Saturated Soil: 40 psf Water: 62 psf Water plus buoyant soil: 82 psf Wind Pressure: 16 psf Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -67 January 1995 Chapter VII: Case Studies Engineering Analysis Summary Site #1: The site is a one-story, brick veneer over wood-frame slab-on-grade house located south of Henson Creek (see Figure VII-5.1). The first floor elevation (FF) and low point of entry (LPE) is 198.4and the 100-yearwater-surface elevation (WSEL) is 199.0 (see Figure VII-5.2). HENSON CREEK (7%)ROAD r( rm n\\\iI Ig o I Figure VII-5.l: Location Plan VII-68 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall 100 YR. FUTURE V _ ERICKFACEE WOEL 10.09 FINISHED FLOOR ELEV. 106.40 Figure V11-5.2: Preexisting Slab-on-Grade Construction Detail Since the 100-year water surface elevation (WSEL) was only 0.6 feet above the finished floor, the construction of a floodwall around the perimeter of the house proved to be the best option in terms of overall cost (approximately $18,000) and risk to the building. This would allow the house to stand as is and be protected by a separate structural element. The owners were advised of the elevation and/or relocating problems associated with their house and that the county selected the floodwall alternative. The recommendations listed below were developed based on the engineering analysis: * Construct a floodwall around the perimeter of the house. The wall must be at least one foot above the 1 00-year WSEL, or approximately 2.6 feet high to comply with the county code. * Provide at least two step-up/step-down accesses over the wall to the entrances into the house. * Rebuild the concrete patio located in back of the house inside the floodwall. * Provide a gravity drainage system behind the floodwall to rid the ringed area of the trapped water. * Tie down the tool sheds to resist flotation. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -69 January 1995 Chapter VII: Case Studies Proposed Work The proposed work is keyed to Figure VII-5.3, Site Plan. 1. Construct floodwall (see Figure VII-5.4). 2. Construct concrete steps for access over the floodwall (see Figure VII-5.9 and VII-7. 12). 3. Install steel pipe railing. 4. Construct a concrete slab on four-inch gravel base inside the floodwal. Provide positive drainage to sump pump. 5. Relocate telephone junction box vertically to elevation 200.5. 6. Limits of grading, seeding, and mulching. 7. Provide four-inch-high concrete equipment pad under air conditioner, (see Figure VII-5.10). 8. Apply waterproofing between existing wall and topsoil. 9. Install new downspout drain with new coupling through landing. 10. Plant new shrubs. 11. Remove existing concrete pad. 12. Install 6 x 6-inch treated timber retaining wall (see Figure VII-5.9). 13. Fill planter with topsoil. 14. Remove existing concrete slab in its entirety. 15. Furnish and install new sump pump and pit (see Figure VII-5.8). Vll -70 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall - 16. Tie down existing shed. 17. Remove and dispose of fence. 18. Install one-inch round PVC schedule 40 conduit for sump pump electrical cables. 19. Install outside rated double receptacle in 6 x 6-inch exterior lockable box. 20. Verify location of gas line prior to excavation. 21. Limit of disturbance and sod. 22. Provide concrete encasement of three-inch diameter PVC sleeve around existing gas line. Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -71 January 1995 Chapter VII: Case Studies Plans,Elevation, and Construction Details -V 22 3Y STL.hSSYFtVICE, GRt&D -8-7,-6LILAr S. _1. ale1I S-6 LIE.3'1L BxELOW n I9; --.,15 / ;^ t Posr f~~~~~~~~t /"'';' 4 w ; j S4'_A\jI~~~~t' Q .' _ t".tk t _ -S1 I FENC WOOD ELE, TWIN D= T WINDOW SOT. TLOVERt4 4 , J sor i~9DOOR~ ' zs Weaq. WINDOW ist4NEY q. 1 '4 '-4 FIN. FL. EL.-198.4!. ~~~18 ONESTORY2 TX4D' .; /ONESTORY RICKFACESLAB ON GRADE i r NOT.iWINDOW D VENT ROT t WINDOW ASP ~ 201,0 8OT.t9t.4ILOR Jr, ~ / ' _1 / ~~~~~ act~ 9DOOR 220D WN~ _OtW.7 INDOW 139. WdTER 98. ,1i \ 42 4 1CO --r---ON/ 1 AD OZ.N PAD I991 :kV,4 9.2_4 _4 > / 6w R / i I'll It a 710roMAreH ... /MjS/ZOA/ IOU S_ Figure VII-5.3: Site Plan VII -72 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall "@TE: FACESUCKTO UATCH EX. SUCK S JOINTSTOLet UPWM erx1111 TSa 04.O 12csaC C COBoetN 4Ir MAXlt b1 _-4CMU SOP u'i riLA14 *HOW. REINF.A I" CONTINUOUS. an TOM 01*OWA rTnNE. -GROUTINTERIOR SOLID ;WITN4000 PSI PEA GRAVELCONCE ,4_ 4012 Figure VII-5.4: Typical Floodwall Detail Section Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -73 January 1995 Chapter VII: Case Studies Figure VII-5.5: Footer Detail Figure VII-5.6: Wall-to-House Connection Detail VII-74 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall e* 0 * : | | | W~~ Figure VII-5.7: Drain Detail 1.itnaFod-rn Reietal tutrs V-7 Figure VII-5.8: Sump Detail Ennineerinn Princinles and Practices of Reti January 1995 Chapter VII: Case Studies . _ A ___ A.... MIAV Figure VII-5.9: Floodwall Steps and Landscaping Timber Figure VII-5.10: Sump Pump Outlet and Raised Air Conditioner Unit VII-76 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #5: Perimeter Floodwall Figure VII-5.1 1: Completed Project Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -77 January 1995 Chapter VII: Case Studies WET FLOODPROOFING This section presents a case study that identifies procedures, methodology, and design parameters used in wet floodproofing. CASE STUDY #6 Wet Floodproofing a House on a Crawlspace Henson Creek, Prince George's County, Maryland This case study discusses wet floodproofing measures that were taken to protect houses located along Henson Creek in Prince George's County, Maryland. (See Chapter VII, Case #5 for complete background and retrofitting methodology.) Engineering Analysis Summary Site #2: The site is a two-story wood-frame house on a crawlspace with a first-floor (FF) elevation of 199.3 (see Figure VII-6.1). The bottom of the crawlspace vent is 197.5 and the bottom of the crawlspace access door or low point of entry (LPE) is 196.9. The 1 00year water-surface elevation (WSEL) is 198.4 (see Figure VII-6.2). The types of forces imposed by the floodwater will be lateral hydrostatic pressure on the exterior masonry walls and a buoyant force on the first floor timber framing. The house was analyzed under dry floodproofing and wet floodproofing conditions in order to investigate the feasibility of each condition. Figure VII-6.2 is the preexisting foundation wall section. Dry Floodproofing Option On the field inspection, the existing masonry walls appeared to be in good condition; therefore, the mortar joints were assumed to have a structural capacity equal to their capacity at construction. In addition, the calculations are based on the assumption that the bottom of the footing is exactly 30 inches below grade as required by code. The dry floodproofing option was rejected because the analysis showed that the flexural stress in the mortar joints exceeds the allowable stress under 1 00-year flood conditions. Moreover, dry floodproofing would be difficult to achieve since the soil around the VII -78 Engineering Principles and Practices of Retrofittina Flood-Prone Residential Structures January 1995 Case #6: Wet Floodproofing foundation was relatively permeable sandy soil and would allow water to seep into the crawlspace. This is due to the difference in water level between the inside and outside of the wall during flood conditions and the permeability of the soil. The dry floodproofing calculations are shown in Figure VII-6.3. 190 _ \LJFIRE Figure V11-6.1: Location Plan Ennineerina PrinciDlesand Practices of Retrofitting Flood-Prone Residential Structures VII -79 January 1995 L Chapter VII: Case Studies 311ItNQ1.. 100 YR. FUTURE WSEL. 196.4 EXIST. GRADE Figure VII-6.2: Preexisting Foundation Wall Section Detai I VII -80 Engineering Principles and Practices of R(etrofitting Flood-Prone Residential Structures January 1995 Case #6: Wet Floodproofing IOYM1T-ko0 O r10 ;n CD L4' ZS.O t~ § S i n e . 4-' p l e A d t n + k u t i W t 1 4+ b\oa C?*;on Th ib t r'< . "'V> % I rwsw#Ottcs -NCMA Nsernn4 CoocVab. rlsv-er DeiesiaKT4LaS I p. Zfl 2%4 Scc 1 e cr5c eioCS' Figure VII-6.3: Dry Floodproofing Calculations (continued) Wet Floodproofing Option This option allows the water to enter the crawlspace through vents or the access doors. This results in a reduction in the mortar joint stress to below the allowable limit. It is imperative that the openings are free of debris to sufficiently allow the water to flow through. When the water reaches its peak elevation, the wood floor framing will be partially submerged and will cause an upward buoyant force on the first floor. A conser vative approach was taken in the structural calculations, which checked the buoyant force with the entire floor joists submerged. The analysis showed that the dead load of the first floor alone is sufficient to resist the upward force caused by the water. The main floor beam and possibly the floor joists will be inundated by the water for a period of two to three hours, and structural damage could occur to the floor joists, beam, and possibly to the subflooring. Therefore, waterproofing should be applied to the floor joists to allow the implementation of the wet floodproofing option. The wet floodproofing calculations are shown in Figure VII-6.4. V1I -82 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #6: Wet Floodproofing \j'4c+I. - Fior. PvO&,iw! 0?*i -kvrrir +kyaoun Yant I Slubw p~Nme"+ .1/. (Xx .4) (-15)1 (f_. _ _ _ _._ ... "... _." Figures VII-6.7: Access Door Detail VII -88 Engineering Principles and Practices of Re&trofittingFlood-Prone Residential Structures January 1995 Case #7: Dry Floodproofing GALV. CABL ,1 ~~~CONT. L~~~~~~~~~~~~~~~~ ANCHORING SYSTEM " MANUFACTURED.BY _ fARROW; -CHANCE OR APPROVED EQUAL I | 0 SPACING OF ANCHOR ASSEMBLY SHALL 9 LONGtv ANCHOR$ AI.~ _____ 0 ~NOTEXCEED S o/e 1F orY L1 9/ Li; :)-0 'I Figure V11-6.8: Anchorage Detail for Sheds Sheds are anchored so they do not become floating debris. VII Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vll --89 January 1995 ChapterVII: Case Studies DRY FLOODPROOFING This section presents two case studies that identify procedures, methodology, and design parameters used to dry floodproof houses. Case Study #7 illustrates dry floodproofing of a house with a walkout basement in Prince George's County, Maryland. Case Study #8 illustrates dry floodproofing using a veneer wall in the Tug Fork Valley, West Virginia. CASE STUDY #7 Dry Floodproofing a House with a Walk-out Basement Henson Creek, Prince George's County, Maryland The site is a two-story wood-frame house with a walk-out basement. The first floor elevation is 211.7 and the basement floor elevation is 204.0. The top of the existing retaining wall that encompassed the walkout is 207.0 (see Figure VII-7.3). The 100-year water- surface elevation (WSEL) is 206.0 based on future upstream land use conditions (see Figure VII-7. 1). A flood protection elevation of 207.0 was utilized in this design. The foundation consists of a full basement with a walkout on the Henson Creek side of the house. The existing grade varies in elevation along the foundation wall where the highest elevation occurs in the front and slopes down toward the walkout (see Figure VII7.4). Engineering Analysis Summary The foundation walls were checked for structural adequacy against the lateral pressures exerted by the soil and the floodwater (see Figure VII-7.2). The worst case, which occurs along the front, was investigated in the structural calculations similar to Case #6. The existing walls prove to be structurally sound and able to resist the lateral forces imparted by the 1 00-year flood. Since the house has a walk-out basement with a finished floor 2.0 feet below the 100-year WSEL, the proposed replacement floodwall that wraps around the back of the house will have to retain the floodwater in addition to the soil. The present condition of the existing wall is questionable due to the numerous cracks in the joints and the cracks around the grouted pockets at the wood columns and unknown wall foundation conditions. Furthermore, the wall was not designed to resist the relatively high lateral forces occurring during the flood. Therefore, it was recommended that the wall be replaced with a reinforced concrete floodwall. Temporary supports will be required for the first-floor over- VII -90 Enaineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #7: Dry Floodproofing hang during the construction of the wall. The wood columns supporting the overhanging room should bear on top of the wall with a bearing plate to distribute the column load. A step-up/step-down entrance over the wall is required for ingress and egress to the basement. Figure VII-7. 1: Location Plan Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -91 January 1995 Chapter VII: Case Studies The following recommendations were developed based upon the engineering analysis: * Construct a new reinforced concrete wall to replace the existing wall. Top of wall must be at elevation 207.0 or higher. * Apply waterproofing to the inside basement wall to prevent leakage into the living areas of the basement. Engineering Calculations and Cost Data The cost to dry floodproof the house was estimated in 1988 dollars at $4,800. The following calculations (see Figure VII-7.2) were applied to the existing foundation to determine if the house could be retrofitted using dry floodproofing techniques. Demolish existing wall $ 500 Waterproofing $ 400 Rebuild wall $3,900 TOTAL $4,800 :II : 0 VII -92 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #7: Dry Floodproofing Figure VII-7.2: Dry Floodproofing Calculations Engineering Principles and Practices of Retrofitting Flood-Prorie Residential Structures VII -93 January 1995 Chapter VII: Case Studies F;i^ -A Vw (4.-i' z 44.~ s4. in(+15 ) (4-/ Im 7 lb > RAm-79Jb co /7.0 .: a 1loawin6 rO mm+ 1uovt^*io-i5s\ItI:n1X1 Ge4.rtr4C m",4 (4s")(4. ) z.8 + L f4z'I F 3Of 16' f t a 5Is IXlz 71,j z?.4 4 A i5Qj;5 IzS ,OpOc *I = Tj-em.4.tlu^ 4 OL 01.,.~1 AW14. * S4,a ;%4. :iHi -h tc~~~~u .:WKAW e a.a 11 Oo . FF %AL). -£,~cirTg'J'; ~ ~ d'ti~iI4 vLO -N Figure VII-7.5: Concrete Patio, Replacement Floodwall, and New Access for Basement Detail Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures VII -97 January 1995 Chapter VII: Case Studies I Figure VIl-7.6: Step and Wall Detail Elevations S VII -98 Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures January 1995 Case #7: Dry Floodproofing 41: . . z,i , i i I _ ~7 ~ i~ ~. Set. MAW' 46f t li Folz ^ ~~~~~~I. ' r¢*%> 4P1 4144~iO4 fAw x ot rI p 114~~~~~~~~_ _ _ _ _ _ _ _. l ^ 8 4XC~~~g 2 4 lZ~tg> Figure VII-7.7: Concrete Floodwall Detail VII-7.8: Downspout Connection to Drain Detail Engineering Principles and Practices of Retrofitting Flood-Prone Residential Structures Vil -99 :January 1995 Chapter VII: Case Studies . r' HIG DENSITY CAULAINOMOTH0WE$S FU KEIGHTOF WALL S3UBMI SAMPLE To COUKTy. *1/2' MT. MANSION MATERIAL FULL KEIGHT OF WAL.L I i. 11 J

, to make the installation drive active, type the drive letter desired followed by a colon (A: or B:) and press Enter. Your DOS prompt will change to A:> or B:> depending on which drive you made active. 4. Type SETUP and press Enter. This command initiates the self- installing Windows Setup program. NOTE: DOS commands are not case-sensitive and may be entered either in upper or lower case. For clarity, all DOS commands in this manual are shown in upper case. 5. Follow the instructions on the screen. The Setup program's instructions should be self-explanatory. But, if you do have questions about any of the procedures or options, you can request on-line Windows Help by pressing the F1 key. For more information, see the Microsoft Windows User's Guide. HINT: The installation routine will ask if you want to choose a "custom" installation or allow Windows to perform a "standard" installation. Most computers will operate well if you allow Windows to self-install (i.e., select the "standard," not the "custom" installation). 2-2 VERSION 1.0 12/29/94 GETTING S~TARTED I Quattro Pro for The Benefit-Cost Programs run in QUATTRO PRO FOR WINDOWS Windows (QPW) (QPW). You must have QPW (VersIon 5.0) installed on your computer before loading or running the Benefit-Cost Programs. To Install QPW: 1. Be sure you are in Windows (i.e., install Windows first): open Windows if it does not automatically come up when you turn on your computer. At the DOS prompt, C:\>, to open Windows, type WIN If this command opens Windows, proceed to Step 2. If not, then an error message, "bad command or file name," will appear. If this error message appears, it means that Windows is not in the path list and you must change directories before opening Windows. At the DOS prompt, C:\>, to change directories, type CDWINDOWS This command changes the DOS prompt to C:\WINDOWS>. At the DOS prompt, C:1WINDOWS>, to open Windows, type WIN 2. Insert the QPW Disk I in the drive (A: or B:) you want to use for the installation and close the drive door. 3. With your mouse, point the cursor on Elie on the menu bar (at the top of your screen), press and hold the left button of your mouse. While holding down the left mouse button, move the mouse until Run... is highlighted and release the mouse button. Or, Click on Eile, then click on Run... 2-3 VERSION 1.0 12/29194 GETTING STARTED 4. On the Command Line (i.e., inside the box which will appear next on your screen, as shown below), type -A:INSTALL.EXE or B:INSTALL.EXE depending on which drive the QPW disk is in. Be sure to type the command exactly as written: do not add spaces or change punctuation. Then left-clickthe mouse on OK. 3 : 5. Enter the requested information in the Installation Dialog Box which will appear on your screen. Accept the default choice of QPW for the Quattro Pro directory. 6. Quattro Pro will ask you for various information during the installation. Simply type the response and press Enter or click the mouse on OK. The default (standard) settings are usually suitable for your first installation of Quattro Pro. 7. After entering the information requested in the Installation Dialog Box (e.g., your name), click on Install to continue. 8. Follow instructions (e.g., change from Disk I to Disk 2 to Disk 3 etc.) as they appear. 9. After you have completed these steps, your QPW installation will be complete! I 2-4 VERSION 1.0 12/29/94 GETTING START-ED installing the Benefit-Cost Programs Network Computer networks may be set up and managed in many different Systems ways. Therefore, this manual cannot give detailed instructions for installing the Benefit-Cost Programs on a specific network system. To install the programs on a computer which is connected to a network system, give the program disks and the User's Manual to your computer system operator or network administrator. After installation is completed, go to the Start QPW section on page 3-1. Stand-Alone 1. Turn on your computer. Computers: I 2. If you are not at a DOS prompt (such as C:\>) either exit from Windows to DOS, or select a DOS prompt from within Windows. To exit from Windows, click on Eile on the menu, then click on Exit. The program will display: "This will end your Windows Session." Click on OK. Your screen will show: C:\> If your hard disk drive is designated D, or some other letter, that letter will appear in place of C; 3. To install either the Riverine or Coastal A-Zone programs, insert the first Benefit-Cost Program disk (3.5") in either the A or B drive of your computer (whichever floppy drive is the high density 3.5" drive); 4. At a DOS prompt (C:\>), If the Program diskette is in the A drive, type: A:INSTALL A: C: If the Program diskette is in the B drive, type: B:INSTALL B: C: The install routine will automatically ask for the second Program disk at the proper time. 5. The install routine will automatically create a new subdirectory on your C drive: C:%BCFLOOD or C:ABCCSTA for the Riverine and Coastal programs, respectively. 2-5 VERSION 1.0 12/29/94 GETTING :STARTED VERSION i .0 12/29/94 GETTINGSTARTED 6. Two files will be loaded into the C:XBCFLOOD or C:IBCCSTA directory: A. An example file with all data entries filled in: BCEXAMP.WBI B. A blank file, for user data input: BCBLANK.WBI 7. PROGRAM INSTALLATION IS COMPLETE! is 2-6 VERSION 1.0 12/29/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS Start Windows Start QPW CHAPTER 3 PROGRAM BASICS This chapter provides basic information about starting and running Quattro Pro for Windows and the Benefit-Cost Programs, along with helpful hints. Starting Quattro Pro For Windows (QPW) Quattro Pro For Windows (QPW) is a Windows program; therefore you must first start Windows before starting Quattro Pro. If you are not already in Windows, type WIN at a DOS prompt (e.g., C:\>) to start Windows. See page 2-3 for more information. After starting Windows, click the left mouse button on the symbol (the "icon") or the group window labeled Quattro Pro for Windows (QPW). Then, double-click the left mouse button on the QPW icon within the window. Quattro Pro for Windows works very much like any other Windows spreadsheet (e.g., Lotus 1-2-3 or Excel) or.any other Windows program, including word processors (e.g., WordPerfect or Microsoft Word). Quattro Pro commands are initiated by clicking on pull-down menus at the top of the screen or by clicking on the speed buttons below the menu lines. To use the Benefit-Cost Programs, you need to know only a little about Quattro Pro. Once a Benefit-Cost Program is loaded, the data entry, calculations, and printing of results can be accomplished entirely within the program, with minimal use of Quattro Pro commands. 3-1 VERSION 1.0 12/29/94 PROGRAM BASICS Opening Files The menu bar along the upper edge of the QPW window will display a Eile command at the left side. Click on the File command. When the menu opens, click on the Open... line. The screen will display the Open File Dialog Box which contains two boxes side by side: File Name and Directories. If the C: drive is not listed at the top of the Directories list, double click on the C: in the Drives box on the bottom center of the screen. Use the mouse to move the cursor to the BC_ FLOOD or BCCST_A directory where the Benefit-Cost Programs are located, and double click. All of the files ending in .WB1 will be listed in the File Name box at the left. Double click on the BCEXAMP.WBI line to load a completed example, or on BCBLANK.WBI to load a blank spreadsheet. Or, files may be opened by clicking once on the file name and then on OK. 3-2 VERSION 1.0 12/29/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS The computer will load a Benefit-Cost Program. Loading may take from a few seconds up to several minutes, depending on the computer. The bottom right corner of the screen (Status line) will display WAIT while the model is loading and READY when the model is loaded. Do not attempt to enter any commands while WAIT is displayed! As you continue to use the Benefit-Cost Programs and save files, the File Name box will contain the names of all of your files which have the .WB1 ending. Double-clicking on the desired file will open any of these files. Please see Naming and Saving Files on page 3-7. I Screen Display I When a Benefit-Cost Program is loaded, the first screen visible is the Sign-On Screen which identifies the program title, version, and date. Zoom List If the words extend past the right-hand side of your computer screen or if the image is too small, change the Zoom List by following these steps: 1. Click on the Zoom List arrow, located in the second row of symbols (the productivity tools 100 SpeedBar) at the top of the screen; 2. While holding down the left-hand mouse button, move the mouse until the correct value (e.g., 80) is highlighted. It may take a little trial-and-error to determine the best value for your screen. Changing the Zoom List setting changes the size of the screen display. I 3-3 VERSION 1.0 12/29/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS Moving Around in the Programs W Several Easy There are several easy ways to move around in a Benefit-Cost Ways Program: 1. Use the mouse to place the cursor wherever you want to be on a page and click on that location. 2. To move left-right on a page, use the cursor arrows on the keyboard, or the horizontal scroll bar at the bottom right of the screen. 3. To move up-down on a page, use the cursor arrows on the keyboard? or the vertical scroll bar at the right hand edge of the screen. 4. To move to the top of any page in a program, press the Home button on the keyboard. 5. To proceed sequentially through a Benefit-Cost Program, click on the Next Screen Button, at the bottom of each page. 6. To move to a specific location within a program, use the custom Menu Tree (described next) which appears at the top of the screen. Click on the desired menu item; the submenu (a list of available choices) appears. Click on the desired submenu item. Benefit-Cost The Benefit-Cost Programs are driven from a customized menu tree. Menu Tree The menu appears at the top of the display screen (after the model is loaded): tIlei E'odeI aarRis~le .i..evelOne ,e/Dat\Lees~trst~ Menu items can be accessed by clicking on the desired menu label or by the IX keyboard command, where "X"indicates the underscored letter in the menu name. For example, Results can be accessed by clicking on Results or by typing IR. In addition to the main menu, there are submenus which appear when a main menu heading is clicked on. Submenus are accessed in the same manner as the main menu headings. S 3-4 VERSION 1.0 12/29/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS For example, to move to the Depth-Damage Function screen, click on Level Two Data,then Click on luilding Depth-Damage Function. 7 : S * . I __ Mtg~to~rj~ Ef E z .e X The complete Benefit-Cost Menu Tree is given below. CUSTOMIZED BENEFIT-COST MENU TREE File Save Save As... Quit Model Version Color Codes Level One Data Project Information Bluilding Data Building Contents Displacement Costs Value of Public/Nonprofit Services Bent & Business Income Mitigation Project Data Elood Hazard Risk Level Iwo Data fluilding Depth-Damage Function Contents Depth-Damage Function Displacement Time Eunctional Downtime Mitigation Project Effectiveness Results Damages Before Mitigation Damages After Mitigation Benefits Benefit Cost Results Summary I 3-5 VERSION 1.0 12/29/94 PROGRAM BASICS 10 12/29194 VERSION PROGRAM BASICS I Print i summary Report Graph HazardData Graph Damages Before Mitigation Graph Damages After Mitigation Graph Benefit-Cost Results All Graphs 3-6 VERSION I.0 12/9/9Q14 PROGRAM BASICS VER.IflN 1fl 12129/94 PROGRAM BASICS Basic Commands and Procedures Naming and Each benefit-cost analysis file you wish to save MUST have a unique Saving Files name to avoid writing over the original file. If you choose (i.e., click on) the Save command, the model will automatically name your file NEWBC.WB1. I Save However, if you choose the Save command subsequently to save a different file, you will be asked if you wish to replace (write over) the existing file. If you choose Replace your NEWBC.WB1 file will be replaced. Save As... If you choose Save As... a unique name can be entered as a file is saved. Click on Eile (in the menu on the top line of the screen), then click on Save As... Muidel 3-7 VERSION 11.0~12/29/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS The screen will display the Save BC File As Dialog Box. Click on the Eile Name box, then type in the new name, e.g., RUNI7.WB1, as shown below. Use the Backspace or Delete keys to edit any name which automatically appears in the box. After entering the desired new file name, click on OK and the file will be saved with its new name. Names can have up to eight letters or numbers, then a period, followed by three letters or numbers, e.g., RUN12345.WBI 3-8 VERSION 1.0 12129/94 PROGRAM BASICS VERSION 1.0 12/29/94 PROGRAM BASICS l OOPSI If you accidentally overwrite one of the original Benefit-Cost Program If you overwrite files by saving a file with user-entered data without changing the name, the programfile the original program file will be lost (overwritten by the new file). To recreate the original program file, check to see if a backup copy exists: it will have the same name as the original, followed by a .bak extension (ending), e.g., BC_EXAMP.BAK or BCBLANK.BAK. Rename this file with the original name. 1. Click on the File menu at the top of the screen. 2. X Click on Open, to open the Open File Dialog Box. 3. Type *.bak in the File Name box to see if any back-up files exist. 4. Next, Qpen the .bak file (see page 3-2 for instructions on opening a file). 5. Select Save As and save the file with the desired name, as describedon page3-7, Naming and Saving Files. Helpful Hint: If all else fails, reinstall the file from the original floppy disk as described on page 2-5, Installing the Benefit-Cost Programs. Start a New If you want to do another benefit-cost analysis (i.e., run the same Benefit-Cost Benefit-Cost Program again, with different inputs): Analysis 1. Save the existing open file with a new name (see Naming and Saving Files, page 3-7). 2. Click on Eile (in the menu at the top of the screen), hold down the left mouse button until Quit is highlighted. 0~~~~~~~ 3. Click on Eile, then click on _Qpen to start a new analysis (see Opening Files, page 3-2). Exit From a 1. Save your work with a new name, by using the Benefit-Cost FilelSave As command described above. Program 2. Click on Eile, then click on Quit to leave the Benefit-Cost Program. I 3-9 VERSION 1.0 12/29/94 PROGRAM BASICS Run a Different Benefit-Cost Program Exit from QPW If you want to run a different Benefit-Cost Program (e.g., the Coastal A-Zone Program instead of the Riverine Program): 1. See Opening Files on page 3-2. 2. Select the appropriate directory (e.g., BCFLOOD or BCCSTA) for the desired Benefit-Cost Program. 3. Open BCEXAMP.WBI or BCBLANK.WBI or another previously named file. To exit from QPW, you must first exit from the Benefit-Cost Program. With the mouse, highlight Elie and Quit. This closes the program without saving it (so save the file first, if desired, as described above). Next, with the mouse, highlight Elue, then Exit to close QPW and return to the Windows screen. Exit from To leave Windows, click on Elue, then on Exit. The screen will display Windows a dialog box with "This will end your Windows Session.t' Click on OK to return to a DOS prompt. 3-10 VERSION 1.0 12/29/94 PROGRAM BASICS Cell Colors Unprotected Blocks Protected Blocks Before you begin the data entry process, note that all areas (blocks or "cells") of the program screens are color coded to remind the user what type of information each cell contains. The cell type appears in the Style List window when the cursor is clicked on a cell. The Style List window is in the upper SpeedBar. liformation 112 In the Benefit-Cost Programs, background space is white and identifying labels (which cannot be changed) have black text on white backgrounds. There are seven colors which indicate different types of data entries or calculated results: User data entries can be made ONLY in PINK, GREEN, BLUE, or RED blocks. "Unprotected" means that data entries CAN be made within these blocks. Blocks colored ORANGE, YELLOW, and PURPLE are protected. The background, or normal blocks, which appear WHITE are also protected. User entries CANNOT be made in these blocks. To change information in PURPLE blocks (Carry Over) the original data entries in the PINK or GREEN blocks must be changed. To change entries in the ORANGE or YELLOW blocks, the underlying selections or data entries which affect these blocks must be changed. 3-11 VERSION 1.0 12/29/94 PROGRAM BASICS Data Entry Correcting Errors To enter data into a block (cell) in the program, first move the cursor to the block where you want to enter the data. Then, type the desired information. As you type, the characters appear in the Input Line below the menus and speed buttons. i Cross Headquarters I Only when you press Enter or an arrow key or click the check mark button (/) does Quattro Pro move the characters into the block (cell). Thus, you must press Enter or an arrow key or click the check mark button (V) to actually make the data entry which you have typed. If you attempt to enter data in cells which are not GREEN, PINK, BLUE, or RED you will see a "protected cell' error message. Other cells are "protected" to prevent inadvertent changes to the program. As with other error messages, click on OK or press the Esc key to return to data entry. If you make a mistake while typing, press the Backspace key on the keyboard to erase. To clear the entire entry, click the X box or press the Esc button on the keyboard. 3-12 VERSION 1.0 12/29/94 PROGRAM BASICS Entering Commas and Dollars Entering Addresses Syntax Error After pressing Enter, if you find you made a typing mistake or want to change an entry, first select the cell which you wish to change by clicking on the cell. Then, type the entry over again or click inside the text on the Input Line (see Data Entry above) and edit it there. To delete an entry without replacing it, just select the cell (by clicking on the mouse in the desired cell) and press the Del button on the keyboard. Another option is to use the Delete button to delete the entry. Click on the cell with the mistake, then move the mouse to the Delete button (on the left side of the bottom Tool Bar) and click. To Undo any entry or change, move the cursor to the cell and left click the mouse, then highlight and click on the Undo (pencil eraser) icon (on the bottom right of the Too l Bar). QPW can't accept number entries which include a dollar sign "$" or commas ",". Thus, twenty thousand square feet must be entered as 20000 and a cost of $10,000 must be entered as 10000. The "$" and "," are inserted automatically. If you forget and include a "$" or a "," the model will respond with a "Syntax error" message. Click on the OK, or press the Esc keyboard button, then enter correctly the information requested. When entering the address (or any combination of letters and numbers which beggin with a number), first type an apostrophe (') followed by the number and street name. The'tells Quattro Pro that the entry is text, not numbers. If you forget to include the apostrophe, a "Syntax error" message will appear. Click on the OK, or press the Esc keyboard button, then enter correctly the information requested. 3-13 VERSION 1.0 12/29/94 TUTORIAL CHAPTER 4 TUTORIAL II This chapter reviews the process of loading Quattro Pro for Windows and a Benefit-Cost Program, and works through a sample LEVEL ONE (see definition below) data entry exercise and benefit-cost analysis. This tutorial is provided primarily for the less experienced computer user. To examine an example of a complete benefit-cost analysis, open the BCQEXAMP.WBI file in either the BCFLOOD or the BCCST_A directory. These BC EXAMP.WB1 files have all of the data entries already completed. To use the tutorial to enter data in a blank benefit- cost model, follow the instructions which start on page 4-3. LEVEL ONE and LEVEL TWO Benefit-Cost Analyses A LEVEL ONE (Minimum Data) Benefit-Cost Analysis, relies heavily on default values and requires the minimum of user-specified data entries. A LEVEL TWO (Detailed) Benefit-Cost Analysis, relies less on default values and incorporates much more building-specific data. LEVEL ONE (Minimum Data) B-C Analysis By entering the information on the LEVEL ONE Data pages and the Flood Hazard Data, the program will perform a Benefit-Cost analysis of the proposed mitigation project. Additional numerical values which the model requires for its calculations are already included in the program as "default values." For general guidance on how to perform a benefit-cost analysis, see Chapter 5, Benefit-Cost Programs: Guidance. For a detailed explanation of the data entries for a LEVEL ONE analysis, see Chapter 6, Benefit-Cost Programs: Level One Analysis. For a detailed explanation of flood data entries, see Chapter 7, Benefit-Cost Programs: Flood Hazard Risk. 4-1 VERSION 1.0 12/29/94 TUTORIAL VERSION 1.0 12/29/94 TUTORIAL LEVEL TWO (Detailed) B-C Analysis Users are encouraged to perform a LEVEL TWO (Detailed) analysis whenever possible. LEVEL TWO analyses will provide the most accurate results by incorporating much more building-specific data and judgments than a LEVEL ONE analysis. See Chapter 8, Benefit-Cost Programs: Level Two Analysis for a detailed discussion of Level Two data entry. The following tutorial is for the LEVEL ONE (Minimum Data) Benefit- Cost Analysis. 4-2 VERSION 1.0 12/29/94 TUTORIAL Step One Step Two Step Three Step Four VERSION12/29/94 TU TORIA 1.0 Starting the Tutorial Start Quattro Pro for Windows (QPW). See page 3-1. Open the desired Benefit-Cost Program file. See instructions (Opening Files) on page 3-2. For the tutorial, open the BC BLANK.WBI file in the BCFLOOD directory. The Sign-On screen appears after a Benefit-Cost Program is loaded. Adjust the Zoom List factor which controls the size of the screen display, if necessary. See instructions on page 3-3. Proceed through the Data Input process, as outlined below in the tutorial example. This example leads you through the LEVEL ONE (Minimum Data) benefit-cost analysis data input process. Click on the NEXT SCREEN button at the bottom of the Sign-On Screen to begin the data entry process. Clicking this button on the Sign-On screen moves you to the LEVEL ONE DATA screen, where the data entry process begins. 4-3 VERSION 1.0 12/29/94 TUTORIAL VERSION TUTORIAL 1.0 12129/94 Building Name Address OOPSI Help City, State, Zip Code PINK Blocks (Information Only). With your mouse, move the cursor to the first pink-colored block, Building Name, and click on the cell. IMPORTANT:the cursor must be in the first space inside the pink box, not to the left of it. Type the name of the building, i.e., City Office Annex. Press the Enter key. As you make data entries, remember that PINK blocks are for information only;they serve to identify the project under evaluation, but do not affect numerical benefit-cost results. Entries in the RED block and the GREEN blocks do affect numerical results. Then, with the mouse or the arrow keys, move the cursor to the street Address and enter it in the followingway: '55 A Street If you forget to start your entry with an apostrophe (') an error message will be displayed. The address (and all combinations of numbers and letters which begin with a number) MUST be entered with a single apostrophe (') preceding the address, e.g., '55 A Street. Ifnot entered this way, a "Syntax error" message willappear: click on the OK of the error message and add the apostrophe (see page 3-13). Then, press Enter. Move to the next entry. PINKBlock (Information Only). Enter the city, state and zip code for the building: Cape Squirrel, VA 22222. Move to the next entry. 4-4 VERSION 1.0 12/29/94 TUTORIAL VERSION 1.0 12/29194 TUTORIAL Owner PINK Block (Information Only). Enter the name of the building's owner. This may be an agency, a private party,4etc. Enter: City of Cape Squirrel. Move to the next entry. Contact Person : 'PINK1Block (Information Only). Enter Sam Smith, City Manager, for the building's manager, or other contact person who could provide information about the building to the analyst. Move to the next entry. Disaster Number PINK Block (Information Only). Enter disaster number FEMA-000- IDR-VA. Move to the next entry. Project Number PINK Block (Information Only). Enter project number 123456. Move to the next entry. Application Date PINK Block (Information Only). Enter January 1, 1994. Move to the next entry. Discount Rate RED Block (OMB Policy). The discount rate of 7% is already entered. Move to the next entry. Scenario Run ID PINK Block (Information Only). Enter the scenario run number 1. Move to the next entry. Analyst PINK Block (Information Only). Enter your name. Move to the next entry. 4-5 VERSION I1.0 12/29/94 TUTORIAL VERSION 1.0 12/29/94 TUTORIAL BUILDING TYPE BUILDING INFORMATION Zero Flood Depth Elevation Numberof Stories Construction Date Historic Building Controls 3 flAA~~~~~~~~ You must use the mouse to click on the appropriate button; the arrow keys will not operate these buttons. For this example, click on the button labeled: 2 story w/o basement. This choice will automatically appear in the purple cell labeled "Building Type Selected." GREENBlock (Data Input). Enter 6 as the Zero Flood Depth Elevation (top of the lowest finished floor) for this building. Move to the next entry. PINK Block (Information Only). Go to the Number of Stories Above Grade box and enter 2. Move to the next entry. PINK Block (Information Only). Go to the Construction Date box and enter 1965. Move to the next entry. PINKBlock (Information Only). Go to the Historic Building Controls box and enter No. Move to the next entry. 4-6 VERSION 1.0 12/29/94 TUTORIAL BUILDING SIZE AND USE Total Floor Area (Sf) Syntax Error Area Occupied by Owner or Public/Nonprofit Agencies BUILDING VALUE Building Replacement Value ($/sf) GREEN Block (Data Input). Enter 2000 (two thousand) without a comma. The screen will display this as 2,000 when you confirm the entry by pressing Enter or move to the next data entry block. If you make a mistake, use the backspace key to erase, then enter the information correctly. If you made a mistake and have already pressed the Enter key, you will see an Error Message. Follow the instructions below. Spreadsheets such as Quattro Pro can't accept numbers which include a dollar 'sign ($)or commas. Thus, twenty thousand must be entered 20000 and a cost of $1 0,000 should be entered as 1 0000: the I$" and the "," are entered automatically. If you forget and include a "$" or a "," the program will respond with a "syntax error" message. Click on the OK, then enter correctly the information requested. GREEN Block (Data Input). Enter 1500 for the total amount of space (in square feet) occupied by the owner or public/nonprofit agencies. Move to the next entry. Relacement Buldn Vatlue($ -. :T.otal BuildingReplacementVaill BuildingDamage that would Ren Re GREEN Block (Data Input). Enter 75 as the building's value per square foot. Move to the next entry. 4-7 VERSION 1.0 12/29/94 TUTORIAL VERSION 1.0 12/29194 TUTORIAL Total Building Replacement Value Building Damage that would Result in Demolition Contents Description Total Value of Contents Value of Contents ($Isf) YELLOW Block (Result). The program automatically calculates $150,000 as the building's total replacement value and displays it in the yellow block. Move to the next entry. DemolitionPercent GREEN Block (Data Input). Enter 50 (fifty) for the percent of building damage at which demolition and replacement (rather than repair) would be expected to occur; this value is also known as the "demolition threshold." Move to the next entry. Demolition Value YELLOW Block (Result). The programdisplays$75,000 for the dollars of building damage at which demolition and replacement (rather than repair) would be expected to occur. Move to the next entry. 1:-Ul M00Ej k v_ PINK Block (Information Only). Enter office furniture, computers & files as the description of the building's contents. Move to the next entry. GREEN Block (Data Input). Enter 60000 as the total contents value. The "$" sign and the comma are entered automatically. Move to the next entry. YELLOW Block (Result). The program displays $25.00 as the value of contents in dollars per square foot of building space. Move to the next entry. 4-8 VERSION 1.0 12/29/94 TUTORIAL : A 0 3 0 SOUAIA Rental Cost of Temporary BuildingSpace ($/sflmonth) Rental Cost of Temporary Building Space ($/month) Other Costs of Displacement ($/month) Total Displacement Costs ($Imonth) GREEN Blocks (Data Input). Enter 1.50 (one decimal point five zero) as the rental cost of temporary building space in dollars per square foot per month. Move to the next entry. YELLOW Block (Result). The program displays $2,250 as the monthly rental cost of temporary building space. Move to the next entry. GREEN Block (Data Input). Enter 500 (five hundred) as the estimated cost of all other non-rent costs associated with this displacement. Other costs include moving costs, temporary equipment, temporary furnishings, etc. Move to the next entry. YELLOW Block (Result). The program will display $2,750 as the calculated total displacement cost per month. Move to the next entry. 4-9 VERSION 1.0 12/29/94 TUTORIAL VERSION 1.0 12/29/94 TUTORIAL s _A*lS Description of Services Provided Annual Budget of Public/Nonprofit Agencies Is Rent Included in this Budget? User-Entered Rent Estimate ($/month) Cost of Providing Services ($/day) PINK Block (Information Only). Enter City Planning Office. Move to the next entry. GREEN Block (Data Input). Enter 195000 (one hundred ninety five thousand) as the annual budget for allthe public/nonprofitagencies operating out of this building. This is the total annual operating budget 0 for public or nonprofit agencies in this building. The total budget should exclude pass-through amounts such as Social Security payments. Move to the next entry. Click on the YES button to indicate that rent is included. The program displays "Rent Included" under the $195,000 annual budget cell just above. When rent is not included in the annual budget, the program calculates a default or proxy rent based on the value of the building and displays it in the YELLOW Block (Result) on the next line. Move to the next entry. GREEN Block (Data Input). Leave this entry blank, because rent is already included in the budget estimate. Move to the next entry. YELLOWBlock (Result). The programcalculates $534 as the estimated daily cost of providing services from this building. Move to the next entry. I 4-10 VERSION 1.0 12/29/94 TUTORIAL Post-Disaster Continuity Premium ($/day) Total Value of Lost Services ($/day) Monthly Rent from Tenants Net Income of Commercial Businesses GREEN Block (Data Input). Enter 500 for a $500 per day continuity premium. Move to the next entry. YELLOW Blocks (Results). The program displays $1034 as the total value of lost services per day. Move to the next entry. __ I GREEN Block (Data Input). Enter 600 (five hundred), as the total monthly rent received from all tenants in the building, excluding public/nonprofit agencies ($/month). Move to the next entry. GREEN Block (Data Input). Enter 1500 (one thousand five hundred) as the estimated net income of commercial businesses in the building ($/month). Move to the next entry. 4-11 VERSION 1.0 1 2/29/94 TUTORIAL VERSION12/29/94 TUTORIAL 1.0 A A_ * 3k ** Select Mitigation Measure Project Description Project Useful Life Mitigation Effectiveness Estimates F eCt ?=IF Ea With the mouse, click on the Elevation button. The program will display this choice in the purple cell. PINK Block (Information). Enter Elevate 5 feet. Move to the next entry. GREENBlock (Data Input): Enter 30 as the years of useful life expected from this mitigation measure. Move to the next entry. EtrEfc~eesEtmtsfrteMtgto esr IOSta'froEfftitDettive at Deh Enter 4 in the Elevation row under the 100% Effective to Depth column header (see Chapter 6, Benefit-Cost Programs: Level One Analysis for a discussion of mitigation project effectiveness). The program displays NIA(not applicable) in the 0% Effective at Depth column for the Elevation row because this is calculated automatically from the building depth-damage function. NIAalso appears in the Relocation/Buyout rowbecause such measures are assumed to be 100% effective at all depths. Although values may appear in other rows (from previous uses of the program), the program only "reads" (uses) the values in the row which corresponds to the mitigation measure type selected. Move to the next entry. 4-12 VERSION 1.0 12/29/94 TUTORIAL MITIGATION COSTS Mitigation Project Cost Base Year of Costs ANNUAL MAINTENANCE COSTS ($NYEAR) Present Value of Annual Maintenance Costs RELOCATION COSTS FOR MITIGATION PROJECT Relocation Time Due to Project Rental Cost During Occupant Relocation GREEN Block (Data Input). Enter 40000 (forty thousand) as the mitigation project cost, excluding relocation costs. Move to the next entry. PINK BLOCK (Information Only). Enter 1994. Move to the next entry. GREEN Block (Data Input). Enter 500 (five hundred) as the annual maintenance costs. Move to the next entry. YELLOW Block (Result). The program calculates $6,205 as the present value of annual maintenance costs. This calculation is based on the annual maintenance costs, the project useful lifetime, and the discount rate. Move to the next entry. In this section, the time and costs associated with occupant relocation during the construction of the mitigation project are estimated. GREEN BLOCK (Data Input): Enter 2, for two months of relocation time necessary for the mitigation project. Move to the next entry. GREEN Block (Data Input): Enter 2.00 for $2.00 per square foot per month as the rental cost during occupant relocation for the mitigation project. Move to the next entry. YELLOW Block (Results): The program displays $3,000, as the monthly rental cost incurred during occupant relocation for the mitigation project. Move to the next entry. 4-13 VERSION 1.0 12129f94 .TUTORIAL VERSION 1.0 12/29/94 TUTORIAL Other Relocation GREEN Block (Data Input). Enter 500 (five hundred) dollars in other Costs ($/month) relocation costs per month. Move to the next entry. Total Relocation YELLOW Block (Result). The program displays $7,000 as the total Costs relocation costs for the mitigation project. Move to the next entry. TOTAL YELLOW Block (Result): The program displays $53,205 as the total MITIGATION mitigation project costs. This total includes the mitigation project costs, PROJECT the present value of the annual maintenance costs, and the relocation COSTS costs for the project. Move to the next entry. A A, Flood Data GREEN Blocks (Data Input). Complete the Flood Data chart with the data as shown above, for Flood Frequency, Discharge and Elevation. These data, along with the Zero Flood Depth elevation of the facility under evaluation determine the extent of flood risk at the site. For more information about how flood hazards are modeled in the program, see Chapter 7, Benefit-Cost Programs: Flood Hazard Risk. To view the calculated flood estimates, move down on the flood hazard page with the arrow keys or mouse. The flood estimates are updated automatically whenever you move to any page, other than the Flood Hazard page. NOTE: This tutorial is for a Riverine flood example. The Coastal A- Zone flood data entry is slightly different. See Chapter 7, Benefit-Cost Programs: Flood Hazard Risk. 4-14 VERSION 1.0 12/29/94 .TUTORIAL *-ilW::@u S-E~uP mfI0 Use the mouse to highlight Results on the menu, and then, while holding down the left button, move the mouse until Benefit-Cost Results is highlighted. The program will then move to the Results screen. Present Value Coefficient YELLOW Block (Result). The program displays 12.41 as the present value coefficient. The Present Value Coefficient is the present value of $1.00 per year in benefits received over the project useful life time period. The Present Value Coefficient is calculated from the Project Useful Lifetime and the Discount Rate, which are carried over, PURPLE Blocks (Carry Over), from the LEVEL ONE Data entry page and displayed here for reference. Summary of Expected Damages and Benefits Expected Damages and Benefits Table YELLOW Blocks (Results). For each category listed in the table above, the program displays the calculated results: Expected Annual Damages Before and After Mitigation, Expected Annual Benefits, and the Present Value of the Annual Benefits. See Chapter 9, Benefit-Cost Programs: Results, for a detailed discussion of these results and how to interpret them. 4-15 VERSION 1.0 12129194 TUTORIAL BENEFITS AND COSTS Project Benefits Project Costs Benefits Minus Costs Benefit-Cost Ratio Next YELLOW Block (Result). The program displays $36,691 as the present value of damages avoided, which are the calculated benefits for the mitigation project. This value is the "bottom line" -the calculated benefits of the project -- corresponding to all of the data inputs made previously. YELLOW Block (Result). The program displays $53,205 as the total costs of the proposed mitigation project. YELLOW Block (Result). The program displays ($16,513) as the difference between the Project Benefits (i.e., the present value of total damages and losses avoided) and -the total Project Costs of the mitigation project. This result indicates that for the particular project evaluated the benefits are less than the costs by $16,513. YELLOW Block (Result). The program displays 0,69 as the ratio of benefits to costs for the proposed mitigation project. This means that each $0.69 in benefits from the project carries a cost of $1.00. Thus, project costs are greater than the benefits. Click on the NEXT SCREEN button and go to the next results screen, SUMMARY. The summary contains a concise compilation of all of the data inputs which affect the numerical benefit-cost results. 4-16 VERSION 1.0 12/29/94 TUTORIAL I PRINT MENU TO END THE TUTORIAL The Print Menu controls printing of the Summary page, the Report, and any or all of the graphs included in the Benefit-Cost Program. The Summary page contains a one-page compilation of all of the data inputs which affect the numerical benefit-cost results. The Report is a printout of the Data and Results screens from the Benefit-Cost Program, without the Help buttons and without the bright color shadings. Click on the Print menu label to access the printing options. The program will automatically display the range of available choices to print. Click the mouse button on the appropriate item in the Print menu to print any desired item. After completing the tutorial session, please EXIT from the tutorial Benefit-Cost Program. To save your tutorial example: First, save your work (if desired) with a new name, by using the FilelSave As command described above. To closethe tutorial file: Click on File then click on Quit. To conduct another benefit-cost analysis: Use the mouse to move the cursor to File and hold down the left button. Then highlight Qpen... Open the new file, either BCEXAMP.WB1 or BCBLANK.WB1, as described in the section, OPENING FILES on page 3-2. If you don't wantto do anotherbenefit-costanalysis: Click on File, then click on Exit to leave Quattro Pro and return to Windows. To exit from Windows, click on Eile, then on Exit. The screen will display a dialog box with "This will end your Windows session." Click on OK to return to a DOS prompt. 4-17 VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance CHAPTER 5 BENEFIT-COST PROGRAMS: GUIDANCE I I Introduction The accuracy, validity, and usefulness of any benefit-cost analysis depends on the correctness of the input data. Any benefit-cost analysis in which input data such as the building depth-damage function or the effectiveness of the mitigation measure do not realistically reflect the particulars of the building and mitigation project under evaluation cannot provide useful results. Each analyst conducting benefit-cost analysis has the responsibility to ensure that all data inputs are reasonable, defensible, and well- documented. The programs process all of the data inputs in a mathematically correct manner, but the programs cannot produce correct results when incorrect data are entered. The analyst has control over the data inputs and thus responsibility for the results. Thus, a good faith effort must be made to obtain accurate input data for benefit-cost analysis. The zero flood depth elevation of the building under evaluation is particularly important because this markedly affects the degree of flood risk to the building and thus markedly affects the benefits of avoiding future flood damages. I e nE efi th c ost a al ysi s n diusx b ~ re Hieweditoensu e hat data pu ts I jilding i ~deevlaion '-' E I 5-1 VERSION 1.0 12129/94 B-C PROGRAMS: Guidance Exact Data vs. Estimates Data Requirements Despite the importance of accurate data input for benefit-cost analysis, very few of the data inputs for benefit-cost analysis of hazard mitigation projects will be exact numbers. However, if exact numbers are available for some of the data inputs, enter them. For example, if the zero flood depth elevation,the square footage of the building and the value of contents are known, then enter the known values. In most cases, however, only a few of the required data inputs will be known exactly. Typically, most of the data inputs for benefit-cost analysis willbe estimates, rather than exact numbers. Ifexact values are not available, it is acceptable to use approximate values or your best judgement. For example, if a neighborhood has houses of approximately 1000 square feet and an average value of $60,000, then it is acceptable to use these values as the average for the neighborhood. It is not necessary to determine that one house is 927 square feet and another 1083 square feet, or that one house is worth $56,000 because the roof leaks and another is worth $62,500 because it has an elegant fireplace in the living room. For most small projects, approximate values may provide an acceptable benefit-cost analysis. As project size (i.e., cost) increases, or for projects whose benefit-cost ratio is very close to one, it may be worthwhile to devote more time and effort to obtaining better estimates or more exact values. The level of detail, amount of data required, and level of effort necessary to conduct a benefit-cost analysis of a hazard mitigation project may vary substantially depending on the scale of the project and the desired accuracy of the analysis. The benefit-cost software is flexible and is designed to accommodate different levels of analysis corresponding to different scales of projects and desired level of accuracy. The simplest analysis, requiring the least project-specific data, can be completed using "default" or reference data built into the programs, along with a minimum amount of required project-specific data. More detailed analyses can, if desired, incorporate a large body of project-specific data. 5-2 VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance LEVEL ONE A LEVEL ONE (Minimum Data) benefit-costanalysis can be (Minimum Data) conducted using "default" or reference data built into the programs. B-C Analysis See Chapter 6, Benefit-Cost Programs: Level One Analysis for more detailed information. A LEVEL ONE (Minimum Data) analysis relies heavily on default data built into the Benefit-Cost Programs. Completing a LEVEL ONE benefit-cost analysis requires entering the following information: 1. All "required" data on the LEVEL ONE Data screens, which include: a. Project Information. These data, discussed in Chapter 6, page 6-3, identify the facility, the project under evaluation, and the discount rate. Except for the discount rate, these entries do not directly affect the numerical benefit-cost results. 5-3 VERSION 1.0 12/29/94 0B-C PROGRAMS: Guidance Specification of an appropriate discount rate is discussed in Chapter 6, Benefit-Cost Programs: Level One Analysis. The discount rate is fixed by the Office of Management and Budget (OMB) and FEMA policy and is NOT a user-adjustable data variable for FEMA-funded projects. This entry should be checked for appropriateness. The appropriate rate for Section 404 or 406 Hazard mitigation projects is defined by OMB and updated annually. b. Building Data. These data, which are discussed in Chapter 6, page 6-5, contain essential information, including the zero flood depth of the building, and building replacement value. c. Building Contents. These data, which are discussed in Chapter 6, page 6-9, identify the contents and the contents value. d. Displacement Costs Due to Flood Damage. These data, which are discussed in Chapter 6, page 6-10, identify the cost of temporary building space and other costs associated with displacement from the building due to flood damage. e. Value of Public/Nonprofit Services. These data, which are discussed in Chapter 6, page 61, describe the type of services provided, the daily cost of providing these services from this building, the post-disaster continuity premium, and the total value of lost services per day. f. Rent & Business Income. These data, which are discussed in Chapter 6, page 6-14, identify the total monthly rental income and estimated net business income of commercial tenants (if any). g. Mitigation Project Data. These data, which are discussed in Chapter 6, page 6-14, specify the type of mitigation project, lifetime of the project, the total costs, and the effectiveness of the project in avoiding future damages and losses. 5-4 VERSION 1.0 VERSION 1.0 12/29/9412/29/94 B-C PROGRAMS: B-C PROGRAMS: Guidance Guidance I 2. Flood Hazard Data on the "Flood Hazard" data entry screen. The required data on the "Flood Hazard" screen, discussed in Chapter 7, consist of information from the Flood Insurance Study (FIS): flood elevations and discharges for 10-, 50-, 100-, and 500-year floods. If a FIS is not available, then comparable data may be obtained elsewhere or estimated. In any case, good estimates of the flood hazard at the site under evaluation are essential for benefit-cost analysis. LEVEL TWO For large, high-cost projects, projects which are politically sensitive, or (Detailed) projects where initial screening indicates that benefit-cost ratios are B-C Analysis close to one, more detailed analysis may be desirable. Detailed analysis is also necessary whenever the default values, used in the LEVEL ONE (Minimum Data) analysis, do not accurately reflect a specific project under evaluation. See Chapter 8, Benefit-Cost Programs: Level Two Analysis, for detaileddiscussion. The Benefit-Cost Programs allow the user to "override" (i.e., replace) any of the default values by entering building-specific data in the BLUE data entry blocks. All entries in BLUE blocks override default data which are always shown in ORANGE blocks. Users may enter a complete building-specific analysis by entering data in all of the BLUE blocks, or simply enter a few building-specific data where desired. There are several circumstances when entering building-specific data is highly recommended, including: 1. for non-residential buildings, because the FIA depth damage data (see Chapter 6) are predominantly for residential buildings, 2. whenever high water velocities, debris or ice flows are expected during flooding, because the default depth damage data are for damage resulting predominantly from water depth only, 3. for buildings which are unusually susceptible or resistant to flood damage because of construction details or contents, I 5-5 VERSION 1.0 12/29/94 B-C PROGRAMS: Guidance VERSION 1.0 12129/94 B-C PROGRAMS: Guidance I 4. for buildings in which loss of function impacts (relocation costs, rental and business income losses, loss of government services) are high, and 5. any large, high-cost, or politicallysensitive projects, especially when a preliminary LEVEL ONE analysis indicates a benefit-cost ratio near one. R g WAR m Ji~ Xo 1 (nd rforall Expediting Benefit-cost analysis of most common hazard mitigation projects is B-C Analysis easy and simple: many of the required data inputs are built into the software as default values and most of the other required data are readily obtainable. There are data collection requirements necessary in order to conduct benefit-costanalyses. Some data, such as flood hazard information and zero flood depth elevations, are particularly important for the analysis and accurate values must be obtained. Often the necessary data are not particularly difficult to obtain. By providing a quantitative, defensible framework, benefit-cost analysis of hazard mitigation projects may expedite the approval process for good projects by providing solid documentation of eligibility. Benefit- cost analysis may also minimize the appeal process for projects which are rejected by providing quantitative, rather than purely subjective decision-making criteria. Furthermore, if there are disputes between FEMA and applicants over the results of the benefit-cost analysis, all of the input data are clearly on the table for review and discussion. Thus, when the whole project evaluation process is considered, benefit- cost analysis may actually reduce the effort required rather than increase it. Furthermore, there are several ways to conduct benefit-cost analyses efficiently, including: 5-6 VERSION 1.0 12129/94VERSION 1.0 12/29/94 B-C PROGRAMS: GuidanceB-C PROGRAMS: Guidance 1. Use common data to evaluate projects in a single neighborhood. Many of the data may be applicable to numerous structures in a single neighborhood. For example, flood elevations of 10, 50, 100, and 500-year floods may be applicable to an entire neighborhood. Other data inputs such as replacement value per square foot, depth-damage function, etc., may be the same or very similar for many structures in a neighborhood. 2. Evaluate projects in a single neighborhood consecutively. To maximize the use of common data and for consistency, it may be desirable to conduct all the benefit-cost analyses required for a given neighborhood consecutively, changing only the data which differ from project to project. Changes in only a small number of input parameters (or sometimes only one, such as zero flood elevation) may suffice to conduct many analyses, once the first analysis is completed. 3. Group similar projects. If a large number of structures are similar (such as a housing development), then it may not be necessary to conduct individual analyses of each structure. Rather, group projects with the same flood hazard risk (i.e., at the same elevation or closely similar elevations) can be grouped or averaged. A buyout or relocation of one hundred 1,000 square foot houses can be analyzed as 100,000 square feet of single family residences, or analyzed by calculating the benefits for one (average) house, multiplied by one hundred, and then compared to the total cost of the buyout. 4. Consider projects at the same or closely similar, Zero Flood Depth Elevation with the same flood hazard risk. Flood hazard risk will be identical for structures at the same or closely similar Zero Flood Depth Elevation in the same neighborhood. Once the flood hazard information is compiled, many single analyses can be conducted using the flood hazard information, or groups of buildings at the same Zero Flood Depth Elevation can be grouped for one analysis. I 5-7 VERSION 1.0 12/29/94 B-C PROGRAMS: M11idant-A VERSION 1.0 12/29/94 B-C PROGRAMS. Guidnn. If a large number of similar structures at varying elevations are to be evaluated for a buyout, relocation, or S for a single type of flood mitigation measure (e.g., elevation or protection by a levee) then structures may be grouped in bands (contours) of elevation. One or two feet of elevation difference can markedly change flood hazard, so it is very important to only group structures of the same or closely similar elevations. If a large group of structures varies in elevation, the structures may be grouped in one-foot elevation bands: for example, consider all structures between 6.5 and 7.5 feet of elevation to be at 7 feet. Grouping structures in wide bands of elevation (e.g., covering several feet of elevation difference) will almost certainly produce substantially inaccurate results. 5. Use your good judgement and make reasonable estimates. Remember that exact data are generally not available. Always use judgement and reasonable estimates whenever exact data are not available. Although it may be necessary to gather additional data for large (high-cost), controversial, or high-visibility projects, or projects with Benefit-Cost ratios near one, many decisions will be clear-cut and can be made with approximate data only. 5-8 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis CHAPTER 6 PROGRAMS: LEVEL ONE ANALYSISI jBENEFIT-COST Introduction This chapter provides guidance on conducting a LEVEL ONE (Minimum Data) benefit-cost analysis; defines the data input terms; and provides hints on making reasonable estimates when exact data are not available. The LEVEL ONE Data entries MUST be completed whether or not a LEVEL TWO analysis is subsequently conducted. See Chapter 5, Benefit-Cost Programs: Guidance, for general guidance on benefit-cost analysis, including: the use of exact data vs. estimates, when to use LEVEL ONE (Minimum Data) vs. LEVEL TWO (Detailed) benefit-cost analysis, and other helpful hints. See Chapter 3, Program Basics, and Chapter 4, Tutorial, for basic information on moving around within data entry screens, entering data, erasing mistakes, etc. See the Quattro Pro Manual for detailed technical information about the spreadsheet program. DataDifferences:Public, Commercial, & Residential Buildings The Benefit-Cost Programs can be used to evaluate hazard mitigation projects for a wide range of building uses, including public/nonprofit, commercial, residential, and mixed-use buildings. Generally, the data requirements are similar for different building uses. However, any data entries which are not applicable to the building under evaluation may be left blank or zeros may be entered. For example, in a completely public or residential building, leave blank or enter zeros for any entries which pertain to rental or business income. There are six types of avoided damages and losses (i.e., benefits) which are considered in the programs: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. In some circumstances it may not be necessary to consider all of these avoided damages and losses, even if they are applicable to the building under evaluation. 6-1 VERSION 1.0 VERSION 1.0 12/29194 B-C PROGRAMS: Level One Analvsls 12/29/94 B-C PROGRAMS: Level One Analysis If benefit-cost analysis is being used ONLY to establish minimum eligibility for funding and NOT to prioritize projects, then once sufficient benefits are considered to exceed the project costs, it may not be necessary to consider additional benefits. For example, if the benefits of only avoiding building damage exceed costs, then it may not be necessary to consider any of the other damages and losses avoided. If desired, data can be entered sequentially. For example, enter data applicable to building damages only, then review the benefit-cost ratio to see if it is greater than one. If so, then other data entries can be left blank. If not, then contents damage data, displacement costs, etc., can be entered sequentially until benefits exceed costs, i.e., the benefit-cost ratio is greater than one. In other words, it may not be necessary to consider some of the more complicated damages and losses, such as the value of government services lost if projects can be demonstrated to be cost-effective by avoiding only building and contents damages. However, if benefit-cost ratios are used to prioritize among projects with benefit-cost ratios greater than one, then it is important to count fully all of the benefits applicable to each project. Data Input: Color Codes Each entry is color coded. See Cell Colors, page 3-11, or Model I Color Codes on the Benefit-Cost Programs menu. User data entries can be made only in PINK, GREEN, BLUE or RED blocks: PINK BLOCK Information Only: entries do not affect the numerical results; GREEN BLOCK Data Input: entries affect the numerical results; BLUE BLOCK Override Default Values: entries affect the numerical results; RED BLOCK OMB Policy: entries determined by OMB/FEMA policies and affect the numerical results. Blocks colored ORANGE, YELLOW, and PURPLE and all other parts of the programs are protected. User entries cannot be made in these blocks. To change information in PURPLE blocks (Carry Over) the original data entries in the PINK or GREEN blocks must be changed. As you enter data, remember the color codes! 6-2 :VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis FLUisthmi A Introduction To conduct a LEVEL ONE (Minimum Data) benefit-cost analysis, only the LEVEL ONE Data and the Flood Hazard Data must be entered. To conduct a LEVEL TWO (Detailed) benefit-cost analysis, additional building-specific data may be entered. See Chapter 5, Benefit-Cost Programs: Guidance, for a discussion of the differences between LEVEL ONE and LEVEL TWO analyses. See Chapter 8, Benefit- Cost Programs: Level Two Analysis, for a detailed review of conducting a LEVEL TWO analysis. Me1 I Sm These data entries describe the building and hazard mitigation project under evaluation. Building Name Address City, State, Zip PINK Blocks (Information Only). These entries contain basic identifying information about the building being evaluated: Building Name, Address, City, State and Zip Code. Help When entering the address (or any combination of letters and numbers which begin with a number), remember to first type an apostrophe (') followed by the number and street name. See Chapter 3, page 3-13. Owner PINK Block (Information Only). The building's Owner may be an agency, a private party, etc. Building ownership may affect eligibility for hazard mitigation funding. 6-3 VERSION 1.0 12/29/94 B-C PROGRAMS, Level One Analysis Contact Person Disaster Number Project Number Application Date Discount Rate (%) PINK Block (Information Only). The Contact Person is someone who could, if needed, provide additional information about the building to the analyst. PINK Block (Information Only). The Disaster Number is a unique number assigned by FEMA for each disaster. PINK Block (Information Only). The Project Number may be the DSR number assigned by FEMA or any other identifying number. PINK Block (Information Only). The Application Date is the date when the application was submitted to FEMA. RED Block (OMB Policy). The Discount Rate entry is determined by OMB/FEMA policy and cannot be varied by the user on a project-byproject basis. On October 29, 1992, OMB issued Circular A-94, Revised (Transmittal Memo No. 64), "Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs." In this Circular, OMB states that the appropriate discount rate varies depending on whether or not the investment (i.e., project) is an "internal Federal government investment." For FEMA-funded hazard mitigation projects for state and local governments (or eligible nonprofits), the OMB-mandated discount rate is the rate applicable for investments which are not internal Federal government investments. The OMB-mandated discount rate corresponds approximately to the 30-year Treasury bond rate, but the appropriate rate is specifically fixed by OMB annually. Currently, the OMB-mandated discount rate is 7% (see Appendix C of Circular A-94). For each disaster, an appropriate discount rate should be determined by FEMA, in accordance with the OMB guidance, and applied uniformly to all hazard mitigation projects being considered. The discount rate determined for each disaster is entered in the RED Block. After this rate is determined and entered ONCE, it can then be used for analysis of ALL hazard mitigation projects for this disaster. 6-4 VERSION 1.0 12129194 B-C PROGRAMS: Level One Analysis Scenario Run ID PINK Block (Information Only). The Scenario Run ID provides a place to enter a Run Number or identifying name to distinguish this particular benefit-cost analysis from others. In some cases, multiple analyses of the same project may be run with different sets of input assumptions to explore the sensitivity of results to changes or uncertainties in input data. Analyst PINK Block (Information Only). The Analyst block identifies the person principally responsible for the benefit-cost analysis. The analyst's name is displayed automatically in small type on the bottom of each printed page and on the cover page of the printed report. II L =_11]I BUILDING TYPE The building's construction type is very important for the benefit-cost analysis because many of the numerical values in the programs, including the amount of damage a particular building type is expected to sustain under different flood depths, depend on the building type. GREEN Button (Data Input). Select the Building Type by clicking on the appropriate green and gray button which applies and determines many of the default parameters. The selected building type appears in the purple cell labeled "Building Type Selected." l~~~~~~~~, _-X MANSX ORSt~ ffiff'.'i>R4mmet -I-,~ 11---_ .<1 4 _ I I I --,X,,<....... 'ev. | _~~~~~~~1= ,9..-,:i _ ,.' St.>t-'2:. 8 , 18.f,Totat~Buildng t ($n).e Repaceme valu 6-7 VERSION 1.0 12/29/94 B-POGAS:Lee O gnenls' VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis Building Replacement Value ($Isf) Total Building Replacement Value Demolition Threshold GREEN Block (Data Input). Building Replacement Value ($Isf) is a measure of the economic value of the building, including the structural and non-structural permanent parts of the building, but excluding contents. Replacement value means the cost to provide a functionally-equivalent structure of the same size. Replacement value does not include recreating historical or archaic materials, finishes or features. For historic buildings, the distinction between "reproduction" and "replacement" value may be important. Reproduction duplicates the design and architectural details of a specific building. For historic buildings, the reproduction value rather than the replacement value may be a more appropriate measurement of a building's value. If desired, an historic building's reproduction value (in $Isf) can be entered in the "Building Replacement Value" block. YELLOW Block (Result). Total Building Replacement Value ($)is calculated from the value per square foot and the building size. GREEN Block (Data Input). Building Damagethat would Result in Demolition, the "demolition threshold," is the percentage of building damage at which demolition and replacement (rather than repair) would 0 be expected to occur as the economically efficient choice. Many buildings will be demolished rather than repaired when the cost to repair the damage exceeds some percentage of the replacement cost. I ~ A For older, somewhat substandard buildings, the demolition threshold may be quite low (e.g., 20 or 30%). For typical, relatively modern buildings, the threshold will generally be higher (e.g., 50 or 60%). For some particularly important historical buildings, the demolition threshold may approach 100%. 6-8 VERSION 1.0 i12/29/94 B-C PROGRAMS: Level One Analysis The demolition threshold damage percentage is an important policy parameter which may significantly affect the benefit-cost results because it may have a major impact on the depth-damage function. Therefore the demolition threshold damage percentages should be chosen carefully in accord with the condition and viability of the existing building. For example, a brand new city hall building would probably be repaired from a higher level of damage than would a decrepit building badly in need of refurbishing. YELLOW Block (Result). The demolition threshold in dollars of damage is calculated from the entered percentage and the building replacement value. 3 S~~~~ : Contents PINK Block (Information Only). The Contents Description block is Description for a brief summary of the building's contents (e.g., computers, office furniture). Total Value of GREEN Block (Data Input). -Total Value of Contents is the estimated Contents total value of the building's contents, including furniture, carpet, equipment, computers, supplies, etc. The exact value of building contents is rarely known. Estimates can be obtained from owners, or from a general knowledge of the nature of the contents and common sense. For example, an art museum or a building filled with computers will have a much higher contents value than a building storing used bricks or recycled newspapers. For most buildings, the value of contents is significantly smaller than the building value. However, in some cases where contents are unusually valuable (e.g., an art museum) or usually vulnerable to flood damages, then avoiding contents damage may be as important or more important than avoiding building damages in determining total project benefits. Default estimates of the Contents Depth-Damage Function (i.e., contents damage as a percentage of total contents value) are based on the building type selected. To view the default contents depth-damage function for the building type selected, choose Level Two Data I Contents Depth-Damage Function from the Benefit-Cost Program menu; for more information see page 8-8. 6-9 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis Value of Contents ($/sf1 Rental Cost of Temporary Building Space ($/sf/month) RentalCost of Temporary Building Space ($/month) Other Displacement Costs Total Displacement Costs YELLOW Block (Result). The Value of Contents ($Isf) is calculated from the Total Value of Contents and the Total Floor Area of the building. The Value of Contents ($/sf) may be useful in comparing contents values from building to building and as a guide as to whether estimated contents values are reasonable. 3 A S 3 0 0033k O Displacement Costs due to Flood Damage may be incurred when owners must operate from a temporary site while flood-related damage to the original building is repaired. Costs for temporary rent and other displacement expenses are entered here. GREEN Block (Data Input). Rental Cost of Temporary Building Space ($lsflmonth) is an estimate of the rental rate paid for temporary quarters. Major floods may cause extensive damage to many structures, thus reducing the available supply of alternate space and leading to higher rental costs throughout the area. YELLOW Block (Result). The Rental Cost of Temporary Building Space ($lmonth) is calculatedfrom the Area Occupied by Owner or PubliclNonprofit Agencies (sf) and the Rental Cost of Temporary BuildingSpace ($1sf/month). GREENBlock (Data Input). Other Costs of Displacement ($/month) include moving and extra operating costs incurred because of the disruption and displacement from normal quarters. YELLOW Block (Result). Total Displacement Costs ($/month) are calculatedas the sum of Rental Cost of Temporary Building Space ($Imonth) and Other Costs of Displacement ($/month). Default estimates of displacement times depend on building damages at each flood depth. To view the default displacement time estimates choose Level Two Data I Displacement Time from the Benefit-Cost Program menu. For more inforniation, see page 8-11. i 6-10 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis Description of Services Provided Annual Budget Displacement costs for tenants are approximated in the programs by counting the rental income losses to the owner. Counting tenant displacement costs and rental income losses would be double counting. For public/nonprofit agencies, Displacement Time is distinct from Functional Downtime (i.e., service interruption); estimates for each will generally be quite different. For example, a public agency which is relocated in temporary quarters for six months will incur six months of displacement costs, but the loss of service is only two weeks if the agency is functioning in temporary quarters two weeks after the flood. To view the Default Functional Downtime estimates, choose Level Two Data I Functional Downtime from the Benefit-Cost Program menu; or see page 8-14. l * a S * I The value of public/nonprofit services is included in the benefit-cost programs to count fully the benefits of avoiding flood damage for such facilities. If the building under evaluation is a commercial or residential building, then leave these entries blank or enter zeros. PINK Block (Information Only). This block provides a place to enter a brief summary of the type of services provided from this location. GREEN Block (Data Input). The Annual Budget of Public/Nonprofit Agencies is the total annual operating budget of all the public/nonprofit agency functions located in this building. The total should include rental costs but exclude "pass-through" monies (e.g., Social Security payments) which the agency receives and redistributes. The annual operating budget is used to estimate the value of services provided. For example, if a public/nonprofit Egency spends $10,000 per day 6-11 VERSION 1.0 012/29/94 :7I ; B-C PROGRAMS: Level One Analysis VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis providing a service to the public, then this service is valued at $10,000 per day and the loss of this service due to flood damage is also valued at $10,000 per day. Is Rent GREEN Buttons (Data Input). Select whether the Annual Budget Included? includes or excludes any rent paid (by an agency which does not own the structure) by clicking on the appropriate button. Your choice willbe displayed next to the rent buttons. Proxy Rent ORANGE Block (Default). If rent is NOT included in the annual budget, the programs calculate a default or proxy rent based on the value of the building and the discount rate. User-Entered BLUE Block (Override Default). Enter a User-Entered Rent Rent Estimate Estimate ($Imo) in place of Proxy Rent if the proxy rent displayed is not an accurate estimate for the building under evaluation. Cost of YELLOW Block (Result). The programs calculate the daily Cost of Providing Providing Services from this Building ($/day)based on the annual Services budget and, if rent is not included in the annual budget, from the default proxy rent or, ifprovided, from the user-entered rent estimate. Post-Disaster GREEN Block (Data Input). Some public/nonprofit services may be Continuity very littlein demand after a disaster, while others may be vital to Premium maintain. Public/nonprofit services that are important for post-disaster response and recovery are worth more to the community after the disaster than in normal circumstances. The Post-Disaster Continuity Premium ($/day) is a way of assigning an extra value to these post- disaster services. For example, emergency services would be vital in the hours and days immediately followinga disaster, whereas routine services such as employment referral would not. Based on the nature of the services in this building, the continuity premium is how much extra daily cost the tenant agencies would be willing to spend to maintain agency functions after a disaster. The magnitudeofthe Post-Disaster Continuity Premium depends on how critical the services are in the post-disaster environment. Emergency response services such as medical, fire, and police are particularly important post-disaster and continuity premiums for such services are generally high. Services which are only moderately important post-disaster should have moderate premiums. Routine services that can be delayed with littleor no impact should not have continuity premiums. 6-12 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis Continuity premiums of 50-100% of the normal daily costs of providing services may be appropriate for services which are moderately important in the post-disaster environment. Continuity premiums of several times normal daily costs may be appropriate for emergency response services. Continuity premiums of five or ten times the normal daily costs may be appropriate for services which are critical to the disaster response. The Post-Disaster Continuity Premium, like all other inputsfor the benefit-cost analysis, must be reasonable and defensible for the specific public/nonprofit service being valued. If the continuity premium is unreasonable, this portion of the analysis will be invalid. Total Value of YELLOW Block (Result). TheTotal Value of Lost Services ($/day) Lost Services is calculated by summing the daily cost of providing services under normal conditions and the Post-Disaster Continuity Premium. Estimates for the value of lost public/nonprofit services for each flood depth are based on the daily cost of providing services and estimates of Functional Downtime. Functional Downtime is the time period for which public/nonprofit services are lost due to flood damage. Default estimates of Functional Downtime are based on the building depth- damage function. To view the default Functional Downtime estimates choose Level Two Data I Functional Downtime from the Benefit-Cost Program menu; or see page 8-14. 6-13 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis IV * mF11 0I-1 I .8'.C: 1''9fv.A'... :'.''sR . g X->t'o.Gs'SKwiS1O.-^' '-y S ;'A::' :.'. ->S S Gal~ MoiithlRent from All~isth >:enatws, stm'ate'dNet T yf (S,>mahl m hl | l- Icoe iCommrc~EBisnesesrrS Hi Total Monthly GREEN Block (Data Input). Total Monthly Rent ($/month) entered Rent From All here is the amount paid by all tenants in the structure. For a Tenants commercial or residential building which is rented, this amount is included to value the loss of rental income from flood damages. For a public/nonprofit building, the rent value entered should be only the rent for that portion, if any, rented to private tenants. Rent costs for public/nonprofit agencies are included in the Value of PubliclNonprofit Services section discussed above. Estimated Net GREEN Block (Data Input). Estimated Net Income of Commercial Incomeof Businesses ($/month) is the net, not gross, income per month of Commercial commercial businesses in the building. Exact figures will generally not Businesses be available, so reasonable estimates may be made. If there are no commercial businesses in the building, then leave this entry blank or enter a zero. 011M * snSNli Select Mitigation Measure Select Mitigation Measure GREEN Buttons (Data Input). Select the mitigation measure by clicking on the appropriate green and gray button. The selected mitigation measure appears in the purple cell labeled "Type of Mitigation Selected." 6-14 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis VERSION 1.0 12129/94 B-C PROGRAMS: Level One Analysis Project PINK Block (Information Only). This space is provided to enter a Description brief summary of the proposed mitigation project, for example, "buyout," "relocate," or "elevate ten feet." Project Useful GREEN Block (Data Input). The project's useful life is the estimated Life number of years during which the mitigation project will maintain its effectiveness. Useful life is the time period over which the estimated economic benefits of the proposed mitigation project are counted. The useful life which the user enters MUST be commensurate with the actual project being considered. Useful lives of 5 to 10 years for equipment purchases, and 30 (residential) to 50 (non-residential) years for building projects are typical. For major infrastructure projects, or for historically important buildings, useful lives of 50 to 100 years may be appropriate. For buyouts/relocations an entered lifetime of 100 years will capture fully the benefits of the mitigation measure. Mitigation Effectiveness Estimates GREEN Block (Data Input). The effectiveness of most flood mitigation projects varies with the depth of flood water. For the flood mitigation type selected, enter estimates of the depth at which the mitigation is 100% and 0% effective: Elevation Elevating buildings by N feet is generally 100% effective to N-1 feet. For example, elevating 8 feet is 100% effective to 7 feet, elevating 12 feet is 100% effective to 11 feet. This result arises from the fact that, for example, an "8-foot flood" is considered in the programs to be all floods between 7.5 and 8.5 feet. Therefore, elevating a structure 8 feet will convert an 8foot flood into a 0-foot flood (from -0.5 to 0.5 feet), and there is still damage from a 0-foot flood. Thus, an 8-foot elevation is 100% effective to only 7 feet. 6-15 B-C PROGRAMYS: Level One Analysis VERSION 1.0 12/29/94 AayiVERSION-1.--22/9 RORM:Lee-n For buildings with basements, the situation can be more complicated depending on the degree of flood proofing of the basement. Unless there is detailed information available aboutan individual structure, assuming that elevating N feet is 100% effective to N-1 feet is a reasonable assumption for structures with and without basements. This assumes that flood proofing of the basement occurs along with elevation. The flood depth at which elevations are 0% effective is calculated automatically by the programs and need not be entered by the user. Relocation/Buyout Relocation/Buyout projects are assumed to be 100% effective at all flood depths and thus effectiveness depths need not be entered by the user. Flood Barriers The flood depth at which flood barriers are 100% and 0% effective depends on how the barrier is constructed and on assumptions about freeboard. Freeboard is defined as the height of a flood barrier above a flood height which is necessary to insure satisfactory flood performance. For example, to provide 100-year flood protection for flood insurance purposes levees must be constructed 3 feet above the 100-year flood elevation (i.e., with 3 feet of freeboard). In the absence of detailed engineering analysis, a simple assumption about flood barriers is that a flood barrier of height N feet is 100% effective to N-1 feet and 0% effective at N feet. Other Other flood hazard mitigation projects include wet flood proofing and any other measures not covered by the three mitigation types discussed above. The depths at which "Other" flood hazard mitigation projects are 100% and 0% effective must be estimated on a case-by-case basis. The programs calculate effectiveness only for the selected mitigation project type. Other entries should be deleted (see Delete button, page 3-13) to avoid confusion; however, the programs ignore any other values in the table. I 6-16 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis MITIGATION PROJECT COSTS Project Cost Base Year of Costs Annual Maintenance Costs Present Value of Annual Maintenance Costs Relocation Costs for Mitigation Project The effectiveness of flood hazard mitigation projects at every flood depth is calculated by the programs from the depths of 100% and 0% effectiveness. To view the default Mitigation Effectiveness estimates at each flood depth select Level Two Data I Mitigation Project Effectiveness from the Benefit-Cost program menu; for more information see page 8-17. GREEN Block (Data Input). The Mitigation Project Cost includes all direct construction costs plus other costs such as architectural and engineering fees, testing, permits, and project management, but excludes relocation costs. PINK Block (Information Only). The Base Year of Costs is the year in which the mitigation project's costs were estimated. If cost estimates are several years old, they may need to be adjusted by the user to account for inflation in costs between the base year and the present. GREEN Block (Data Input). Annual Maintenance Costs ($/year) may be required to maintain the effectiveness of some mitigation projects, particularly levees where annual inspection and vegetation removal may be required. For most other mitigation projects, Annual Maintenance Costs will be negligible or zero. YELLOW Block (Result). Based on the discount rate, the Annual Maintenance Cost for each year of the project's useful life is reduced to its present value and summed. For some mitigation projects, occupants may have to be relocated for construction of the project. In such cases, the Relocation Costs are an integral part of the mitigation project and must be counted in the total mitigation project costs. 6-17 VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis VERSION 1.0 12/29/94 B-C PROGRAMS: Level One Analysis Relocation Time Due to Project Rental Cost During Occupant Relocation Other Relocation Costs Total Relocation Costs Total Mitigation Project Costs To Continue... GREENBlock (Data Input). Relocation Time Due to Project (months) is the number of months for which the building must be vacated in order for the mitigation project to be completed. Note that this relocation time is completely distinct from the displacement time needed to repair flood-related damages. GREEN Block (Data Input). Rental Cost During Occupant Relocation ($/sf/month) is an estimate of the rental rate paid for temporary quarters. Major coastal floods may cause extensive damage to many structures, thus reducing the available supply of alternate space and leading to higher rental costs throughout the area. YELLOWBlock (Result). Rental Cost During Occupant Relocation ($/month) is calculatedfromthe Rental Cost ($lsflmonth) and the Total Floor Area (sf). GREENBlock (Data Input). Other Relocation Costs ($/month) include moving and extra operating costs incurred because of the temporary relocation. YELLOWBlock (Result). The Total Relocation Costs are calculated fromthe entered Relocation Time Due to Project (months), Rental Cost During Occupant Relocation ($/month), and Other Relocation Costs ($/month). YELLOWBlock (Result). Total Mitigation Project Costs are calculated by summingthe Mitigation Project Cost, the Present Value of the Annual Maintenance Costs, and the Total Relocation Costs. This completes the LEVEL ONE (Minimum Data) Benefit-Cost Analysisdata entry process except for the Flood Hazard data. To enter Flood Hazard data, click on the Next Screen button at the bottom of the second LEVEL ONEData page, or select Flood Hazard from the Benefit-Cost Program menu. 6-18 VERSION 1.0 12129/94-B-C PROGRAMS: Flood Hazard Risk : -CHAPTER 7 BENEFIT-COST PROGRAMS: FLOOD HAZARD RISK Introduction This section contains data entries for flood frequencies, discharges and elevations which are necessary to specify quantitatively the extent of flood hazard at the site under evaluation. From the entered flood data, the programs calculate the expected annual number of floods in one- foot elevation increments. "Expected" annual number means the long term statistical average number per year, not that this number of floods occurs every year. The degree of flood risk at a particular site profoundly affects the expected flood damages at a site and thus profoundly affects the benefits of avoiding flood damages at the site. Therefore, the flood hazard data entered in this section are among the most critical data inputs for benefit-cost analysis of flood hazard mitigation projects. LEVEL ONE A LEVEL ONE Flood Hazard Risk Analysis is performed using Analysis Information from a FIS and a FIRM, or equivalent information, for the location under evaluation. Data on flood frequencies and elevations are entered into the Flood Data table shown on page 7-2. LEVEL TWO Analysis If a FIS and a FIRM are not available, or if the user desires to use other estimates of flood hazard risk, then a LEVEL TWO Analysis must be performed. 7-1 VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk A AW9 m Carry Over PURPLE Blocks (Carry Over). Information from the LEVEL ONE Information DATA page is displayed to identify the building under consideration and to provide reference information and guidance for LEVEL TWO (Detailed) evaluations. **9 AU9 A - A *A I Flood Data Flood frequency, discharge and elevation data MUST be entered in the flood hazard table in order to calculate the degree of flood risk at the site under evaluation. Flood data for 10-, 50-,100-, and 500-year floods are generally available from the Flood Insurance Study (FIS) for the area under evaluation. However, if flood data for other frequencies are available, the frequencies and corresponding discharge and elevation data may be entered in this table. The table showing the expected annual number of floods is automatically recalculated whenever the flood data are revised. Flood Discharge The FIS contains a table of flood frequencies and discharges similar to Data the two left hand columns of the table above. If more than one set of discharge data are shown for the stream, use the discharges for the closest location downstream from the building location. Flood Elevation The FIS also contains Flood Profile graphs which show the elevations Data of 10-, 50-, 100-, and 500-year floods along the stream. The elevation of a 100-year flood, for example, varies with location along the stream because water runs downhill. To characterize flood risk at a given location, it is necessary to know the elevation of the 10-, 50-, 100-, and 500-year floods at this location. These data may be obtained from the Flood Profile graphs in the FIS. I 7-2 VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk Flood Profile graphs show the variation of flood elevations with distance * X f . upstream from a waterway confluence, bridge, or street crossing. To : :: . determine the elevations for the building under evaluation, the distance upstream from a landmark on the Flood Profile graph must be measured on a map. The Flood Insurance Rate Map (FIRM) may be used for this purpose. Once the location has been properly identified, then flood elevations for 10-, 50-, 100-, and 500-year floods are read from the Flood Profile graph. An example of a Flood Profile graph from an FIS is shown on the following page. In this example, stream distance is shown in thousands :: of feet above the confluence with Overpeck Creek. The house under ,: evaluation is located about 7850 feet above the confluence, or 45 feet upstream from Vanostrand Avenue overcrossing. Flood, elevations for the 10-, 50-, 100-, and 500-year floods are read from this section of the Flood Profile graph. In this example, the 500-year elevation is 128.1 feet; the 100-year . . elevation is 127.1 feet; the 50-year elevation is 125.9 feet; the 10-year elevation is 124.5 feet; and the channel bottom is 119.5 feet. See the Flood Profile graph on the next page. Flood elevations may vary markedly along the stream course, depending on the gradient of the individual stream. Therefore, it is very important to read properly the flood elevation data on the Flood Profile graph for the specific site under evaluation. I ..; 7-3 mni Co 125 _ FD 120 mxA) -L ID 3 115 m l-3 N) -'I z , 0n -w C)0r CO, 110 -I a 025 X 105 - 0 00.N ma) 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.0 8.1 3 -w STREAMDISTANCEIN THOUSANDSOF FEET ABOVECONFLUENCEWITHOVERPECKCREEK 0. 0 0 VERSION 1.0 12i29/94 B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk eeaA TA0A I A~~~~9 I NAIA Flood Data Flood frequency and elevation data MUST be entered in the flood hazard table in order to calculate the degree of flood risk at the site under evaluation. Flood data for 10-, 50-, 100-, and 500-year floods are generally available from the Flood Insurance Study (FIS) for the coastal floodplain area under evaluation. However, if flood data for other frequencies are available, the frequencies and elevation data may be entered in this table. The table showing the expected annual number of floods is automatically calculated whenever any of the screens which display results calculated from these flood data. However, to view the expected annual number of floods before going to results, the Update Flood Data Button must be clicked to run the regression calculation which provides the expected annual number of floods estimates. Flood Elevation The FIS usually contains tables which show the elevations of 10-, 50-, Data 100-, and 500-year floods. Unlike riverine floods, where flood elevations vary with distance along the stream, coastal floods are assumed to be at the same elevation throughout an area to which a particular transect or a group of transects applies. A transect (see Figures 7-2 and 7-3) is a line drawn perpendicular to the coastline showing the A-Zone and V-Zone regions. Thus, if a 1 00-year flood has an elevation of 6.5 feet, this elevation applies along the transect as shown in the FIS. The "1-year" flood elevation data entry can be estimated from the highest expected annual tide level or from other local flood gauge data. The flood frequency and flood elevation data are very important for the benefit-cost analysis and accurate data from a FIS or other reasonable estimates must be entered in the Flood Hazard Table. I 7-5 VERSUION1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk For additional guidance on obtaining flood information from Flood Information Studies and Flood Insurance Rate Maps, users are referred to the following publications: 1. Guide to Flood Insurance Rate Maps (FIA-14), FEMA, May, 1988. 2. Flood Proofing, How to Evaluate Your Options, U.S. Army Corps of Engineers, 1993. 3. Flood Retrofitting Manual, FEMA, 1994. 7-6 m 0 z MB CD A ZONE | V Z0O E LWAVEHEIGHT X WAVE HEIGHT GREATER THAN 3FT. t BASEFLOODELEVATION INCELUDINGWAVE EFFECTSS aC) 0f _l~~MEAN ~~~~~~~~~~~~~~~~~~~~~~~~ -'I G) FEC AN WAET w~~~~~~~~~~~~~~~~WN C) 0 0 en ent: Wave x~~~~~~~~~~~NDWAE Source: Flood Insurance Study Suppleent W e Height Analysis 5. T0 FEMA, 1983. Pr m CO 0 7I3 _ C)~~~~~~~~~~~~~~)' 0_ .I i O rn -4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FERCHARLOTTE COUNTY, FL Ad0..0f TRANSECTLOCATIONMAP:I 16 E ---. 0 _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l .I CO) l~ Source: Flood Insurance Study Supplement: Wave Height Analysis _-MA, 1983. VERSION 1.0 12/29194 B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk ~ ~ i A : ;:' ~ RUJA~ ff*,749X01:1#XA~~~~~~~~~~~~~~~~ Expected Annual Numberof Floods by Flood Depth Default Flood The default estimates of the Expected Annual Number of Floods of Estimates each flood depth from -2 to 18 feet are shown in the ORANGE (Default) column. These estimates are calculated from the flood frequency, discharge and elevation data entered previously. "Expected annual number" of floods does not mean that this number of floods occurs every year, but rather "expected" indicates the long term statistical average number of floods per year. The default estimates of the expected annual number of floods at each depth are shown in scientific notation because these numbers may vary over an extremely wide range, including very small numbers. For an explanation of scientific notation, see the Technical Appendix to this chapter, page 7 12. Except when annual probabilities approach one, the expected annual number of floods and the annual probability for each flood depth are virtually identical. i For a LEVEL ONE analysis, these default estimates of the expected annual number of floods at the site under evaluation should be used. 7-9 VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard RIRk User-Entered If desired, user-entered estimates of the annual probabilities of floods of Flood Estimates each flood depth can be entered in the BLUE (Override Default) column of the Flood Hazard Table. Making such estimates and other possible modifications of the default flood estimates are discussed below in the Level Two Flood Analysis section. LEVEL TWO There are two ways to conduct a LEVEL TWO Flood Hazard Risk Flood Analysis Analysis: 1. The flood data entry table (above) can be filled in with estimates based on limited data or informed judgement. Such an analysis will be less accurate than analyses using full FIS/FIRM (or equivalent) data, but flood estimates will be approximately correct as long as the input estimates are reasonable for the area under evaluation. Such an analysis is a LEVEL TWO analysis because it requires interpolation or extrapolation of limited data and/or other professional judgement about flood risks. 2. The default values of the Expected Annual Number of Floods for each flood depth can be overridden with user- entered estimates. This option requires an independent source of flood data, such as a U.S. Army Corps of Engineers study or other data from a professional hydraulics engineer experienced in flood modeling. Such flood data MUST be expressed as Expected Annual Numbers of Floods at the appropriate location and elevation under evaluation. To override the default estimates in the ORANGE column, user-entered values are entered in the BLUE column. Whenever user- estimates of the expected annual number of floods are entered, the programs use these values rather than the default values, although the default values are displayed for comparison to the user-entered values. 7-10 VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk Flood Hazard Risk: Technical Appendix Flood Recurrence Intervals Flood Elevation vs. Flood Depth Floods are a probabilistic natural phenomenon: it is impossible to predict in what years floods will occur or how severe the floods will be. Flood hazards are often expressed in terms of flood frequencies or recurrence intervals, such as a 1 0-year flood or a 1 00-year flood. A "100-year" flood means that there is a 1 % chance per year of a flood at the 1 00-year or higher flood elevation. A 1 0-year flood means that there is a 10% chance of a flood of the 1 0-year or higher flood elevation. In general, the annual probability of a flood of X-years is 11X. Thus, the annual probability of an 83-year flood is 1/83 or 0.012. Flood recurrence intervals do not mean that floods occur exactly at these intervals; rather they only express the probabilities of floods. Thus, a given location may experience two 100-year floods in a short time period or go several decades without experiencing a 10-year flood. Flood recurrence intervals (in years) and annual flood probabilities contain exactly the same probabilistic information. The previous paragraphs explained how to convert recurrence intervals in years into annual probabilities. Conversely, annual probabilities can be converted to recurrence intervals. The recurrence interval in years of a flood depth with Y annual probability is 1N. For example, the recurrence interval for a flood with an annual probability of 0.01234 is 1/0.01234 or 81 years. In the benefit-cost programs, flood probabilities are expressed in terms of annual probabilities. If desired, these probabilities can be converted to recurrence intervals by the procedure discussed above. For a given Riverine Flood (e.g., a 100-year flood), the elevation of the flood water surface varies with location along the stream as shown by the Flood Profile (see pp. 7-2 to 7-4). For a given Coastal Flood (e.g., a 1 00-year flood), the elevation of the flood water surface is approximately constant along a given transect (see pp. 7-5 to 7-7). At a given location the flood depth corresponding to a 1 00-year flood varies depending on the Zero Flood Depth Elevation of the building under evaluation. In the Benefit-Cost Programs, Expected Annual Numbers of Floods are shown for each flood depth from -2 to 18 feet for the building under evaluation. For a different building with a different Zero Flood Depth Elevation, the Expected Annual Number of Floods for each flood depth will be different. Thus, for example, the depth of a 1 00-year flood will differ for buildings at different Zero Flood Depth Elevations. I 7-11 VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12129/94 B-C PROGRAMS: Flood Hazard Risk Review of The annual probabilities of floods are expressed in scientific notation Scientific because the probabilities may vary from nearly 1 to much less than 1 in Notation a million (0.000001). Scientific notation is a widely-used convenient method of expressing numbers which vary over a very wide range. In scientific notation, as in the Calculated Annual Probability of Floods table, numbers are expressed in two parts: a prefix and a power of 10. For example, 6E+02, where 6 is the prefix and +02 is the power of 10, means 6 times 102, or 6 times 100, or 600. Another way of thinking about scientific notation is that the power of 10 part of the number tells which direction and how much to move the decimal place. Thus, 6E+02 is 6 with the decimal placed moved to places to the positive (right) direction or 600. Thus, 6E+03 is 6000. Scientific notation with negative powers of ten, means to move the decimal place to the negative (left) direction. Thus, 6E-02 is 0.06; 6E 03 is 0.006 and so on. E+00, means don't move the decimal place. Thus, 6E+00 is simply 6. Scientific notation may seem cumbersome with routine numbers, but it is very convenient when numbers are very large or very small or to compare the relative sizes of very large or small numbers. Thus, 6E11 is a more convenient way of expressing 0.00000000006. Flood The Expected Annual Numbers of Floods for each flood depth, Exceedance correspond closely to Annual Probabilities of floods. Such probabilities Probabilities are interval probabilities; that is, they express the probabilities for each flood depth. For example, in the Benefit-Cost Programs, the annual probability of a 2-foot flood is considered to be the annual probability for all floods between 1.5 and 2.5 feet of depth at that site. Flood probabilities are often expressed as exceedance probabilities. An exceedance probability means the probability of all floods greater than or equal to some specified flood. Thus, the annual exceedance probability for a 2-foot flood means the annual probability for all floods greater than or equal to 2 feet. To avoid confusion, the distinction between interval probabilities and exceedance probabilities must be clearly made. The commonly used term 1 00-year flood, is actually an exceedance probability. In other words, the 100-year flood level with an annual probability of 0.01 means all floods greater than or equal to this level. The interval probability of a flood at exactly (within plus or minus 0.5 feet) the 1 00-year flood level will be smaller (sometimes much smaller) than the exceedance probability for a 1 00-year flood, because the exceedance probability includes ALL floods greater than or equal to the 1 00-year flood. 7-12 :-VERSION 1.0 12/29194 -B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk For completeness, the benefit-cost programs tabulate both exceedance probabilities and interval probabilities, although all calculations are done using the interval probabilities. Graphs of flood probabilities (both exceedance and interval) may be viewed by clicking on the graph buttons at the end of the flood hazard screen in the Benefit-Cost Programs. Expected The Riverine Flood modeling uses an approach outlined by the U.S. Annual Number Army Corps of Engineers for riverine flooding (Flood Proofing, How to of Floods-Evaluate Your Options, 1993). Riverine The Expected Annual Number of Floods at each flood depth are calculated from the flood frequency and flood elevation data entered by the user, along with the Zero Flood Depth Elevation of the building under evaluation. The flood frequency data (i.e., 10, 50, 100, or 500 years) correspond to exceedance probabilities (see Flood Recurrence Intervals section on page 7-7). The computer program does a regression analysis fit between the logarithm of exceedance probability and flood discharge to obtain a smooth curve relating exceedance probability and flood discharge. Then, flood elevations are read (by the program) from the "rating curve," which is the relationship between flood discharge and elevation. The regression analysis is done in this manner because the relationship between stream discharge and probabilities is smooth whereas the relationship between flood elevation and probabilities may be very irregular because of variations in stream valley shape. Flood probabilities for floods below the 10-year flood elevation are determined using the standard A-1 to A-30 flood curves used previously on FlRMs. This analysis gives the annual exceedance probability for all floods, in one-foot increments of depth. From the annual exceedance probabilities, calculated as described above, the expected annual number of floods in a given one-foot increment are calculated from the difference in exceedance probabilities of two flood depths. For example, the expected annual number for a 2-foot flood (i.e., all floods between 1.5 and 2.5 feet) at a given site (with a given Zero Flood Depth Elevation) is calculated as the exceedance probability for a 1.5-foot flood minus the exceedance probability tor a 2.5-foot flood. I 7-13 VERSIONA1.0 12/29194 B-C PROGRAMS: Flood Hazard Risk VERSION 1.0 12/29/94 B-C PROGRAMS: Flood Hazard Risk Expected The Coastal A-Zone flood modeling uses an approach similar to that Annual Number outlined by the U.S. Army Corps of Engineers for riverine flooding of Floods -(Flood Proofing, How to Evaluate Your Options, 1993). Coastal A-Zone Coastal A-Zone flood models are based on storm surge models which predict flood elevations. Depending on the date of the Flood Insurance Study, various elevation standards may be used in the FIS (e.g., National Geodetic Vertical Datum of 1929, NGVD or others). Regardless of the elevation standard used, the FIS always gives flood elevations relative to some benchmark elevation. The Expected Annual Number of Floods at each flood depth are calculated from the flood frequency and flood elevation data entered by the user, along with the Zero Flood Depth Elevation of the building under evaluation. D&>f6bmFlood 1nsau FIS od Inrce' RatekM' Xm MA F1 "1W The flood frequency data (i.e., 10, 50, 100, or 500 years) correspond to exceedance probabilities (see Flood Recurrence Intervals section on page 7-7). The computer program does a regression analysis fit between the logarithm of exceedance probability and flood depth to obtain a smooth curve relating exceedance probability and flood depth. This regression fit gives the annual exceedance probability for all floods, in one food increments of depth. From the annual exceedance probabilities, calculated as described above, the expected annual number of floods in a given one foot increment are calculated by difference.. For example, the expected annual number of a 2-foot flood (i.e., all floods between 1.5 and 2.5 feet) is calculated as the exceedance probability for a 1.5-foot flood minus the exceedance probability for a 2.5-foot flood. For a given coastal area covered by a FIS and a FIRM, the elevations of the 10-, 50-, 100-and 500-year floods are constant over the entire area. However, the probability of a given flood depth occurring at a specific site depends very strongly on the elevation of the particular site. Thus, the Zero Flood Depth Elevation of the facility underevaluation has a profound impact on the degree of flood risk experienced at the site. 7-14 VERSION 1.0 12/29/94 LEVEL TWO: Introduction CHAPTER 8 BENEFIT-COST PROGRAMS: LEVEL TWO ANALYSIS Introduction Chapter 6, Benefit-Cost Programs: Level One Analysis, reviewed the data entries necessary to conduct a LEVEL ONE (Minimum Data) Benefit-Cost Analysis, relying heavily on default values built into the programs. This chapter provides guidance on LEVEL TWO (Detailed) analyses which may incorporate much more building-specific data. ALL of the data input for a LEVEL TWO (Detailed) analysis involves making building-specific estimates which override the default values used in a LEVEL ONE (Minimum Data) analysis. For a LEVEL TWO (Detailed) analysis, there are five data tables where default information may be overridden by the user with building-specific information: 1. Building Depth-Damage Function 2. Contents Depth-Damage Function 3. Displacement Time 4. Functional Downtime 5. Mitigation Project Effectiveness This chapter reviews these five data tables and provides guidance about making building-specific estimates. I 8-1 VERSION 1.0 12/29194 LEVEL TWO: Buildina DDF VERSION 1.0 12/29/94 LEVEL TWO: Bulidina DDF I MI 9 IA M The Building Depth-Damage Function (DDF) indicates a building's vulnerability to flood damage by showing the expected levels of damage, both as a percentage of building replacement value and as dollars of damage for each flood depth. The Building Depth-Damage Function is the damage estimated to occur to a building at each flood depth. The following three sections, Reference Information from Level One Data, Building Depth-Damage Function, and Comments: Building DDF, all pertain to the Building Depth-Damage Function. The Building Depth-Damage Function section of the LEVEL TWO (Detailed) benefit-cost analysis is reached via the menu tree: Level Two Data I Building Depth-Damage Function 3 3 0jlqj Carry Over 4 Information ii'go. Sri;r g- PURPLE Blocks (Carry Over). Information from the LEVEL ONE Data page is displayed to identify the building under consideration and to provide reference information and guidance for the LEVEL TWO (Detailed) evaluation. 8-2 VERSION 1.0 12/29/94 1.0 12/29/94 LEVEL TWO: Buildina DDF VERSION LEVEL TWO: Building DDF~~~~~~~~~~~~ 0:1111193II3311 "", ITA" I0 0I E I Building, Depth-Damage . D EtiED Table fD ) DDFt0il There are five columns in the Building Depth-Damage Table. The first column shows the range of flood depths considered, from -2 to 18 feet. The next three columns contain damage estimates in percentages of the building's replacement value: Default DDF, User-Entered DDF, and Modified DDF (to account for the demolition damage threshold percentage). The fifth column converts the Modified DDF from percentages of damage into dollars of damage. Default ORANGE Blocks (Default). The Default Building DDF estimates Building DDF shown are based on the building type selected earlier and on Federal Insurance Administration (FIA) data.. FIA data on hundreds of thousands of flood damage claims are categorized into six classesof structures. These FIA data are predominantly, but not entirely, for residential buildings. In conformance with the FIA depth-damage data, the depth-damage table runs from -2 to 18 feet, with all depths relative to the Zero Flood Depth Elevation of the building (i.e., the top of the first finished floor). Damage data is included for depths below 0 feet because damage occurs at these flood levels for buildings with basements. The default depth-damage estimates have several limitations: 1. Only six classes of buildings are included. 2. No distinction is made between different types of construction. For example, one-story wood frame and masonry buildings are grouped in the same class. 3. No distinction is made for differences in construction practices or age of structures. I 8-3 VERSION 1.0 12/29/94 LEVEL TWO: Building DDF FIA Depth-Damage Table 4. FIA depth-damage estimates include all claims including flood damage due to high velocity flows, ice or debris flows, or erosion and soil/foundation failures. However, the preponderance of claims are due to water depth only and thus these depth-damage estimates approximate water depth only damages. 5. Damage estimates do not consider the flood duration. 6. Depth-damage data at high flood depths are based on many fewer claims than at lower flood depths and thus may be less reliable. For the above reasons, the Default DDF data should be regarded as a useful approximation to actual expected water depth-damages, but certainly not as absolute truth for all circumstances. The following table displays the default depth-damage estimates by flood depth for the six classes of building types plus the "other" classification included in the programs. These estimates are from the FIA flood damage claim data; values at a few depths have been interpolated between FIA data points. 8-4 VERSION 1.0 12/29/94 LEVEL TWO: Building DDF FIA DEPTH-DAMAGE DATA 1 Building I Story, 2 Story, Split I or 2 Split Mobile Other Type w/o W/o Level with Story, Level, Home Basement Basement Basement with with Flood Basement Basement D e p th _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -2 0 0 0 4 3 0 0 -1 0 0 0 8 5 0 0 0 9 5 3 11 6 8 0 1 14 9 9 15 16 44 0 2 22 13 13 20 19 63 0 3 27 18 25 23 22 73 0 4 29 20 27 28 27 78 0 5 30 22 28 33 32 80 0 6 40 24 33 38 35 81 0 7 43 26 34 44 36 82 0 8 44 29 41 49 44 82 0 9 45 33 43 51 48 82 0 10 46 38 45 53 50 82 0 11 47 38 46 55 52 82 0 12 48 38 47 57 54 82 0 13 49 38 47 59 56 82 0 14 50 38 47 60 58 82 0 15 50 38 47 60 58 82 0 16 50 38 47 60 58 82 0 17 50 38 47 60 58 82 0 18 50 38 47 60 58 82 0 8-5 VERSION 1.0 12/29/94 LEVEL TWO: Building DDF User-Entered BLUE Blocks (Override Default). If the Default DDF does not Building DDF accurately reflect the specific building under evaluation, users may enter more appropriate estimates based on engineering judgement and common sense. If the OTHER building type is selected, then no default values are provided and the user MUST enter building-specific estimates. Whenever a user enters a depth-damage estimate, the programs use these values rather than the default values, although the default values are displayed for comparison to the user-entered values. If building damage data at one observed flood depth are available, this value may be used to calibrate the user-entered building DDF. The percent damage at this flood depth can be set to agree with the actual damages, and damages at other flood depths can be smoothly adjusted to be consistent with the observed damage data point. However, it is important to note that the damages in a single flood may not or may not be representative of future expected damages, depending on whether or not unusual circumstances affected the observed damages. Overriding the default depth-damage estimates is perfectly acceptable, indeed it is required in order to get a valid benefit-cost analysis, whenever the default estimates do not accurately reflect the building under evaluation. For example, if a building is unusually resistant or unusually vulnerable to flood damage, this information should be reflected in the user-entered depth-damage function. Also, the default depth-damage estimates consider predominantly water depth. If high velocity flows, ice or debris-induced damage, erosion and soil/foundation failure, or unusually long-duration flooding are likely, then default depth-damage estimates MUST be adjusted accordingly. Modified Building DDF YELLOW Blocks (Results). The Modified DDF (%) takes into account the demolition threshold damage percentage entered on the LEVEL ONE Data page and adjusts the DDF accordingly. For example, if the demolition percentage is 40% then all damages at or above 40% are assumed to be 100%, because the building would be expected to be demolished as a total loss at that level of damage. YELLOW Blocks (Results). The depth-damage percentages of the Modified DDF (%) are converted to dollars in the final column of the depth-damage table. I 8-6 VERSION 1.0 12/29194 LEVEL TWO: Building DDF _ I I_ Comments PINK Block (Information Only). This comment box may be used to record specific information about the building which affects its vulnerability to.flood damage or any other information or assumptions which affect the user-entered depth-damage estimates (such as floods with debris or long duration flooding). Additionally, if OTHER was selected as the building type, a description of the building and its estimated depth-damage function should be entered here. 8-7 VERSION 1.0 12129/94 LEVEL TWO: Contents DDF VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF PCeel -TA The Contents Depth-Damage Function (DDF) indicates the building contents' vulnerability to flood damage by showing the expected levels of damage, both as a percentage of contents value and as dollars of damage for each flood depth. The following three sections, Reference Information from Level One Data, Contents Depth-Damage Function, and Comments: Contents DDF, all pertain to the Contents Depth-Damage Function, the damage estimated to occur to the building's contents at each flood depth. The Contents Depth-Damage Function section of the LEVEL TWO (Detailed) benefit-cost analysis is reached via the NEXT SCREEN button at the bottom of the Building Depth-Damage Function screen or the menu tree: Level Two Data I Contents Depth-Damage Function ~M WJI Carry Over InformationtV ntariti zrs b 777.7~j PURPLE Blocks (Carry Over). Information from the LEVEL ONE Data page is displayed to identify the building under consideration and to provide reference information and guidance for the LEVEL TWO (Detailed) evaluation. 8-8 VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF _ 3MIPMS I Contents Depth-Damage Table Default Contents DDF User-Entered Contents DDF There are five columns in the Contents Depth-Damage Table. The first column shows the range of flood depths considered, from -2 to 18 feet. The second carries over the Default or User-Entered Building DDF (if entered) from the Building Depth-Damage Function for reference. The next two columns contain estimated contents damage in percentages of the contents' value: Default DDF (%) and User- Entered DDF (%). The fifth column, DDF ($), converts the Default DDF (%)or, if entered, the User-Entered DDF (%) values into dollars. ORANGE Blocks (Default). The Default Contents DDF values shown are 150% of the default building damage percentages for the building type selected. The 150% multiplier assumes that typical contents are more vulnerable to flood damage than are typical buildings. The Default Contents DDF depends ONLY on the building type selected, NOT on the contents in any particular building. The vulnerability of contents to flood damage may vary markedly depending on the type of contents. For example, rare books are much more vulnerable than are used bricks. Therefore, users should enter building-specific estimates of the contents Default DDF whenever possible. BLUE Blocks (Override Default). If the Default DDF does not accurately reflect the Contents DDF of the specific building under evaluation, the user may enter more appropriate estimates based on engineering judgement, actual contents, and common sense. Also, if the OTHER building type is selected, then no default values are provided and the user must enter building-specific Contents DDF estimates. Whenever a user enters a depth-damage estimate, the programs use these values rather than the default values, although the default values are displayed for comparison to the user-entered values. 8-9 VERSION 1.0 12129/94 LEVEL TWO: Contents DDF VERSION 1.0 12/29/94 LEVEL TWO: Contents DDF Contents DDF ($) Comments: Contents DDF If contents damage data at one observed flood depth are available, then this value may be used to calibrate the user-entered Contents DDF. In this case, the percent damage at the observed flooddepth can be set to agree withthe observed damages, and damages at other flood depths can be smoothlyadjusted to be consistent withthe observed damage data point. However, it is important to note that the damages in a single flood may not or may not be representative of future expected damages, depending on whether or not unusual circumstances affected the observed damages. Overriding the default depth-damage estimates is perfectly acceptable, indeed it is required to get a valid benefit-cost analysis, whenever the default estimates do not accurately reflect the building under evaluation. For example, if a building's contents are unusually resistant or unusually vulnerable to flood damage, this information should be reflected in the user-entered Contents Depth-Damage Function. Also, the default depth-damage estimates consider predominantly water depth. If high velocity flows, ice or debris-induced damage, erosion and isoil/foundation failure, or unusually long-duration flooding are likely, then the default depth-damage estimates MUSTbe adjusted accordingly. YELLOWBlocks (Results). The contents depth-damage percentage estimates are converted to dollars in the final column of the Contents Depth-Damage Table. S40 II S SI PINK Block (Information Only) This comment box may be used to record specific information about the building contents which affects their vulnerability to flood damage or any other information or assumptions whichaffectthe user-entered contents depth-damage estimates (such as long duration flooding). 8-10 VERSION 1.0 12/29194 LEVEL TWO: Displacement Time Additionally, if OTHER was selected as the building type, a description of the building contents and their estimated depth-damage function should be entered here. As with the Building DDF, if OTHER is selected, no default values for the Contents DDF are provided. ff AAYMATORRDA0 AM 9 MA29174#10 The Displacement Time Estimates indicate the occupants' vulnerability to flood damage by showing the expected levels of displacement time, displacement costs, and rental income losses for each flood depth. Displacement Time is the number of days occupants must vacate the building because of flood damage. Displacement Time may be shorter than the repair time, because some flood damage repairs can be made with occupants in the building. The following three sections, Reference Information from Level One Data, Displacement Time Estimates, and Comments: Displacement Time Estimates, all pertain to the Displacement Time, the number of days of displacement estimated to occur to a building's occupants at each flood depth. The Displacement Time section of the LEVEL TWO (Detailed) benefit-cost analysis is reached via the NEXT SCREEN button at the bottom of the Contents Depth-Damage Function screen or the menu tree: Level Two Data I Displacement Time l I Carry.Over Information :t C o ua mj Gon;a PURPLE Blocks (Carry Over). Information from the LEVEL ONE Data page is displayed to identify the building under consideration and to provide reference information and guidance for the LEVEL TWO (Detailed) evaluation. 8-11 VFR92:ICnNI n 19190/QA LEVEL TWO: .Displacement Time VFD.IAM I fl 1919 QIQeI LEVEL TWO: Displacement Time lflwffmoail -| Displacement Time Estimate Table There are six columns in the Displacement Time Due to Building Flood Damage Table. The first column shows the range of flood depths considered, from -2 to 18 feet. The second column carries forward the Modified DDF (%) from the Building Depth-Damage Table for guidance. The third column, Default (days), shows the estimated number of days of displacement by flood depth. The fourth column, User-Entered (days), is for the user to override the default estimates by entering building-specific estimates. The fifth column calculates the Displacement Costs by flood depth from the Default or, if entered,the User-Entered Displacement Time Estimates (days) and the Total Displacement Costs($/day). The sixth column calculates the Rental Income Losses by flood depth from the Default or User-Entered Displacement Time Estimates and the Total Monthly Rent From All Tenants. Default ORANGEBlocks (Default). The Default Displacement Time Displacement Estimates (days) are derived from the Modified DDF (%) shown in the Time Estimates Building Depth-DamageTable. The Default estimates assumethat no displacement (i.e., renting of temporary space) occurs if the building sustains less than 10% damage. However, if the estimated building damage is greater than 10%, then the Default estimates of Displacement Time are scaled between 30 and 365 days. The 30 day minimum assumes that occupants won't relocate to temporary space if the damage is repairable within 30 days. The 365 day maximum assumes that all repairs will be completed and occupants will be back in the original space within one year. User-Entered BLUE Blocks (Override Default). If the Default Displacement Time Displacement Estimates do not accurately reflect the displacement times estimated Time Estimates for the occupants of the specific building under evaluation, users may enter more appropriate estimates based on engineering judgement, actual days of displacement observed, and common sense. 8-12 VERSION 1.0 12/29194 LEVEL TWO: Displacement Time Displacement Costs ($) Rental Income Losses Also, if the OTHER building type is selected, then no default values are provided and the user must enter building-specific estimates of the number of days of displacement. Whenever a user enters a Displacement Time Estimate, the programs use these values rather than the default values, although the default values are displayed for comparison to the user-entered values. If data on actual Displacement Time at one observed flood depth are available, then this information may be used to calibrate the user- entered Displacement Time Estimate. In this case, the Displacement Time at the observed flood depth can be set to agree with the observed displacement time; estimated displacement times at other flood depths can be smoothly adjusted to be consistent with the observed Displacement Time data point. However, it is important to note that the Displacement Time in a single flood may not or may not be representative of future expected times, depending on whether or not unusual circumstances affected the observed time. Overriding the Default Displacement Time Estimates is perfectly acceptable, indeed it is required to get a valid benefit-cost analysis whenever the default estimates do not accurately reflect the building under evaluation. For example, if local conditions suggest that unusually long or short displacement times are likely, this should be reflectedin the User-Entered Displacement Time Estimates. YELLOW Blocks (Results). The Default Displacement Time Estimates, or, if entered, the User-Entered Displacement Time Estimates are converted into Displacement Costs based on the Total Cost of Displacement per day (from the LEVEL ONE Data page) and the estimated days of displacement for each flood depth. YELLOW Blocks (Results). The Default Displacement Time Estimates, or, if entered, the User-Entered Displacement Time Estimates are converted into Rental Income-Losses based on the Total Monthly Rent from All Tenants ($/month, from the LEVEL ONE Data page) and the days of displacement for each flood depth. * 3 A A Comments PINK Block (Information Only). This comment box should be used to record specific information about the Displacement Time Estimates and how they are governed by the building's vulnerability to flood damage and any other information, assumptions or local conditinns. 8-13 VERSION 1.0 12129194 LEVEL TWO: Functional Downtime VERSION 1.0 12/29/94 LEVELTWO: Functional Downtime *DA A~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A Functional Downtime is the number of days a public/nonprofit agency cannot provide services due to disaster-caused damage. For example, an agency may have to relocate out of its building for 60 days, but may resume service provision from temporary quarters after only 7 days. Thus, in this case, the functional downtime due to disaster damage is 7 days. Functional Downtime is also used to estimate business income losses (if applicable) due to flood damage. The following three sections, Reference Information from Level One Data, Functional Downtime Estimates, and Comments: Functional Downtime Estimates, all pertain to the Functional Downtime Estimates, the days of lost function estimated to occur to at each flood depth. The Functional Downtime section of the LEVEL TWO (Detailed) benefit-cost analysis is reached via the NEXT SCREEN button at the bottom of the Displacement Time screen or the menu tree: Level Two Data I Functional Downtime 9MMMUlii CarryOver ~fo hsBidn tdy Information Ptat P a' 'ut ''- Etiae Nt ivco, o-Cdommercia A eBusine PURPLE Blocks (Carry Over). Information from the LEVEL ONE Data page is displayed to identify the building under consideration and to provide reference information and guidance for the LEVEL TWO (Detailed) evaluation. 8-14 VERSION 1.0 12/29/94 LEVEL TWO: Functional Downtime * A ** A Functional Downtime Table Default Functional Downtime Estimates User-Entered Functional Downtime Estimates There are six columns in the Functional Downtime Estimates table. The first column shows the range of flood depths considered, from -2 to 18 feet. The second column carries forward the Building DDF from the Building Depth-Damage table for guidance. The third column, Default Downtime, shows the estimated number of days of lost agency functioning by flood depth. The fourth column, User-Entered Downtime, is for the user to override the default estimates by entering building-specific estimates. The fifth column calculates the Value of Lost Services by flood depth from the Default or, if entered, the User- Entered Functional Downtime Estimates (days) and the Total Value of Lost Services ($/day). The sixth column calculates the Lost Business Income by flood depth from the Default or User-Entered Functional Downtime Estimates and the Estimated Net Income of Commercial Businesses ($/month). ORANGE Blocks (Default). The Default Downtime Estimates (days) are derived from the Building DDF (%) carried over from the Building Depth-Damage Function Table. The Default Downtime Estimates assume that if the building sustains less than 10% damage, then one day of Functional Downtime occurs for each 1% of damage. However, if the estimated building damage is greater than 10%, then the Default Downtime Estimates are scaled between 10 and 30 days. It is assumed that public/nonprofit agencies and businesses will resume function in temporary quarters, if necessary, within 30 days; thus the Default Functional Downtime Estimates are capped at 30 days. BLUE Blocks (Override Default). If the Default Functional Downtime Estimates do not accurately reflect the Functional Downtime estimated for the specific building under evaluation, users may enter more appropriate estimates based on engineering judgement, actual days of downtime experienced, and common sense. Also, if the OTHER building type is selected, then no default values are 8-15 VERSION 1.0 12/29194 LEVELTWO: Functional Downtime Value of Lost Services Lost Business Income Comments provided and the user must enter building-specific estimates of the number of days of functional downtime. Whenever a user enters a Functional Downtime Estimate, the programsuse these values rather than the default values, although the default values are displayed for comparison to the user-entered values. If data on actual Functional Downtime at one observed flood depth are available, then this information may be used to calibrate the user- entered Functional Downtime Estimate. In this case, the Functional Downtime at the observed flood depth can be set to agree with the observed time and estimated times at other flood depths can be smoothly adjusted to be consistent with the observed Functional Downtime data point. However, it is important to note that the Downtime in a single flood may not or may not be representative of future expected Downtimes, depending on whether or not unusual circumstances affected the observed Downtime. Overriding the default Functional Downtime estimates is perfectly acceptable, indeed it is required in order to get a valid benefit-cost analysis whenever the default estimates do not accurately reflect the building under evaluation. For example, if local conditions suggest that unusually long or short downtimes are likely, this information should be reflected in the user-entered Functional Downtime Estimates. YELLOW Blocks (Results). The Default Functional Downtime Estimates, or, if entered, the User-Entered Functional Downtime Estimates are converted into the Value of Lost Services based on the Total Value of Lost Services per day (from the LEVEL ONE Data page) and the estimated days of Functional Downtime for each flood depth. YELLOW Blocks (Results). Similarly,the Lost BusinessIncomefor each flood depth is based on the Estimated Net Income of Commercial Businesses ($/month) from the LEVEL ONE Data page, and the estimated days of Functional Downtime for each flood depth. _ 6 aO I PINK Blocks (Information Only). This comment box should be used to record specific information about the occupants' Functional Downtime as it is governed by the building's vulnerability to flood damage or any other information, local conditions, or assumptions which affect the user-entered Functional ilnwntime Estimates. 8-16 VERSION 1.0 12/29/94 LEVEL TWO: Mitigation Project Effectiveness M 7ZJA&MTi%# I #J'Ji--I FAIF422441 _JJ1J.t1AJ1#[ q A721111 Mitigation Effectiveness indicates the estimated percentage of damages and losses avoided by the mitigation measure for each flood depth. Mitigation Effectiveness estimates are made separately for avoiding building and contents damages. The following three sections, Reference Information from Level One Data, Mitigation Effectiveness, and Comments: Mitigation Effectiveness Estimates, all pertain to the Mitigation Project Effectiveness, the estimated percentage of damages avoided at each flood depth. The Mitigation Effectiveness section of the LEVEL TWO (Detailed) benefit-cost analysis is reached via the NEXT SCREEN button at the bottom of the Functional Downtime screen or the menu tree: Level Two Data I Mitigation Project Effectiveness. -. S £ Carry Over Information Tt Fr fi Tit, uIlrdingRp~cmotauX dIl PURPLE Blocks (Carry Over). Information from the LEVEL ONE Data page is displayed to identify the building under consideration and to provide reference information and guidance for the LEVEL TWO (Detailed) evaluation. 8-17 VERSION 1.0 12/29/94 LEVELTWO: Mitigation Project Effectiveness Mitigation Effectiveness Table Building Damages Default Effectiveness (%) AS -* 0. S S. .I. *S.S There are seven columns in the Mitigation Effectiveness Table. The first column shows the range of flood depths considered, from -2 to 1 8 feet. The second column shows Building Depth Damage Function Before Mitigation, for reference. The third column shows the Default Building Effectiveness Estimates. The fourth column is for the user to override the Default Building Effectiveness Estimates with User- Entered estimates. The fifth column shows the Contents Depth- Damage Function Before Mitigation, for reference. The sixth column shows the Default Contents Effectiveness Estimates. The seventh column is for the user to override the Default Content Effectiveness Estimates with User-Entered estimates. ORANGE Blocks (Default). The Building Damages Default Effectiveness (%) of the mitigation measure in avoiding building damages is calculated from the mitigation measure selected and the heights where the mitigation measure is 100% and 0% effective. These estimates of the Mitigation Project Effectiveness are entered in the Project Data section of the LEVEL ONE Data entry (see page 6-15). For relocation/buyout projects, the Default Mitigation Effectiveness of 100% for all flood depths is correct and need not be modified by user- entered input. Similarly, for elevation projects, the default values are generally applicable and probably should not have to be modified by user-entered input. 8-18 VERSION 1.0- 12/29/94 LEEL TOMiiainPoetEffectvns VERSION 1.0 12/29194 LEVEL TWO: Mitigation Proj.... Effectiveness Building Damages User-Entered Effectiveness (%) Contents Damages Default Effectiveness (%) Contents Damages User- Entered Effectiveness (%) For flood barrier projects, there may be more variation in effectiveness depending on the engineering details and thus the default values may or may not accurately reflect the effectiveness of all flood barrier projects. If the Other category is selected for mitigation measure then default estimates based on the heights of 100% and 0% effectiveness may also have to be modified. BLUE Blocks (Override Default). Users may override the Building Damages Default Effectiveness estimates by entering building- specific estimates in this column. Whenever a user enters a mitigation effectiveness estimate, the programs use these values rather than the default values, although the default values continue to be displayed for comparison to the user-entered values. If the Building Damages Default Effectiveness estimates do not accurately reflect the specifics of the building under evaluation, then enter more appropriate estimates based on engineering judgement and common sense. Overriding the Default Effectiveness Estimates is perfectly acceptable, indeed it is required in order to get a valid benefit- cost analysis, whenever the default estimates do not accurately reflect the building under evaluation. For example, if the particular mitigation measure under evaluation is expected to be unusually effective or unusually ineffective, this information should be reflected in the User- Entered Effectiveness Estimates. ORANGE Blocks (Default). The Contents Damages Default Effectiveness of the mitigation measure in avoiding contents damages is assumed to be the same as the Building Damages Default Effectiveness. See the Building Damages Default Effectiveness section above for a review of these assumptions. BLUE Blocks (Override Default) Users may override the Default Mitigation Effectiveness estimates by entering building-specific estimates in this column. Whenever a user enters effectiveness estimates, the programs use these values rather than the default values, although the default values continue to be displayed for comparison to the user-entered values. If the default mitigation effectiveness estimates do not accurately reflect the specific building under evaluation, then enter more appropriate estimates based on engineering judgement and common sense. Overriding Default Effectiveness Estimates is perfectly acceptable, indeed it is required to get a valid benefit-cost analysis whenever the default estimates do not accurately reflect the building under evaluation. For example, if the proposed mitigation measure is expected to be unusually effective or unusually ineffective, this information should be reflected in the user-entered Effectiveness Estimates. 8-19 VERSION 1.0 12/29/94 LEVEL TWO: Mitigation Project Effectiveness VERSION 1.0 12129/94 LEVEL TWO: Mitigation Project Effectiveness Other The effectiveness of the mitigation measure in reducing Displacement Effectiveness Time and Functional Downtime is assumed to be the same as the Assumptions effectiveness in avoiding building damages. 0U A& M3111 m E_ Comments PINK Blocks (Information Only). This comment box should be used to record specific information about the mitigation measure's effectiveness for both the building and content damages or any other information or assumptions which affect the User-Entered Mitigation Effectiveness Estimates. 8-20 VERSION 01.0 12/29/94 B-C PROGRAMS: Results CHAPTER 9 BENEFIT-COST PROGRAMS: RESULTS Introduction This chapter summarizes all of the results which are calculated from the data inputs. There are four main types of results: . Summary of Damages Before Mitigation, 2. Summary of Damages After Mitigation, 3. Benefit-Cost Results, and 4. Summary. Results should always be reviewed for reasonableness. If any of the results appear unreasonable, then check the corresponding input parametersl~~~Miiinwhich lead 1toDaathe results.a i~E TW11 | Each analyst conducting benefit-cost analysis has the responsibility to ensure that all data inputs are reasonable, defensible, and well- documented. The programs process all of the data inputs in a |mathematically correct manner, but the programs cannot produce correct results when incorrect data are entered. The analyst has control over the data inputs and thus responsibility for the results. I 9-1 VERSION 1.0 12/29/94 RESULTS: Damages Before Mitigation I A A: e This section of results characterizes the vulnerability of the EXISTING building to flood damages and losses BEFORE undertaking any mitigation measures. The estimated scenario damages and losses for the existing building at each flood depth depend directly on the depth- damage functions for building and contents, displacement, and functional downtimes, and all of the other data input parameters. The expected annual damages and losses also depend very strongly on the degree of flood risk at the site under evaluation. _WaBS_& ~p E~ X - A Scenario Damages Before Mitigation ($per event) Scenario Damages are defined as damages and losses per flood event (occurrence). Scenario damages indicate the estimated damages which would result from a single flood of a particular depth at the building under evaluation. For example, the scenario damages for a 3-foot flood are the expected damages and losses each time a 3-foot flood occurs at a particular site. Scenario damages do NOT depend on the probability of floods at that location. Scenario Damages Table The Scenario Damages Table contains scenario damages for each flood depth from -2 to 18 feet for six categories of damages and losses: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. In addition, the total damages and losses are shown for each flood depth. The information in this Scenario Damages Before Mitigation table shows the total vulnerability of the existing building to flood damage, how these damages are distributed among different categories of damages, and how these damages vary with flood depth. 9-2 VERSION 1.0,12129/94 RESULTS: Damages Before Mitigation I LINALi M IlJ, I I I LeY.A 3 E: ---am - - Expected Annual Damages Table Interpreting Damages Before Mitigation The Scenario Damages discussed above do NOT depend on flood hazard risk. Two identical buildings located at different elevations in a flood plain will have identical scenario damages at each flood depth. However, the probability of flood damage varies markedly with elevation in a flood plain. Expected Annual Damages take into account the annual probabilities of floods of each depth. Expected Annual Damages are the AVERAGE damages per year expected over a long time period. "Expected annual" does NOT mean that these damages will occur every year. For each flood depth, Expected Annual Damages are calculated by multiplying the Scenario Damages times the expected annual number (probability) of floods of each depth. The Expected Annual Damage Table contains expected annual damages for each flood depth from -2 to 18 feet for six categories of damages and losses: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. In addition, the total damages and losses are shown for each flood depth. Expected Annual Damages will generally be much smaller than Scenario Damages because the expected annual number or annual probability of a flood of a given depth is usually much less than one. Scenario Damages and Expected Annual Damages provide different information. Scenario Damages describe how much flood damage there will be each time a given flood occurs. However, because Scenario Damages DO NOT consider flood probabilities, they do not provide sufficient information for decisionmaking. Scenario Damages for a given flood depth may be high, but if the flood Probability is very 9-3 VERSION 1.0 12/29/94 ` Results: Damaaes After Mitioation VERSION 1.0 12/29/94 Results: Damaaes After Mitiantion low, no mitigation action may be warranted. For example, if a 5-foot flood causes $50,000 damages but such a flood is expected to occur only once in 1,000 years, then simply repairing the very infrequent flood damage may be the most sensible and cost-effective strategy. The Scenario Damages Before Mitigation and the Expected Annual Damages Before Mitigation provide, in combination, a complete picture of the vulnerability of the building to flood damage before undertaking a mitigation project. Expected Annual Damages DO consider flood probabilities. A building with high Expected Annual Damages means that not only are Scenario Damages high, but also that flood probabilities at the depths that cause considerable damages are relatively high. High Expected Annual Damages means that there are high potential benefits in avoiding such damages through mitigation projects. Even for buildings with high Expected Annual Damages, all mitigation projects are not necessarily cost-effective. Cost-effectiveness depends on the cost of the mitigation project and on the effectiveness of the mitigation project in avoiding damages, as well as on the Expected Annual Damages. A* *A ~rf ~A&Ala AA This section of results characterizes the vulnerability of the building to flood damages and losses AFTER undertaking a particular mitigation measure. Scenario damages after mitigation depend on the damages before mitigation and on the effectiveness of the mitigation measure in avoiding damages. The Expected Annual Damages and Losses after mitigation also depend very strongly on the degree of flood and flood-related risks at the site under evaluation. IMJH--61 eiSVI-11YA3I A A a -T1 111 &110 OEM=~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -~~~~ Scenario Damages After Mitigation are the damages and losses expected to occur per flood event after the mitigation project is implemented. For some mitigation projects, such as relocation or buyout, the Scenario Damages After Mitigation will be zero. For other projects, such as elevation or flood barriers, Scenario Damages After Mitigation will be lower than before mitigation but not zero at those Rood depths where the mitigation measure is partially effective. 9-4 VERSION 1.0 12/29/94 Results: DamagesAfter Mitigation Scenario Damages Table Scenario Damages After Mitigation indicate the estimated damages which would result from a single flood of a particular depth at the building under evaluation after completion of the mitigation project. For example, the scenario damages for a 3-foot flood are the expected damages and losses each time a 3-foot flood occurs at a particular site. Scenario damages DO NOT depend on the probability of floods at that location. The Scenario Damages After Mitigation Table contains scenario damages for each flood depth from -2 to 18 feet for six categories of avoided damages and losses: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. In addition, the total damages and losses are shown for each flood depth. The information in this Scenario Damages After Mitigation table shows the total vulnerability of the building after mitigation to flood damage, how these damages are distributed among different categories of damages, and how these damages vary with flood depth. In the example table above, Scenario Damages After Mitigation are zero for flood depths through 4 feet, because the mitigation measure (elevation) is 100% effective in avoiding damages at these flood depths. WC419 l3 lkl WA myA £lA 3 A I - Expected Annual Damages After Mitigation take into account the annual probabilities of floods of each depth. Expected Annual Damages are the AVERAGE damages per year expected over a long time period. "Expected annual" does not mean that these damages will occur every year. 9-5 VERSION 1.0 12/29194 Results: Damaaes After Mitiaation VERSION 1.0 12/29194 Results: DamaaesAfter Mitloation Expected Annual Damages After Mitigation also take into account the effectiveness of the mitigation measure at each flood depth. For some mitigation projects, such as relocation or buyout, the Expected Annual Damages After Mitigation will be zero. For other mitigation projects, such as elevation or flood barriers, Expected Annual Damages After Mitigation will be lower than before mitigation but not zero. For each flood depth, Expected Annual Damages After Mitigation are calculated by multiplying the Scenario Damages times the expected annual number (probability) of floods of each depth. The Expected Annual Damages After Mitigation table (shown above) contains expected annual damages AFTER mitigation for each flood depth from -2 to 18 feet for six categories of avoided damages and losses: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. In addition, the total damages and losses AFTER mitigation are shown for each flood depth. Interpreting The Scenario Damages After Mitigation and the Expected Annual Damages After Damages After Mitigation provide, in combination, a complete Mitigation picture of the vulnerability of the building to flood damages after undertaking a mitigation project. 9-6 VERSION 1.0 12/29/94 Results: Expected Annual Benefits U~~~~~~1 Expected Annual Benefits Table Benefits are damages and losses avoided because of the mitigation project. In other words, benefits are the difference in damages before and after the mitigation project. The Expected Annual Benefits of a mitigation project are the expected annual AVOIDED damages and losses. Thus, Expected Annual Benefits are the difference between Expected Annual Damages Before Mitigation and Expected Annual Damages After Mitigation. A I I i|iA_ FloogudC 0 t Daae aam C The final table in the Damages after Mitigation section shows the Expected Annual Benefits arising from the specific mitigation project under evaluation. The Expected Annual Benefits Table (shown above) contains expected annual benefits for each flood depth from -2 to 18 feet for six categories of avoided damages and losses: building damages avoided, contents damages avoided, displacement costs avoided, business income losses avoided, rental income losses avoided, and lost public/nonprofit services avoided. In addition, the total damages and losses avoided after mitigation are shown for each flood depth. The Total Expected Annual Benefits due to the mitigation project are the sum of the total avoided damages and losses over all of the flood depths. 9-7 VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results e -~~~~~~~- This section of results has three subsections: 1. Reference Information From LEVEL ONE Data, 2. Summary of Expected Annual Damages and Benefits, and 3. Summary of Project Benefits and Project Costs. U U Sm . 0 -, 0 Discount Rate The Discount Rate entry is determined by OMB/FEMA policy and cannot be varied by the user on a project-by-project basis. On October 29, 1992, OMB issued Circular A-94, Revised (Transmittal Memo No. 64), "Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs." Inthis Circular, OMB states that the appropriate discount rate varies depending on whether or not the investment (i.e., project) is an "internal Federal government investment." For FEMA-funded hazard mitigation projects for state and local governments (or eligible nonprofits)-,the OMB-mandateddiscount rate is the rate applicable for investments which are not internal Federal government investments. The OMB-mandateddiscount rate corresponds approximately to the 30-year Treasury bond rate, but the appropriate rate is specifically fixed by OMB annually. Currently, the OMB-mandated discount rate is 7% (see Appendix C of Circular A-94). For each disaster, an appropriate discount rate should be determined by FEMA, in accordance with the OMB guidance, and applied uniformly to all hazard mitigation projects being considered. The discount rate determined for each disaster is entered in the RED box under LEVEL ONE Data. After this rate is determined and entered ONCE, it can then be used for analysis of ALL hazard mitigation projects for this disaster. 9-8 -VERSION 1.0 12Z/29/94 RESULTS: Benefit-Cost Results Project Useful PURPLE Block (Carry Over). The Project Useful Life, entered on the Life LEVEL ONE (Minimum Data) screen, is carried over for reference. Present Value YELLOW Block (Result). The Present Value Coefficient is Coefficient mathematically determined by the discount rate and the project useful lifetime. The Present Value Coefficient is the present value of $1.00 per year in benefits received over the project useful lifetime. In other words, the Present Value Coefficient is a multiplier of the expected annual benefits which determines the net present value of the expected annual benefits. Calculated benefits and benefit-cost ratios are directly proportional to the Present Value Coefficient. However, in every case the discount rate and project useful lifetime entered by a user MUST be commensurate with the actual funding source for the project (see Discount Rate, pg. 9-8) and the actual mitigation project (see Project Useful Life, pg. 6-15). The following table shows the Present Value Coefficient for a wide range of discount rates and project useful lifetimes. an . ~~~ ~~~~~~ . I~~~~~~~~ . ~._ ---I. . D I .1 -i--.. < ,.x;ik9.s 9-9 VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results Summary of Expected Annual Damages and Benefits Table Expected Annual Damages and Losses Before Mitigation Expected Annual Damages and Losses After Mitigation Expected Annual Benefits 0 12 t 3 l l i l A YELLOW Blocks (Results). There are five columns in the Summary of Damages and Losses table. The first column contains the six types of damages and losses considered, along with a total. The second column is the Expected Annual Damages and Losses Before Mitigation. The third column is the Expected Annual Damages and Losses After Mitigation. The fourth column is the Expected Annual Benefits. The fifth column is the Present Value of Annual Benefits. The Expected Annual Damages and Losses Before Mitigation indicate the estimated average annual damages that are expected to occur before the mitigation project is completed. These figures indicate the vulnerability of the existing building to flood damages. See page 93 for more discussion. The Expected Annual Damages and Losses After Mitigation are the expected annual residual damages after completion of the mitigation project. In some cases, these damages and losses will be zero-(e.g., for buyout or relocation projects). See page 9-5 for more discussion. The Expected Annual Benefits of the mitigation project are the Expected Annual Avoided Damages. The Benefits of the mitigation project are exactly the amount of damages and losses which do not occur (i.e., are avoided) because of the mitigation measure. See page 9-6 for more discussion. 9-10 WERSION 1.0 12/29194 RESULTSI: Benefit-cost R esutst or ---w VERSION 10 12/29/94 RESULTS: Benefit-Cost Results Present Value of The Benefits are the present value (over the lifetime of the mitigation Benefits project under evaluation) of the Expected Annual Benefits or, equivalently, the present value of damages avoided. The last column of the Summary of Expected Annual Damages and Benefits table shows the Benefits (present value of damages avoided) for each of the six categories of damages and losses and in total. The final section of the Benefit-Cost Results page summarizes the results of the benefit-cost analysis. U A111-*nF1 Xft A il I Y9121a 1119* a Project Benefits and Project Costs k:4 PROJECT YELLOW Block (Result). The Project Benefits, whichwere BENEFITS calculated and displayed as the last entry in the bottom right corner of the Summary of Expected Annual Damages and Benefits Table, are presented again here. Project Benefits (i.e., the net present value of the Expected Annual Benefits over the lifetime of the project) are the productof the Present Value Coefficient andthe Expected Annual Benefits. PROJECT YELLOW Block (Result). The Project Costs are carried over from COSTS the LEVEL ONE Data entry page where they were entered for comparison to the calculated Project Benefits. BENEFITS YELLOW Block (Result). The difference between Project Benefits MINUS and Project Costs is displayed here in dollars. This value, also known COSTS as the present value criterion, shows the magnitude of the difference between Benefits and Costs. The present value criterion may be greater than zero (if benefits exceed costs) or less than zero (if costs exceed benefits). BENEFIT-COST YELLOW Block (Result). The Benefit-Cost Ratio is the Project RATIO Benefits divided by the Project Costs. For hazard mitigation projects under either Section 404 or Section 406, the Benefit-Cost Ratio MUST be equai to-or greater than one for funding eligibility. I 9-11 VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Resrnltsq VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results Interpreting Benefit-Cost Results Benefit-Cost Ratios, like all of the results of benefit-cost analysis, depend directly on the input data. Varying any of the input data which affect numerical results (i.e., changing any of the entries in green data entry blocks) will change the benefit-cost ratio. The sensitivity of calculated benefits and/or benefit-cost ratios to changes in the values entered in the model may be explored by varying input parameters one at a time (within credible or justifiable limits) and noting the impact on the resulting calculated benefits. Some of the input parameters have little impact on the benefit-cost ratio because they only govern a tiny portion of the benefits. Other input parameters have a major impact on benefit-cost results. The relative importance of each input parameter will vary from project to project depending on the specifics of each individual project. Because of the inherent uncertainties, benefit-cost results, like any calculation, should not be interpreted blindly or in disregard of the uncertainties. For example, three prospective flood hazard mitigation projects with benefit-cost ratios of 0.2, 1.2, and 2.2 are almost certainly distinguishable. Three prospective projects with benefit-cost ratios of 0.95, 1.00, and 1.05 are probably not significantly different. Three projects with ratios of 0.8, 1.0, and 1.2 may or may not be significantly different, depending on the validity of the input data. Benefit-cost ratios near one will always be in a gray area of interpretation. Depending on the accuracy of the input data, benefit- cost ratios near one (e.g., 0.9 or 1.1) may not be significantly different from 1. That is, with reasonable and defensible variations in estimates made in the input parameters, the benefit-cost results can come out either somewhat above or somewhat below one. The real power of benefit-cost analysis is to separate projects with benefit-cost ratios substantially below one from projects with benefit-cost ratios substantially above one. There will always be projects on the borderline, subject to results indicating benefit-cost ratios greater than or less than one, depending on variations in input data assumptions. In this context, the relative rankings of benefit-cost results may be more significant than the absolute benefit-cost ratios. Thus, if similar assumptions are made about roughly similar projects, the ranking of benefit-cost ratios accurately reflects relative differences between the projects, while the absolute numerical values of benefit-cost ratios reflect the general assumptions made in conducting the analyses. In comparing a range of projects with varying costs, benefits, and benefit-cost ratios, it is essential to consider the scale of the projects as well as the simple benefit-cost ratio. For example, a $5,000 project with a benefit-cost ratio of 2.0 (i.e., benefits of $10,000, present value criterion of $5,000) is not intrinsically a "better" project than a $500,00u 9-12 VERSION 1.0 VERSION 1.0 12/29/94 RESULTS: Benefit-Cost Results 12/29/94 RESULTS:Benefit-CostResults project with a benefit-cost ratio of 1.5 (i.e., benefits of $750,000 and a present value criterion of $250,000). Thus, in comparing projects it is necessary to consider both the benefit-cost ratios and the present value criterion (or the total amount of dollar benefits). Simple comparisons of projects using only the benefit-cost ratios are valid if and only if the projects are of closely similar size (cost). As discussed in Chapter 5, Benefit-Cost Model: Guidance, the accuracy, validity, and usefulness of any benefit-cost analysis depends on the correctness of the input data. A benefit-cost analysis in which ANY of the input data do not realistically reflect the particulars of the building and mitigation project under evaluation will be inaccurate and potentially misleading. As discussed in Chapter 5, many of the data inputs for benefit-cost analysis are not exact numbers, but rather informed estimates or judgements. Nevertheless, all of the data inputs as well as the results must be reviewed for reasonableness and defensibility. Benefit-cost analyses are subject to review and audit. Therefore, any analyses where the input parameters are not reasonable for the specific building and mitigation project under evaluation may be challenged. 9-13 VERSION 1.0 12/29/94 RFSULTS: siimmarv Single-Valued Data Entries Data that Vary by Flood Depth Summaryof Benefits and Costs The Summary page is in three parts: the first part contains all of the single-valued data entries, the second part contains a table of all data entries which vary by flood depth, and the third section contains a summary of the benefit-cost results. The three sections of the Summary Table are shown below: :wnmts CW 100 XSBE4V1 R 100R100 1 M3E4,f~9 '1l5174E028 100' 3S58AED0 A-100 1.t34E-03: 77' 4.45BE~-44 RRJb|EE1S v 26,17:6tI --~~~~tk, E#5097 PROJE4T,5!ENEFITSMINUS9WXM0 T$, E' E24.121) BENEFIT-COSTMRATIOV AmE.52~J' : 9-14 VERSION 1.0 12/29194 BENEFIT-COST PROGRAMS: Print-Out VERSION 1.0 12/29/94 BENEFIT-COST PROGRAMS: Print-Out CHAPTER 10 BENEFIT-COST PROGRAMS: PRINT-OUT I I The print-out which follows contains all data tables, results tables, and graphs from the Riverine Flood Benefit-Cost Program. The print-outconsists ofthree parts: 1. a one-page summary of data inputs; 2. a twelve-page report containing all of the data entry and results pages from the Benefit-Cost Program; and 3. seven pages of graphs illustrating flood hazard, damages, and benefit-cost results. The print-out from the Coastal A-Zone Benefit-Cost Program is virtually identical other than page three of the report which summarizes flood hazard data. The Riverine Flood data include frequency, discharge, and elevation data while the Coastal A-Zone Flood data include only frequency and elevation data. 10-1 RlverineFloodMitigatonProjecs V-i..~~~ -t-qAg laoi IR.e,1d1ericod Mltt.sU.nPtojeda V..,, 10Ia . IA 4O.A SUMMARY Scenario Run ID: L I City Office Annex 55 A Street Cape Squirrel, VA 22222 Mitigation Project: Elevate 5 feet Building Type: 2 Story wlo Basement DATA USED FOR THIS ANALYSIS: Building Replacement Value ($Isf) $75.00 Total Floor Area (square feet): 2,000 Total Building Replacement Value: $150,000 Demolition Threshold Damge Percentage: 50% Total Contents Value $50,000 Total Displacement Costs ($Imonth): $2,750 Cost of Providing Services from this Building ($Iday) $534 Post-Disaster Continuity Premium ($Iday) $500 Total Value of Lost Services (Sday) $1,034 Total Monthly Rent from All Tenants ($/month) $500 Estimated Net Income of Commercial Businesses ($lmonth) $1,500 Total Mitigation Project Costs $53,205 Discount Rate 7.00% Project Useful Life (years) 30 IDATA THAT VARY BY FLOOD DEPTH: Flood Building Modified Contents Displacement Functlonl| BuildingMIt. ContentsMii Annual# Depth(It) DDF DDF ( Time (days) Downtime(days) Effectiveness(%Effectiveness(OA of Floods -2 0 0 0 0 0 100 100 1.123E-01 -1 0 0 0 0 0 100 100 5.751E-02 0 5 5 8 0 5 100 100 6.450E-02 1 9 9 14 0 9 100 100 2.943E-02 2 13 13 20 54 13 100 100 1.208E-02 3 18 18 27 94 18 100 100 3.677E-03 4 20 20 30 110 20 100 100 1.221 E-03 5 22 22 33 126 22 77 77 4.494E-04 6 24 24 36 142 24 63 63 1.801E-04 7 26 26 39 158 26 50 50 7.752E-05 8 29 29 44 152 29 38 38 3.547E-05 9 33 33 50 214 30 39 39 1.711E-05 10 38 38 57 254 30 42 42 8.645E-06 11 38 38 57 254 30 37 37 4.548E-06 12 38 38 57 254 30 32 32 2.481E-06 13 38 38 57 254 30 24 24 1.397E-06 14 38 38 57 254 30 13 13 8.102E-07 15 38 38 57 254 30 0 0 4.822E-07 16 38 38 67 254 30 0 0 2.939E-07 17 38 38 57 254 30 0 0 1.831E-07 18 38 38 57 254 30 0 0 1.163E-07 SUMMARY OF PROJECT BENEFITS AND COSTS PROJECT BENEFITS $36,691 PROJECT COSTS $53,205 PROJECT BENEFITS MINUS PROJECT COSTS : ($16,513) BENEFIT-COST RATIO: 0.69 FEMADisclaimer:Theresults producedbythis analysisareneitherconclusiveevidencethat theproposedprojectIs cost-effective,nor a guaranteethat a prolectIs eligible for any governmentgrantforwhateverpurpose. AnMst Goatal&Homer 1212&'41,0h9:28:24, Gorttel&HomnerInc..2725 DoonerWay,Sacrneiant CA 93818,(i16)45i-4180 10-2 Rvm FIood mWSIen PMe VernWn 1.0, N.-It. 18. 1334 FEMA I Benefit-Cost Analysis of Hazard Mitigation Projects -ME RIVERINE FLOOD Version 1.0 November 18, 1994 Report of Benefit-Cost Analysis Building Name City Office Annex Address 65 A Street Cape Squirrel, VA 22222 Analyst Project Description Goettel & Horner Elevate 6 feet Project Number 123456 Application Date January 1, 1994 Scenario Run ID 1 Benefit-Cost Program Prepared for the FederalEmergency Management Agency by GOETTEL & HORNER INC. 2725 Donner Way Sacramento, Ca 95818 (916) 4514160 FAX (916) 451-3460 rEMA Dis;;Ialmer: The results produced by this analysis are neither conclusive evidence that the proposed project Is cost-effective, nor a guarantee that a project is eligible for any governmentgrant for whateverpurpose. 1212NS4. G."I uHo-lrln, CA M18, (018) 451-4160 0:25:34. & 2725 D-My, S 10-3 Rivenne Flood Mibgation Projects Verloin 1.0, Novembr 18, 1994 LEVELONE DATA Page .1I PROJECT INFORMATION Building Name City Office Annex Address 55 A Street City, State, Zip Cape Squirrel, VA 22222 Owner City of Cape Squirrel Contact Person Sam Smith, City Manager . . Disaster Number FE MA-000-D R-VA. Project Number N42 5 6 Application Date JanuFii 1, 11994 Discount Rate 7.00% Scenario Run ID I I Analyst JGoettel& Hor qr BUILDING DATA Building Type Selected | 2 Story wlo Basement BUILDING INFORMATION Zero Flood Depth (elevation in feet) Number of Stories Above Grade Construction Date Historic Building Controls BUILDING SIZE AND USE Total Floor Area (sf) rz2,000 Area Occupied by Owner or PubliclNonprofit Agencies (sf) 1 1500 . BUILDING VALUE Building Replacement Value ($Isf) $75.00 Total Building Replacement Value ($) $150,000 Building Damage that would Result in Demolition Percent Value 575,000 BUILDING CONTENTS Contents Description lofficefurniture, computers & files Total Value of Contents $50,000 Value of Contents ($lsf) 1 $25.00 DISPLACEMENT COSTS DUE TO FLOOD DAMAGE Rental Cost of Temporary Building Space ($1sflmonth) E 1.50 Rental Cost of Temporary Building Space ($/month) $2,250 Other Costs of Displacement ($/month) $500 Total Displacement Costs ($Imonth) $2,750 12128194,09:26:35, Goeltel & Homer Inc., 2725 Donner Way, Sacramento CA 95818, (916) 451-4160 10-4 Riverine Flood Mitigation Projects Version 1.0, November 18, 1994 LEVEL ONE DATA (Continued) Page 2 City Office Annex 55 A Street Cape Squirrel, VA 22222 Scenario Run ID 1 VALUE OF PUBLIC/NONPROFIT SERVICES Description of Services Provided City Planning Office Annual Budget of Public/Nonprofit Agencies $195,000 Is Rent Included in this Budget? | Rent Included If Rent is NOT Included, a Proxy Rent is Added to the Budget ($/month) l User-Entered Rent Estimate, in Place of Proxy Rent ($lmonth) $0 Cost of Providing Services from this Building ($/day) $534 Post-Disaster Continuity Premium ($/day) $500 Total Value of Lost Services ($/day) $1,034 RENT & BUSINESS INCOME Total Monthly Rent from All Tenants ($/month) $500 l Estimated Net Income of Commercial Businesses ($/month). $1,500 MITIGATION PROJECT DATA Type of Mitigation Selected Elevation Project Description [Elevate 5 feet I Project Useful Life (years) 30 Mitigation Effectiveness ,__ Mitigation Measure 100% Effective to Depth 0% Effective at Depth Elevation 4 NIA Relocation/Buyout NIA NIA Flood Barriers Other Mitigation Project Cost (excluding relocation costs) $40,000 Base Year of Costs 1994 Annual Maintenance Costs ($/year) $500 Present Value of Annual Maintenance Costs ($) $6,205 Relocation Costs for Mitigation Project Relocation Time Due to Project (months) 2 Rental Cost during Occupant Relocation ($Isflmonth) $2.00 Rental Cost during Occupant Relocation ($/month) $3,000 Other Relocation Costs ($/month) $500 Total Relocation Costs $7,000 Total Mitigation Project Costs $53,205 12128/94. 09:26:37. 10-5 Goettel& Homer Inc., 2725 Donner Way, Sacramento CA 95818, (916) 451-4160 RiverineFRod Midgaion PrcIects Version 10, November 1. 1¶994 IFLOODHAZARD RISK Page 3 City Office Annex 55 A Street Cape Squirrel, VA 22222 Scenario Run ID I 1 REFERENCE INFORMATION FROM LEVEL ONE DATA Zero Flood Depth (elevation in feet): I r,6 FLOOD HAZARD DATA Data from Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM) Flood Frequency Discharge Elevation (years) (cfs) (ft) 10 279,000 5.8 60 351,000 7.4 100 377,000 8.0 500 444,000 9.5 EXPECTED ANNUAL NUMBER OF FLOODS Flood Depth Default User (feet) Estimate Estimate -2 1.12E-01 -1 5.75E-02 0 6.45E-02 1 2.95E-02 2 1.21 E-02 3 3.68E-03 4 1.22E-03 5 4.49E-04 6 1.80E-04 7 7.75E-05 8 3.55E-05 9 1.71 E-05 10 8.64E-06 11 4.55E-06 12 2.48E-06 13 1.40E-06 14 8.10E-07 15 4.82E-07 16 2.94E-07 17 1.83E-07 18 1.16E-07 COMMENTS: FLOOD HAZARD RISK ESTIMATES 12123/94, 0:26:39, Gosptel&HomerInc., 2725 DonnerWay,SacramentoCA 95518, (916) 451-4160 10-6 RivenneFlood Mitigation Projects Verslon10, November 18 1994 LEVEL TWO DATA: BUILDING DEPTH-DAMAGE FUNCTION Page 4 | [City Office Annex 55 A Street Cape-Squirrel, VA 22222 a&w Scenario Run ID I I .1 REFERENCE INFORMATION FROM LEVEL ONE DATA Building Type: 1 2 Story wlo Basement ... Number of Stories Above Grade 2 Construction Date 1965 Historic Building Controls No Total Floor Area (square feet): 2,000 Total Building Replacement Value: $150,000 Demolition Threshold Damage Percentage: 50% BUILDING DEPTH-DAMAGE FUNCTION (DDF) ESTIMATED BUILDING DAMAGE Flood Depth Default User-Entered Modified Modified (feet) DDF (%) DDF (%) DDF (%) DDF ($) -2 °0 0 $0 -1 0 0 $0 0 5 5 $7,500 1 9 9 $13,500 2 13 13 $19,600 3 18 18 $27,000 4 20 20 $30,000 5 22 22 $33,000 6 24 24 $36,000 7 26 26 $39,000 8 29 29 $43,500 9 33 33 $49,500 10 38 38 $57,000 11 38 38 $57,000 12 38 38 $57,000 13 38 38 $57,000 14 38 38 $57,000 15 38 38 $57,000 16 38 38 $67,000 17 38 38 $57,000 18 38 . 38 $57,000 COMMENTS: BUILDING DDF 0926:411 2i28194, 10-7 Gottfl &Homer Inc., 2725 Donner Way. Samcmento CA 95818, (916) 451-4160 RN*ern Flood UW1gagon "acts Venlon 1.0, Nowrbor 18, IM1 RloeriM Flood lJfligation Prc.eCtI Varloo 1.0, November18.1004 I~LEVELTWO DATA: CONTENTS DEPTH-DAMAGE FUNCTION Page 5 I jCit OfficeAnnex 55 A Street Cape Squirrel,VA 22222 Scenario Run ID F I REFERENCE INFORMATION FROM LEVEL ONE DATA Contents Description Iofficefurniture, computers & files Total Value of Contents $ S50,000 Value of Contents ($Isf) F_ $25.00 CONTENTS DEPTH-DAMAGE FUNCTION (DDF) ESTIMATED CONTENTS DAMAGE Flood Depth Building Default User-Entered (feet) DDF(%) DDF (%) DDF (%) DDF ($) -2 0 0 $0 -1 0 0 $0 0 5 8 $3,750 1 9 14 $6,750 2 13 20 $9,750 3 18 27 $13,500 4 20 30 $15,000 5 22 33 $16,500 6 24 36 $18,000 7 26 39 $19,500 8 29 44 $21,750 9 33 60 $24,750 10 38 57 $28,500 11 38 57 $28,500 12 38 57 $28,500 13 38 57 $28,600 14 38 57 . $28,500 15 38 57 $28,500 16 38 57 $28,500 17 38 57 $28,500 18 38 57 . $28,600 COMMENTS: CONTENTS DDF 12128/94,09:28:43, Gouete & Homer Inc., 2725 DonnerWay. Sacramento CA 95818, (916) 451-4160 in-s Riveine Flood Miigaton Projects Version1.0. Novernber 18. 994 LEVEL TWO DATA: DISPLACEMENTTIME Page6 City Office Annex 55A Street Cape Squirrel, VA 22222 Scenario Run ID I 1 REFERENCE INFORMATION FROM LEVEL ONE DATA Rental Cost of Temporary Building Space($Isflmonth) Rental Cost of Temporary Building Space($/month) Other Costs of Displacement ($/month) Total Displacement Costs ($/month) Total Monthly Rent from All Tenants ($/month) I $500 DISPLACEMENT TIME DUE TO BUILDING FLOOD DAMAGE Flood Depth Modified Default User-Entered Displacement Rental Income (feet) DDF (%) (days) (days) Costs Losses -2 0 0 $0 $0 -1 0 0 $0 $0 0 5 0 $0 $0 1 9 0 $0 $0 2 13 54 _ $4,950 $900 3 18 94 $8,617 $1,567 4 20 110 $10,083 $1,833 5 22 126 . $11,550 $2,100 6 24 142 $13,017 $2,367 7 26 158 $14,483 $2,633 8 29 182 $16,683 $3,033 9 33 214 $19,617 $3,567 10 38 254 $23,283 $4,233 11 38 254 $23,283 $4,233 12 38 254 $23,283 $4,233 13 38 254 $23,283 $4,233 14 38 254 $23,283 $4,233 15 38 254 $23,283 $4,233 16 38 254 $23,283 $4,233 17 38 254 $23,283 $4,233 18 38 254 $23,283 $4,233 COMMENTS: DISPLACEMENT TIME ESTIMATES 1212894,09:25:45. 10-9 Goettel & Hornarlc 2725DonnerWay.Sarwnento CA95818.(916)451t41 Rtwfine Flood Mitlgaton Projeds V4ruon1.0, November 18, 1994 LEVEL TWO DATA: FUNCTIONAL DOWNTIME Page 7 CIty Office Annex 55 A Street Cape Squirrel, VA 22222 Scenario Run ID I 0 REFERENCE INFORMATION FROM LEVEL ONE DATA Cost of Providing Services from this Building ($/day) 5534 Post-DisasterContinuity Premium ($/day) $500 Total Value of Lost Services ($Iday) $1,034 Estimated Net Income of Commercial Businesses ($/month) $1,500 FUNCTIONAL DOWNTIME ESTIMATES Flood Depth Building Default User-Entered Value of Lost Business (feet | DDF (%) Downtime (days) Downtime (days) Lost Services Income -2 0 0 __ _ _ _ _ _ _$0 $07 -1 0 0 $0 $0 0 5 5 $6,171 $250 1 9 9 $9,308 $460 2 13 13 $13,445 $650 3 18 18 $18,616 $900 4 20 20 $20,685 $1,000 5 22 22 $22,763 $1,100 6 24 24 $24,822 $1,200 7 26 26 $26,890 $1,300 8 29 29 $29,993 $1,450 9 33 30 $31,027 $1,500 10 38 30 $31,027 $1,500 11 38 30 $31,027 $i,600 12 38 30 _ $31,027 $1,500 13 38 30 $31,027 $1,600 14 38 30 _ $31,027 $1,500 15 38 30 _ $31,027 $1,500 16 38 30 $31,027 $1,500 17 38 30 $31,027 $1,500 18 38 30 ._____ ._$31,027 $1,500 COMMENTS: FUNCTIONAL DOWNTIME ESTIMATES 12l28194.09:26:47. Goettal&Homer Inc.. 2725 DonnorWey. SacrawmntoCA 95818, (915) 4514160 10-10 RiverineFloodMitgationProjects Verslon1.0,November18,1994 [LEVEL TWO DATA TION PROJECT EFFECTIVENESS Page 8 I lCityOffice Annex 65A Street Cape Squirrel, VA 22222 Scenario Run ID I 1 | REFERENCE INFORMATION FROM LEVEL ONE DATA Building Type towoBasement Total Floor Area (sf) 2,000 Total Building Replacement Value Demolition Threshold Damage Percentage 50% Type of Mitigation Selected II Kiw;Elevation Project Description IElevate 5 feet Total Mitigation Project Costs I $53,205 MITIGATION EFFECTIVENESS (percent of damages avoided) BUILDING DAMAGES CONTENTS DAMAGES Flood Depth Building Default User-Entered Contents Default User-Entered (feet) DDF (%) Eff. (%) Eff.(%) DDF (%) Eff. (%) Eff. (%) -2 0 100 0 100 -1 0 100 0 100 0 5 100 8 100 1 9 100 14 100 2 13 100 20 100 3 18 100 27 100 4 20 100 30 100 5 22 77 33 77 6 24 63 36 63 7 26 50 39 50 8 29 38 44 38 9 33 39 50 39 10 38 42 57 42 11 38 37 57 37 12 38 32. 57 32 13 38 24 57 24 14 38 13 57 13 15 38 0 57 0 16 38 0 57 0 17 38 0 57 0 18 38 0 57 0 COMMENTS: MITIGATION EFFECTIVENESS ESTIMATES 12M2N. 09:26:50. 10-11 Goettel&Homerlnc.,2725DonnerWay.SacramentoCA95818.(916)4514180 thwine Flood M~artion Prmicts VasoIA .,N&MIM, SUMMARY OF DAMAGES BEFORE MITIGATION Page 9 City Office Annex 55 A Street Cape Squirrel, VA 22222 Scenario Run ID | Building Type 2 Story wlo Basement I SCENARIO DAMAGES BEFORE MITIGATION($ per event) Flood Building Contents Displacement Business Rental Pubilc/ Depth Damages Damages Costs Losses Losses Nonprofit Total -2 $0 $0 $0 $0 $0 $0 $0 -t $0 $0 SO SO $0 $0 $0 0 $7,500 $3,750 $0 $250 $0 $5,171 $16,671 1 $13,500 $6,750 $0 $450 $0 $9,308 $30,008 2 $19,500 $9,750 $4,950 $650 $900 $13,445 $49,195 3 $27,000 $13,500 $8,617 $900 $1,567 $18,616 $70,200 4 $30,000 $15,000 $10,083 $1,000 $1,833 $20,685 $78,602 5 $33,000 $16,500 $11,550 $1,100 $2,100 $22,753 $87,003 6 $36,000 $18,000 $13,017 $1,200 $2,367 $24,822 $95,405 7 $39,000 $19,500 $14,483 $1,300 $2,633 $26,890 $103,807 8 $43,500 $21,750 $16,683 $1,450 $3,033 $29,993 $116,410 9 $49,500 $24,750 $19,617 $1,500 $3,567 $31,027 $129,961 10 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 11 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 12 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 13 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 14 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 15 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 16 $57,000 $28,soo $23,283 $1,500 $4,233 $31,027 $145,544 17 $57,000 $28,600 $23,283 $1,500 $4,233 $31,027 $145,544 18 $57,000 $28,500 $23,283 $1,S00 $4,233 $31,027 $145,544 EXPECTED ANNUAL DAMAGES BEFORE MITIGATION($ per year) Flood Building Contents Displacement Business Rental Public] Depth Damages Damages Costs Losses Losses Nonprofit Total -2 SO $0 $0 $0 $0 $0 $0 -1 S0 $0 $0 $0 $0 $0 $0 0 $484 $242 $0 $16 $0 $334 $1,075 I $398 $199 $0 $13 $0 $274 $885 2 $236 $118 $60 $8 $11 $162 $594 3 $99 $50 $32 $3 $6 $68 $258 4 $37 $18 $12 $1 $2 $25 $96 s $15 $7 $5 $0 $1 $10 $39 6 $6 $3 $2 $0 $0 $4 $17 7 $3 $2 $1 $0 $0 $2 $8 8 $2 $1 $1 $0 $0 $1 $4 9 $1 S0 $0 $0 $O $1 $2 10 $0 $0 $0 $0 $0 $0 $1 11 $0 $0 $0 $0 $0 $0 $1 12 $0 $0 $0 $0 $0 $0 $0 13 $0 $0 $0 $0 S0 $0 $0 14 $0 $0 $0 $0 $0 $0 $0 1S $0 $0 S0 $0 $0 $0 $0 16 $0 $0 $0 $0 S0 $0 $0 17 sob $0 -__$0 _ __ $0 _ _ $0 18 $0 $0 $0 $0 $0 $0 $0 Total $1,281 $641 $114 $43 $21 $883 $2,982 12/2994,09:26:53. Goettel & Homer inc., 2725 Donner Way. Sacramento CA 95515, (916) 4514150 10-12 Riverne FloodMitigation Pmjects _in1 n w~h~ 1A -ul SUMMARY OF DAMAGES AFTER MITIGATION Page 10 | City Office Annex 55 A Street CapeSquirrel, VA 22222 Scenario Run ID Project Description |Elevate5 feet SCENARIO DAMAGES AFTER MITIGATION ($ per event) Flood Building Contents Displacement Business Rental Public/ Depth Damages Damages Costs Losses Losses Nonprofit Total -2 $0 $0 $0 $0 $0 $o so .1 $0 $0 $0 $0 $0 $0 $0 0 $0 $0 $0 $0 $0 $0 $0 1 $0 $0 $0 $0 $0 $0 So 2 $0 $0 $0 $0 $0 $0 $o 3 $0 $0 $0 $0 $0 $0 $0 4 $0 $0 $0 $0 $0 $0 $0 5 $7,500 $3,750 $2,625 $250 $477 $5,171 $19,774 6 $13,500 $6,750 $4,881 $450 $888 $9,308 $35,777 7 $19,500 $9,750 $7,242 $650 $1,317 $13,445 $51,904 8 $27,000 $13,500 $10,355 $900 $1,883 $18,616 $72,254 9 $30,000 $15,000 $11,889 $909 $2,162 $18,804 $78,764 10 $33,000 $16,500 $13,480 $868 $2,451 $17,963 $84,262 11 $36,000 $18,000 $14,705 $947 $2,674 $19,596 $91,923 12 $39,000 $19,500 $15,931 $1,026 $2,896 $21,229 $99,583 13 $43,500 $21,750 $17,769 $1,145 $3,231 $23,679 $111,073 14 $49,500 $24,750 $20,220 $1,303 $3,676 $26,945 $126,394 15 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 16 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 17 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 18 $57,000 $28,500 $23,283 $1,500 $4,233 $31,027 $145,544 EXPECTED ANNUAL DAMAGES AFTER MITIGATION ($ per year) Flood Building Contents Displacement Business Rental Publicl Depth Damages Damages Costs Losses Losses Nonprofit Total -2 $0 $0 $0 $0 $0 $0 $0 -1 $0 $0 $0 $0 $0 $0 $0 0 $0 $0 $0 $0 $0 $0 $0 I $0 $0 $0 $0 $0 $0 $0 2 $0 $0 $0 $0 $0 $0 $0 3 $0 $0 $0 $0 $0 $0 $0 4 $0 $0 $0 $0 $0 $0 $0 5 $3 $2 $1 $0 $0 $2 $9 6 $2 $1 $1 $0 $0 $2 $6 7 $2 $1 $1 $0 $0 $1 $4 8 $1 $0 $0 $0 $0 $1 $3 9 $1 $0 $0 $0 $0 $o $1 10 $0 $0 $0 $0 $0 $0 $1 11 $0 $0 $0 $0 $0 $0 $0 12 $0 $0 $0 $0 $0 $0 $0 13 $0 $0 $0 $0 $0 $0 $0 14 $0 $0 $0 $0 $o $0 $0 15 $0 $0 $0 $0 $0 $0 $0 16 $0 $0 $0 $0 S 0 $0 $0 17 $U $0 $0 $0 $0 $0 $0 18 $0 $0 $0 $0 $0 $0 $0 Toal $9 $5 $3 $0 $1 $6 $25 17nA/G u,;co;3 n, li:6ZEli4, U8:Z0:55, 10-13 Goettel& Homer Inc.,2725 Donner Way. Sacnamento CA 95318, (91e) *45141W0 Rfernra FloodmlffoaimnProlicts Venslon1.0,Novamber18, 1994 SUMMARY OFBENEFITS FROMMITIGATION Page 11 _ City Offlce Annex 55 A Street Cape Squirrel, VA 22222 Scenarlo Run ID 1 Project Description |Elevate6 feet EXPECTED ANNUAL BENEFITS FROM MITIGATION ($ per year) Flood Building Contents Displacement Business Rental Public/ Depth Damages Damages Costs Losses Losses Nonprofit Total -2 $0 $0 $0 $0 $0 $0 $0 -1 $0 $0 $0 $0 $0 $0 $0 0 $484 $242 $0 $16 $0 $334 $1,075 1 $398 $199 $0 $13 $0 $274 $885 2 $236 $118 $60 $8 $11 $162 $594 3 $99 $50 $32 $3 $6 $68 $258 4 $37 $18 $12 $1 $2 $25 $96 5 $11 $6 $4 $0 $1 $8 $30 6 $4 $2 $1 $0 $0 $3 $11 7 $2 $1 $1 $0 $0 $1 $4 8 $1 $0 $0 $0 $0 $0 $2 9 $0 $0 $0 $0 $0 $0 $1 10 $0 $0 $0 $0 $0 $0 $1 11 $0 $0 $0 $0 $0 $0 $0 12 $0 $0 $0 $0 $0 $0 $0 13 $0 $0 $0 $0 $0 $0 $0 14 $0 $0 $0 $0 $0 $0 $0 15 $0 $0 $0 $0 $0 $0 $0 16 $0 $0 $0 $0 $0 $0 $0 17 $0 $0 $0 $0 $0 $0 $0 18 $0 $0 $0 $0 $0 $0 $0 Total $1,272 $636 $110 $42 $20 $877 $2,957 Gottel & HovmerInc., 2725 DonnerWay, SacramentoCA 95818, (916) 4514180 1228094,10:05:08, 10-14 Riverinn Flood MitigationProjects Version1 0, November 18, 1994 BENEFIT-COST RESULTS Page 1 City Office Annex 55 A Street Cape Squirrel, VA 22222 Scenario RunIDID Building Type L 2 Story wlo Basement Project Description IElevate5 feet REFERENCE INFORMATION FROM LEVEL ONE DATA Discount Rate 7.00% I Project Useful Life (years) 30 Present Value Coefficient 12.41 SUMMARY OF EXPECTED DAMAGES AND BENEFITS Expected Annual Expected Annual Expected Annual Present Value of Damages Damages Benefits Annual Benefits Before Mitigation After Mitigation V Building Damages $1,281 $9 $1,272 $15,779 Contents Damages $641 $5 $636 $7,890 DisplacementCosts $114 $3 $110 $1,369 Business Income Lost $43 $0 $42 $526 Rental Income Lost $21 $1 $20 $249 Gov't Services Lost $883 $6 $877 $10,879 Total Losses $2,982 $25 $2,957 $36,691 A: PROJECT BENEFITS L_ ~$36,691 PROJECT COSTS I ~~$53,205 I BENEFITS MINUS COST S ($1 6,513) BENEFIT-COST RMIkTIO 1 0.69 L FEMADisclaimer: The results produced by this analysis are neitherconclusive evidencethat the proposedproject is cost-effective, nor a guaranteethat a project is eligible for any governmentgrant for whateverpurpose. 12f214,0C9:27:0J0, 10-15 Goettel&Homer Inc. 2725 DonnerWay, Sacramento CA95818,(916) 451-4160 Annual ExceedanceProbability vs. Flood Depth 0.3 U 0.25 ._ . … co-0.2 0 ._ L- a) 0.15 0 am 0.1 x 0) X w 0.05 0 Il I I I I oI***** -~A 6 I F l o o 1D 1e 1t 1 14 1h 16 17 18 Flood Depth Office Annex A.-City ExpectedAnnual Numberof Floods vs. Flood Depth 0.12 *0 to 0 0 0.1 -------------------------------------------0 0.08 .hm a) EC 0.06 b 0.04 ft) LU 0.02 A ~ ~ ~ ~ ~ ~ ~ ~ R 0 -2 -iI 6 2 1 a 6 6 1 9 . fofl f21Tf)3Q fS f6 fl Flood Depth -.-City OfficeAnn Scenario Damages Before Mitigation $160,000 $140,000 - Gov'tServices Lost $120,000RentalIncomeLost $100,000 --- ----------d Business IncomeLost $80,000 --------: ---4 1 N DisplacementCosts $60,000 -------------U Contents Damages $40,000 --------A Building Damages $20,000 - $0 - e1t 2 4 6 8D141l 1d 1 Flood Depth ExpectedAnnual Damages Before Mitigation $1,200 $1,000 ---- Gov't Services Lost Rental Income Lost z $600 -l--------BusinessIncomeLost U Displacement Costs U $200 -------- Contents Damages Building Damages $0 Flood Depth Scenario Damages After Mitigation $160,000 - $140,000- $120,000 -Gov'tServices Lost E $100,000 --- -------------------RentalIncomeLost $80,000-Business IncomeLost $60,000 -DisplacementCosts X $40,000-Contents Damages $20,000-BuildingDamages $0-I I I I I I 4 d6D t 1 14 16 18 Flood Depth ExpectedAnnual Damages AfterMitigation $10 $8-E Gov't ServicesLost _ $6-RentalIncome Lost Business IncomeLos E $4 0 DisplacementCostsContentsDamages $2 Building Damages ---1---------- $0 I I I I I I T -2 6 .4 1 F I b I I6 k 1 FloodDepth Expected Annual Benefits AnnualBenefits from Mitigation $1,200$ 1,000 - $800 -l $ t600 -------------------- $400° $ 2 00 -I ----I ------------ $0-L I l i 1-I L I I I I I Flood Depth MitigationProject Benefits Lost Services (29.65%) -BuildingDamages (43.00%) Rent Losses (0.68%o) BusinessLosses (1.43%o) DisplacementCosts (3.73%.Y) ContentsDamages(21.50%)-' VERSION 1.0 12/29/94 GLOSSARY Annual Budget of Public/ Nonprofit Agencies Avoided Damages and Losses Base Year of Costs Benefit-Cost Ratio Benefits Block Colors CHAPTER 11 GLOSSARY The annual budget of public/nonprofit agencies is the total annual operating budget of all the public/nonprofit agency functions located in a building, excluding "pass-through" monies (e.g., Social Security payments) which the agency receives and redistributes. The annual budget is used to value the loss of public/nonprofit services due to flood damages. Avoided damages and losses are the "benefits" counted in benefit-cost analysis. Six types of avoided damages and losses are counted in this benefit-cost program: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. The base year of costs is the year in which the mitigation project's costs were estimated and allows cost estimates made in prior years to be adjusted for any inflation in costs between the base year and the present time. The benefit-cost ratio is the ratio of the present value of benefits to project costs for the proposed mitigation project. The benefits counted in a benefit-cost analysis are the present value of the sum of the expected annual avoided damages over the lifetime of the mitigation project. Each block (cell) of data entry or data display areas of the program screens is color coded to inform the user what type of information each block contains. See Color Code chart, below. Also, see Style List. 11-1 VERSION 1.0 12/29/94 GLOSSARY Building Damages Building Depth- Damage Function (DDF) Building Replacement Value Building Reproduction Value Bu5lding-Specific Data Seven cell colors indicate different types of entries: GREEN Blocks (Data Input) require the user to enter data concerning the building or project and directly affect the calculated results. PINK Blocks (Information Only) contain information about the building or project and do not affect the calculated results. PURPLE Blocks (Carry Over) contain information that was entered by the user in other screens. ORANGE Blocks (Default) contain default data and cannot be changed. BLUE Blocks (Override Default) can be used to override default data with project-specific data. YELLOW Blocks (Results) contain calculated results from the model. RED Blocks (OMB Policy) contain entries that are defined by OMB or FEMA policy and thus are not user-defined entries. Building damages are the estimated damages to a structure, expressed as a percentage of the building's replacement value. Building damages include both structural and non-structural elements (mechanical, electrical, and plumbing systems) but exclude the building's contents. The building depth-damage function (DDF) indicates the building's vulnerability to flood damage by showing the estimated building damage for the range of flood depths from -2 to 18 feet above the top of the lowest finished floor. Building replacement value is the cost to provide a functionally- equivalent structure of the same size, generally of a more modern construction type. Replacement value does not include recreating historical or archaic materials, finishes or features. Building reproduction value is the cost of duplicating the design and architectural details of a specific, usual historic, building. Building-specific data are values which apply to the specific building under evaluation rather than to a generic building construction type. 11-2 VERSION 1.0 12/29/94 GLOSSARY, I Building Type Business Income Losses Buyout, Mitigation Measure Coastal Transect Construction Date Contents Damages Contents Depth- Damage Function Contents Value Building types considered in the model are the six Federal Insurance Administration (FIA) building types (1 story without basement, 2 story without basement, and split level without basement; 1 or 2 story with basement, split level with basement; and mobile home) plus an "other" category. The "other" category allows data inputs for building types not covered by the six FIA building types. Business income losses are the value of lost net business income due to flood damage. Buyout is a type of mitigation measure in which the owner's interest in the building is purchased and the building demolished. Buyouts are assumed to be 100% effective mitigation measures at all flood depths. Used in the Coastal-A Zone and Coastal-V Zone programs (but not in the Riverine Flood program), a coastal transect is a line drawn perpendicular to the coastline showing the A-Zone and V-Zone regions. Coastal transects are shown on maps in coastal Flood Information Studies. The construction date is the year during which the building's construction was started. Contents damages are the estimated damages to the building's contents, expressed as a percentage of the total contents' replacement value. Contents damages include furniture, office equipment, carpet, and other items specific to individual tenants' usages, but exclude mechanical, electrical, and plumbing systems which are non-structural parts of the building. The contents depth-damage function (DDF) indicates the content's vulnerability to flood damage by showing the estimated contents damage for the range of flood depths from -2 to 18 feet. The contents value is the estimated total value of the building's contents, including furniture, carpet, equipment, supplies, etc. I 11-3 VERSION 1.0 12/29/94 GLOSSARY Continuity Premium Cost of Occupant Displacement Default Building Depth-Damage Function Default Values Demolition Threshold Damage Percentage Depth-Damage Function (DDF) Discharge Discount Rate The post-disaster continuity premium is a means of more highly valuing public/nonprofit services which are particularly important in the post- disaster environment. The continuity premium is the extra dollar amount per day an agency would be willing to pay to maintain its functions after a flood. This premium is appropriate for those public/nonprofit services which may be more valuable than normal in the post-flood time period. The cost of occupant displacement is the total cost of displacement after a flood, including rent for temporary quarters, moving, and extra operating costs incurred because of displacement. The total cost of displacement of occupants is calculated from the displacement time and cost per month. The default building depth-damage function indicates a typical building's vulnerability to flood damage by showing the estimated levels of damage at each flood depth, based on the building type selected. Default, or reference, values are the estimated "typical" values contained in the program which are used in a LEVEL ONE (Minimum Data) analysis to facilitate a benefit-cost analysis for a "typical" building of the type selected. The demolition threshold damage percentage is the level of building damage, expressed as a percentage of the building's replacement value, at which the building is likely to be demolished rather than repaired. This percentage will vary depending on the type, style, age, condition, and historic significance of the structure. See Building Depth-Damage Function or Contents Depth-Damage Function. Discharge is the volume of water flow in a river or stream, usually measured in cubic feet per second. The discount rate is an interest rate which accounts for the time value of money. The discount rate is used to convert expected annual benefits over the lifetime of a project to a net present value. For Federally-funded hazard mitigation projects, the discount rate is determined by U.S. Office of Management and Budget (OMB) guidance. 11-4 VERSION 1.0 12/29/94 GLOSSARY VERSION 1.0 12129/94 GLOSSARY Displacement Costs Displacement costs are the product of displacement costs per month and the expected period for which the building will be unusable due to flood damage. Displacement costs are incurred when owners are displaced to a temporary site while flood-related damage to the original building is repaired and include costs for rent and other displacement expenses. Displacement Time Displacement time is the time during which an agency must operate from a temporary location due to flood-related damage while repairs are made to the original building. Compare with Functional Downtime. Economic Economic parameters used in the benefit-cost program are the Parameters Discount Rate, Project Useful Life, and Present Value Coefficient. Elevation, Elevation is a type of mitigation measure in which an existing building is Mitigation elevated to reduce future flood damages. Measure Estimated "Estimated" is used to denote data inputs which are based on judgement rather than exact values, and also to denote calculated results derived from other input parameters. In benefit-cost analysis "estimated" is distinct from "expected." See Expected. Exceedance The exceedance probability is the likelihood (probability) of exceeding a Probability particular value in a stated time period. For example, the annual exceedance probability for a 3-foot flood is the probability for all floods greater than or equal to a 3-foot flood. Expected "Expected" in benefit-cost analysis means a statistical, average value. For example, "expected" annual damages are the statistical average damages "expected" over a long time period. "Expected" annual damages do not occur every year. Expected Annual The expected annual avoided damages are the expected annual Avoided benefits counted in benefit-cost analysis. In other words, the expected Damages annual avoided damages are the difference between expected annual damages before and after mitigation. 11-5 VERSION 1.0 12/29/94 GLOSSARY VERSION 1.0 12/29194 GLOSSARY Expected Annual Expected annual damages before mitigation are the average damages Damages Before per year expected over a long time period. For each flood depth, Mitigation expected annual damages are calculated by multiplying the scenario damages before mitigation by the annual probability that a flood of each depth will occur. In this program, expected annual damages are calculated for six categories of damages and losses: building damages, contents damages, displacement costs, business income losses, rental income losses, and lost public/nonprofit services. Expected Annual Expected annual damages after mitigation are the average damages Damages After per year expected over a long time period. For each flood depth, Mitigation expected annual damages after mitigation are calculated by multiplying the scenario damages after mitigation times the annual probability that a flood of each depth will occur. Expected Annual The expected annual number of floods is the long term average annual Number of number of floods of a particular depth, from -2 to 18 feet. The expected Floods annual number of floods is closely similar to the annual probability of floods at each depth. Expected Net The expected net present value of a flood hazard mitigation project is Present Value the present value of benefits arising from the mitigation project. Expected annual benefits in each year of the useful lifetime of the project are discounted to present value and summed to obtain the net present value of benefits. Flood Barrier, A flood barrier is a type of mitigation measure in which barriers such as Mitigation flood walls, levees, or enclosures are constructed to prevent flood water Measure from reaching a structure. Flood Depth-The flood depth-damage table displays the estimated damage by flood Damage Table depth for the six classes of building types plus the "other" classification included in the program. Flood Risk The flood risk for a particular building is the expected annual number of floods, in one-foot increments from -2 to 18 feet in the program, at the building site. Flood risk varies markedly with elevation. See Zero Flood Depth Elevation. 11-6 VERSION 1.0 12/29/94 'GLOSSARY Freeboard Functional Downtime Income, Estimated Net Level One (Minimum Data) B-C Analysis Level Two (Detailed) B-CAnalysis Main Menu Menu Bar Menu Tree Freeboard is the additional height of a flood protection measure above an expected flood height which will provide an extra measure of flood protection. For example, to provide 1 00-year flood protection, levees normally are constructed with 3 feet above the 1 00-year flood elevation (i.e., with 3 feet of freeboard). Functional downtime is the time during which an agency/organization is unable to provide its services due to flood damage. Compare with Displacement Time. The estimated net income of commercial businesses is the net monthly income of commercial businesses in the building. A LEVEL ONE (Minimum Data) benefit-cost analysis uses "default" or reference data built into the program, and requires the minimum amount of building-specific and project-specific data. A LEVEL ONE analysis may be appropriate for small, low-cost projects or as an initial screening of larger projects. See LEVEL TWO (Detailed) benefit-cost analysis. A LEVEL TWO (Detailed) benefit-cost analysis is a highly detailed analysis in which default, or reference, values may be overridden with project-specific data. A LEVEL TWO analysis may be desirable for large, high-cost projects, projects which are politically sensitive, or projects where initial screening indicates that benefit-cost ratios are close to one, whenever the default values used in the LEVEL ONE (Minimum Data) analysis do not accurately reflect a specific project under evaluation, or where the results of a LEVEL ONE analysis indicate that a more detailed analysis is required to determine whether the project is cost-effective. The main menu is the list of headings which appears at the top of the display screen, customized for the benefit-cost program. The main menu headings in the Benefit-Cost Program are shown below: fEile Model tLevel OGneData7 Foodaard Risk HLevel Iwo ty The menu bar displays all the main menu headings of the benefit-cost program in the row near the top of the screen (i.e., word commands), under the words "Quattro Pro for Windows." The menu tree is the complete list of items which can be accessed by the menu bar. 11-7 VERSION 1.0 12/29/94 GLOSSARY Mitigation Measure Mitigation Project Cost Modified Building Depth- Damage Function Net Present Value (NPV) Other, Mitigation Measure Planning Horizon Post-Disaster Continuity Premium Present Value Present Value Coefficient A flood hazard mitigation measure is any project undertaken to mitigate the flood hazard. See Elevation, Flood Barrier, Relocation, and Buyout. The mitigation project cost is the sum of all direct construction costs plus other costs such as architectural and engineering fees, testing, permits, and project management but excludes relocation costs. See Relocation Costs. The modified building depth-damage function is the building DDF modified to account for the demolition threshold damage percentage. See Expected Net Present Value. The "Other" category of flood hazard mitigation projects includes wet floodproofing (see previous discussion on this subject) and any other measures not covered by the Elevation, Buyout, Relocation, or Flood Barriercategories. The planning horizon is the expected useful lifetime of the flood hazard mitigation project. See Project Useful Life. See ContinuityPremium. See Expected Net Present Value. The present value coefficient is a multiplier determined by the discount rate and the planning period which indicates the present value of $1.00 per year in benefits over the useful lifetime of the project. See Present Value. 11-8 VERSION 1.0 12/29/94 GLOSSARY Productivity The productivity tools SpeedBar is an additional row of symbols, usually Tools SpeedBar underneath the first SpeedBar, which provides access to more Quattro Pro features. Project Costs Project Useful Life Protected Blocks Public/ Nonprofit Services Lost Recurrence Intervals Relocation, Mitigation Measure Relocation Costs Rent, Total Monthly Project costs are the total mitigation project costs. See Mitigation Project Cost. The project's useful life is the estimated time period over which the mitigation project will maintain its effectiveness. Project useful life must be commensurate with the actual project being considered. Protected blocks cannot be changed by the user. Blocks colored orange, yellow, and purple are protected. Public/nonprofit services lost are those services which cannot be provided when a building becomes unusable during a flood. Avoided public/nonprofit services lost are one of the benefits counted in the benefit-cost program. A recurrence interval is the average time period between similar events (e.g., 100 years). A 1 00-year flood means a flood with a 1% annual probability of occurring. Relocation is a flood hazard mitigation alternative available in some situations. Relocation entails moving a structure out of the flood plain. Relocations are assumed to be 100% effective measures at all flood depths. Relocation costs are incurred when occupants must be relocated for construction of the mitigation project. In such cases, the Relocation Costs are an integral part of the mitigation project and must be counted in the total mitigation project costs. Total monthly rent is the amount of rent paid by all tenants in the structure. For a public/nonprofit building, the rent value entered should be only the rent for that portion, if any, rented to private tenants. 11-9 VERSION 1.0 12/29/94 GLOSSARY Rental Income Rental income losses are lost payments normally paid by private Losses tenants for all or a portion of the building. Inter-or intra-agency rents Scenario Damages Scenario Damages After Mitigation Scenario Damages Before Mitigation Scenario Run Identification SpeedBar Stories Above Grade .Style List within the Federal Government are not counted because such payments are generally transfers and their loss does not represent a true economic loss. Scenario damages are the damages per flood occurrence (i.e., event) of a given flood depth. In the program, scenario damages are expressed in 1-foot flood-depth increments from -2 to 18 feet. Scenario damages after mitigation are the estimated damages and losses from a single flood of a particular depth at the building after completion of the mitigation project. Scenario damages do NOT depend on the probability of floods at a location. Scenario damages are the damages and losses from a single flood of a particular depth at the building under evaluation before completion of the mitigation project. Scenario damages do NOT depend on the probability of floods at that location. The scenario run identification is a number or name which will distinguish this particular analysis from others. The SpeedBar is the row of icons (small pictures) just under the menu bar, i.e., the first row of buttons and tools. As the cursor moves across each item in the SpeedBar, an explanation of the button (or symbol) appears in the bottom left corner of the screen. Stories above grade are the number of stories above ground level in this building. The style list is the set of names which appear in the Style List window (located on the SpeedBar) which indicates the type of information contained in that block. The seven categories are the same as for the Block Colors. 11-10 VERSION 1.0 12/29/94 GLOSSARY Total Building Replacement Value Total Mitigation Project Costs Transect Zero Flood Depth Elevation Zoom List Box The total building replacement value is the product of the building replacement value per square foot and the building size Total mitigation project costs are the sum of the project costs and relocation costs necessary for the project. See Coastal Transect. The zero flood depth elevation of the building is the elevation of the top of the finished flooring of the lowest finished floor, as defined by the Federal Insurance Administration in compiling flood damage data. The zoom list box is the rectangular box in the third row at the top of the QPW window, which may be adjusted for the size of an individual computer screen display. 11-11 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS APPENDIXI ECONOMIC ASSUMPTIONS AND EQUATIONS I I The economic assumptions and equations which define the benefit-cost analysis of flood hazard mitigation projects are summarized in this appendix. Benefit-Cost Program The benefits of a flood hazard mitigation project are the avoided future damages and losses (i.e., the extent to which the mitigation project is effective in reducing expected future damages and losses). The net present value of benefits accounts for the time value of money, because benefits are expected to accrue in the future and dollars received in the future have a present value which is less than dollars received immediately. The expected net present value of a flood hazard mitigation project is the sum of the present value of net benefits expected to accrue each year over the life of the project, minus the initial cost of the mitigation project. The expected net present value, NPV, is defined as: NPV=-+ B B2 Bt BT INV 1+i (1+1)2 01+it (1+itr where: NPV is the expected net present value of a flood hazard mitigation project; B. is the expected annual net benefit of the hazard mitigation project for year t; i is the annual discount rate; T is the useful lifetime of the hazard mitigation project; and INV is the initial investment (the cost of the project). A-1 VERSION 1.0 VERSION 1.0 12129/94 ECNOI ASSUMPTIO' AND EUATIONS 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Each year's expected net benefit is discounted to its present value, then all years' expected net benefits are summed together to yield the total expected net present value. The planning horizon, or useful lifetime, of the hazard mitigation project varies depending on the type of project, with 30 to 50 years being common for building projects. The discount rate corrects benefits expected to be received in the future to their net present value. If expected net benefits are constant each year over the life of the project, the expected net present value equation is simplified to the constant annual benefits and one discount term representing the present value for the entire planning horizon. With this simplification, the expected net present value equation is reduced to: NPV = Bt t1-1+wT1_ INV For completeness, we mention two other factors which could be included in the expected net present value calculation: the salvage value of the mitigation investment at the end of the planning horizon and the annual costs to maintain the effectiveness of the mitigation project. However, the present value of the salvage value of flood hazard mitigation projects is generally quite small, because of the long planning horizons appropriate for building projects. Thus, salvage value is not considered in the program. The annual maintenance costs of typical Section 404 or 406 flood hazard mitigation projects are generally small, but may be significant, especially for levee projects. Therefore, for completeness, the annual maintenance costs are included in the benefit-cost program. The net present value of the annual maintenance costs is included in the total mitigation project costs. A-2 VERSIO1.0 1/29/94ECONOMIC VERSION 1.0 12/29/94 ASSUMPTIONS AND EQUATIONWS EconomicAssumptions for Modeling Benefits Underlying Assumptions The benefits of a flood hazard mitigation project are the reduction in damages that would otherwise be expected. Expected annual benefits are defined as the sum of expected avoided damages and losses. There are three different types of damages which are considered: scenario damages, expected annual damages, and expected annual avoided damages. Definitions of these terms are: Scenario Damages: the expected damages per flood of a given flood depth at the building, Expected Annual Damages: the product of scenario damages and the expected annual number of floods of a given flood depth at the building, and Expected Annual Avoided Damages (Expected Annual Benefits): the product of expected annual damages and the effectiveness of the mitigation measure in reducing damages at the building. A schematic example illustrating these damage terms is given below: Table 1 Flood Depth (ft) Scenario Damages Expected Annual Number of Floods Expected Annual Damages Effectiveness of Mitigation Measure Expectea Annual Benefits -2 $20,000 .10 $2000 100% $2,000 -1 $25,000 .05 $1250 80% $1,000 o $35,000 .02 $700 50% $350 1 $50,000 .01 $500 26% $125 2 $85,000 .005 $425. 15% $64 In this example, the scenario damages indicate the expected damages each time a flood of the given depth occurs at the building site. Scenario damages do not depend on how frequently such floods are expected to occur. The annual flood probabilities indicate the degree o- flood-related risk at the specific site under consideration. The expected annual damages are the product of scenario damages and annual flooa A-3 VERSION 1.0 12/29194 ECONOMIC ASSUMPTIONS AND EQUATIONS Benefits are AVOIDED Damages probability. Expected annual damages are the best estimate of the average damages per year expected at this site; such estimates do not indicate that these damages will occur every year. Expected annual damages are those damages which are expected to occur without undertaking the mitigation measure. The effectiveness of the mitigation measure is an estimate of how much expected damages will be reduced by the mitigation measure under consideration. The expected annual avoided damages (i.e., the annual benefits) are the product of expected annual damages and the effectiveness of the mitigation measure. The expected annual avoided damages are thus the expected annual benefits of undertaking the mitigation measure. A-4 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS VERSION hO 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Scenario Damages Building Damages Detailed Economic Assumpti-ons and--Equations Scenario damages (SCD) are the total damages per flood event. Thus, scenario damages are the sum of building damages (BD), contents damages (CD), displacement costs (DIS), lost business income (LBI), rental income losses (RENT), and the value of lost public/nonprofit services (VLS) per scenario (flood event). Scenario damages are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: SCD = BD + CD + DIS + LBI + RENT + VLS where: SCD is the total scenario (per event) damages; BD is the total building damage per scenario; CD is the total contents damage per scenario; DIS is the total displacement costs per scenario; LBI is the total lost business income per scenario; RENT is the total rental income losses per scenario; and VLS is the total value of lost public/nonprofit services per scenario. Building damages (BD) are estimated as the product of the modified depth damage function (MDDF), the floor area of the building (FA), and the replacement value of the building per square foot (BRV). Building damages are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: BD = (MDDF) (FA) (BRV) where: BD is the total amount of building damage per scenario; A-5 VERSION 1.0 12/29194 VERSION!1.0 12/29194 ECONOMIC ASSUMPTIONS AND EQUATIONSsECONMICASSUMPINS ANDEQUATINS MDDF is the modified depth damage function, the expected damage by flood depth expressed as a percentage of building replacement value; FA is the floor area of the building (in square feet); and BRV is the building replacement value (per square foot). Contents Contents damages (CD) are estimated as the product of the contents Damages depth-damage function (CDDF) and the total building contents replacement value (CRV). Contents damages are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: CD = (CDDF) (CR19 where: CD is the total contents damage; CDDF is the contents depth damage function, expressed as a percentage of contents replacement value for each flood depth; and CRV is the total building contents replacement value. Displacement Displacement costs (DIS) are the product of displacement days Costs necessary (DD), the displacement costs per square foot per day (DC), and the total area occupied by the owner agency or public or nonprofit agencies (TA). Displacement costs are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: DIS = (DD) (DC) (TA) where: DIS is the displacement costs per flood event; DD is the estimated number of displacement days necessary for each flood depth; DC is the displacement costs per square foot per day; and A-6 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Lost Business Income Rental Income Losses TA is the total area occupied by the owner agency or public/nonprofit agencies. Lost business income (LBI) is included if all or a portion of the building are rented to commercial businesses. Lost business income (LBI) is the product of the net income of commercial businesses per day (NICB) and the number of days of functional downtime (FDD). Lost business Income is calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: LBI = (NICB) (FDD) where: LBI is the total business income lost; NICB is the net income of commercial businesses per day; and FDD is the number of days of functional downtime. Rental income losses (RENT) are included if all or a portion of the building are rented to private tenants. Inter- or intra-agency rents within the federal, state, or local governments are not counted because such payments are generally transfers; loss of such payments does not represent a true economic loss. Other private sector economic losses (such as lost wages) are not considered because they are assumed to be generally negligible for public/nonprofit buildings. Rental income losses (RENT) are; the product of displacement days necessary (DD) and the daily rental rate (DRR). Rental income losses are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: RENT = (DD) (DRR) where: RENT is the total rental income lost; DD is the number of displacement days necessary; and DRR is the daily rental rate. A-7 VERSION 1.0 1 2129/94 ECNMCUASMTOSAN QAIN VERSION 1.O 12129/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Public/ For public/nonprofit sector buildings, the value of services lost (VLS) SNonprofit when the building becomes unusable during a flood must be included. Services Lost Expected Annual Damages Public/nonprofit services are valued using the Quasi-Willingness to Pay (QWTP) model. QWTP is a simple methodology that assumes that public/nonprofit services are worth what we pay to provide the services. VLS is the product of the total value of lost services per day (VOLS) and the number of days of functional downtime (FDD). The period of lost services depends on the agency's ability to find alternative quarters and to establish normal functions. This period may vary depending on the structure, size and function of the agency and the availability of suitable quarters after the flood. Note that the period of loss of agency function may be much shorter than the period of displacement necessary due to flood damage, because agencies will resume their functions in temporary quarters. The value of public/nonprofit services lost are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: VLS = (VOLS) (FDD) where: VLS is the value of lost agency services for a flood of a given depth; VOLS the total value of lost services per day; and FDD is the total number functional downtime days for a flood of a given depth. Expected annual damages (AD) are the product of scenario damages (SCD) and the expected annual number of floods of a given depth (EAE). Expected annual damages are calculated separately before and after the mitigation measure for each flood depth from -2 to 18 feet: AD = (SCD) (EAE) where: AD is the expected annual damages; SCD is the total scenario damages (as defined previously); and EAE is the expected annual number of floods of a given depth. A-8 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS ExpectedAnnual Benefits Expected annual benefits (EAB) are the product of expected annual damages (ADB) before mitigation and the effectiveness of the mitigation measure (EFF). Expected annual benefits are calculated for each flood depth from -2 to 18 feet: EAB = (AD B) (EFF) where: EAB is the expected annual benefits; ADW is the expected annual damages before mitigation; and EFF is the effectiveness of the mitigation measure in reducing expected damage from a flood of a given depth. Equivalently, expected annual benefits (EAB) are the difference between expected annual damages before mitigation (AD") and expected annual damages after mitigation (ADA). Expected annual benefits are calculated for each flood depth from -2 to 18 feet: EAB = AD" -AD A where: EAB is the expected annual benefits; ADW is the expected annual damages before mitigation; and ADA is the expected annual damages after mitigation. Total Expected Annual Benefits The total expected annual benefits (AB) of a flood hazard mitigation project are the expected annual benefits (EAB) summed over the full range of damaging floods considered (e.g., -2 feet to 18 feet). AB max = E EAB RF=mln where: AB is the total expected annual benefits of a flood hazard mitigation project; A-9 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS I RF min max EAB is the flood depth considered; is the minimum damaging flood considered (-2 feet in the Benefit-Cost Program); is the maximum flood considered (18 feet in the Benefit-Cost Program); and is the expected annual benefits from each flood depth being considered. Benefits The benefits (B) of a flood hazard mitigation project are the net present value of the total expected annual benefits (AB) over the useful lifetime of the hazard mitigation project (T) at an annual discount rate (I): B = AB 1i where: B AB T i is the benefits of a flood hazard mitigation project; is the expected annual benefits of the hazard mitigation project; is the useful lifetime of the hazard mitigation project; and is the annual discount rate. S Costs The total mitigation project costs (C) is the sum of the mitigation project costs (PC), the present value of the annual maintenance costs (PVAMC), and the relocation costs for the mitigation project (RC). C = PC + PVAMC + RC where: C PC is the total mitigation project costs; is the mitigation project costs including construction and other costs but excluding relocation costs; I PVAMC is the net present value of the annual maintenance costs of the mitigation project; and S A-10 VERSION 1.0 12129/94 ECONOMICARRI MPTIMIR AnKlCnl lA-rlnuk __VERSIOECONOMI ,N1.0 ./29/94 gUAI 2 I A-% %U RC is the relocation costs necessary for construction of the mitigation project. Benefit-Cost The benefit-cost ratio (BCR) is the benefits of the mitigation project (B), Ratio divided by the costs of the mitigation project (C). BCR = (B)I(C) where: BCR is the Benefit-Cost ratio of the hazard mitigation project; B is the benefits of the hazard mitigation project; and C is the total mitigation project costs. Present Value The present value criterion (PVC) is the benefits of the mitigationCriterion project (B), minus the costs of the mitigation project (C). PVC = B-C where: PVC is the present value criterion of the hazard mitigation project; B is the benefits of the hazard mitigation project; and C is the total mitigation project costs. I A-11 VERSION 1.0 VERSION 1.0 Benefit-Cost Analysis Cost-Benefit Analysis Cost- Effectiveness Analysis 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Technical Economic Terms Benefit-cost analysis provides estimates of the "benefits" and "costs" of a proposed project or change. The term "benefit-cost analysis" is used to denote economic analyses that apply either the maximum present value criterion or the benefit-cost ratio criterion to evaluate prospective actions. Both costs and benefits are discounted to their net present value. The maximum present value criterion subtracts costs from benefits to determine if benefits exceed costs. Benefit/cost ratios provide an alternative evaluation: prospective actions in which benefits exceed costs have benefit-cost ratios above one. The logic of benefit- cost analysis requires that benefit-cost ratios, and/or the present value criterion, be compared across competing alternatives. Cost-benefit analysis has identical economic assumptions to benefit- cost analysis and differs only in the nomenclature used to describe the analysis. Subtle differences in meaning between benefit-cost and cost- benefit analysis have been discussed (Hurter et al., 1982). These authors prefer the term benefit-cost for three reasons: 1 ) determining benefits is often the most difficult aspect of the analysis; if costs are placed first, the emphasis is wrong; 2) when ratios are used to compare projects, the ratio used is benefit-cost, not cost-benefit; and 3) placing the word "costs" first seems to suggest a negative attitude toward projects. It should be noted, however, that economic concepts, particularly as reflected in benefit-cost analysis, are completely neutral with respect to the undertaking of projects. Cost-effectiveness analysis identifies the least-cost way to achieve a stated objective; it is strictly a comparison among means to a given end (Andrews, 1982). Thus, cost effectiveness is the ability to achieve a given benefit at a minimum cost. In cost effectiveness analysis. the merits of the objective itself are not evaluated ineconomic terms. This approach is typically used to select methods of achieving specific environmental standards. The Stafford Act uses cost-effectiveness when it means that benefits exceed costs in §404, Hazard Mitigation, and §406, Public Assistance. A-12 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS Economic Efficiency Economic Impact Assessment Informal Benefit- Cost Analysis Risk-Benefit Analysis Economic efficiency is attained when the economy is functioning in a way that maximizes the value of society's consumption over time (Ward and Deren, 1991). Economic efficiency may also be viewed as the contribution to overall social welfare (Leman, 1989). It is generally accepted that a benefit-cost ratio above one indicates an improvement in economic efficiency. Benefit.cost analysis however does not indicate whether the project is the "most efficient" allocation of scarce resources for two reasons. First, benefit-cost analysis is an average rather than a marginal concept. The ratio indicates the relationship between benefits and costs for a given project size. Economic efficiency, however, requires that a project be sized where marginal benefits equal marginal costs, which maximizes the total net benefits. Second, the typical project benefit-cost analysis does not survey the complete array of spending alternatives for all public projects/programs unrelated to the project under analysis. Economic efficiency under a budget constraint would require that the marginal benefits for all public spending alternatives be equal. Economic impact assessment is both simpler and broader than either benefit-cost analysis or cost-effectiveness analysis in that it does not necessarily require aggregation or even categorization of effects as costs or benefits. It requires only the projection of economic effects of proposed actions and the listing of these for consideration. Impact assessment is broader than benefit-cost or cost-effectiveness analysis because it includes identification of all economic impacts: the changes in total (direct, indirect and induced) regional employment and income created by the proposed project. The inclusion of indirect and induced regional economic benefits and costs in the formal benefit-cost analysis is not generally accepted by the economics profession. Many economists maintain that such indirect and induced economic impacts represent a change in the distribution of economic activity and should not be confused with true gains in economic efficiency. Informal benefit-cost analysis embraces an indefinite range of procedures for the general identification and balancing of desirable and undesirable effects of proposed actions on society. Thus, informal benefit-cost analysis simply approximates pure common sense, and it should not be compared with formal economic analyses of prospective projects. Risk-benefit analysis compares the economic benefits of a proposed project with the environmental and/or health-safety risks that are also created by the project. Ideally, the environmental and/or health-safety risks should be quantified in economic terms which in many cases is almost, if not impossible. A-13 VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS VERSION 1.0 12/29/94 ECONOMIC ASSUMPTIONS AND EQUATIONS References Andrews, R.N.L. (1982) Benefit-Cost Analysis as Regulatory Reform, in Cost-Benefit Analysis and Environmental Regulations: Politics. Ethics and Methods, D. Swartzman, R.A. Liroff, and K.G. Croke (editors), The Conservation Foundation, Washington, D.C. Hurter, A.P. Jr., G.S. Tolley and R.G. Fabian (1982) Benefit-Cost Analysis and the Common Sense of Environmental Policy, in Cost-Benefit Analysis and Environmental Regulations: Politics. Ethics and Methods, D. Swartzman, R.A. Liroff, and K.G. Croke (editors), The Conservation Foundation, Washington, D.C. Leman, C.K. (1989) The Forgotten Fundamental: Successes and Excesses of Direct Government, in Beyond Privatization: The Tools of Government Action, L.M. Salamon (editor), The Urban Institute Press, Washington, D.C. Ward, W.A. and B.J. Deren (1991) The Economics of Project Analysis, A Practitioner's Guide. Economic Development Institute of the World Bank. A-14