Risk Management Series 
Design Guide for Improving School Safety in Earthquakes,  
Floods, and High Winds 
 
January 2004 

 
 
 
 
 
MAKING SCHOOLS SAFE AGAINST WINDS     6 
PART 2
 

6.10.5 Weatherstripping 
 
A variety of pre-manufactured weatherstripping components are available, 
including  
drips, door shoes and bottoms, thresholds, and jamb/head weatherstripping. A few  
examples of weatherstripping options are: 
¥ Drip. These are intended to shed water away from the opening between the frame  
and door head, and the opening between the door bottom and the threshold (see  
Figures 6-26 and 6-27). Alternatively, a door sweep can be specified (see Figure 
6- 
28); however, for high-traffic doors, periodic replacement of the neoprene will 
be  
necessary. 
 
¥ Door shoes and bottoms. These are intended to minimize the gap between the 
door  
and threshold. Figure 6-27 illustrates a door shoe that incorporates a drip. 
Figure  
6-29 illustrates an automatic door bottom. Door bottoms can be surface-mounted  
or mortised. For high-traffic doors, periodic replacement of the neoprene will 
be  
necessary. 
¥ Thresholds. These are available to suit a variety of conditions. Thresholds 
with  
vertical offsets offer enhanced resistance to wind-driven water infiltration.  
However, where Americans with Disabilities Act (ADA)-compliant thresholds are  
required, or at high-traffic doors, the offset is limited. However, at other 
doors,  
high offsets are preferred. 
 
 Thresholds can be interlocked with the door (see Figure 6-30) or thresholds can 
have  
a stop and seal (see Figure 6-31). In some instances, the threshold is set 
directly on  
the floor. Where this is appropriate, specify setting the threshold in butyl 
sealant  
to avoid water infiltration between the threshold and floor. In other instances, 
the  
threshold is set on a pan flashing as discussed in Section 6.10.4. If the 
threshold  
has weep holes, specify that the weep holes should not be obstructed (see Figure 
6- 
30). 
 
¥ Adjustable jamb/head weatherstripping. This type of jamb/head weatherstripping 
is  
recommended because these units have wide sponge neoprene that offers good  
contact with the door (see Figure 6-32). The adjustment feature also helps 
ensure  
good contact, provided the proper adjustment is maintained. 
¥ Meeting stile. At the meeting stile of pairs of doors, an overlapping astragal  
weatherstripping offers greater protection than weatherstripping that does not  
overlap. 
 
 
 
 
 
6.11 NON-LOAD BEARING WALLS, WALL COVERINGS, SOFFITS, AND  
UNDERSIDE OF ELEVATED FLOORS 
 
This section addresses exterior non-load bearing walls and provides guidance for  
interior non-load bearing masonry walls. Exterior wall coverings and soffits, as 
well as  
the underside of elevated floors, are also discussed. 
 
See Section 6.15.4 for schools located in hurricane-prone regions. 
 
 
 
6.11.1 Loads and Resistance 
 
The IBC requires that exterior non-load bearing walls, wall coverings, and 
soffits (see  
Figure 6-33) have sufficient strength to resist the positive and negative design 
wind  
pressure. Architects should specify that wall coverings and soffits comply with 
wind  
load testing in accordance with ASTM E 1233.   
 
Depending upon wind direction, soffits can experience either positive or 
negative  
pressure. Besides the cost of repairing damaged soffits, wind-borne soffit 
debris can  
cause property damage and injuries. 
 
Particular care should be given to the design and construction of exterior non-
load  
bearing walls constructed of masonry. Although these walls are not intended to 
carry  
gravity loads, they must be designed to resist the positive and negative wind 
loads in  
order to avoid collapse. Because of their great weight, when these types of 
walls  
collapse, they represent a severe risk to life as shown in Figure 6-14.  
Special consideration should also be given to interior non-load bearing masonry  
walls. Although these walls are not required by building codes to be designed to 
resist  
wind loads, if glazing is broken, the interior walls could be subjected to 
significant  
load as the school rapidly becomes fully pressurized. To avoid occupant injury 
(see  
Figure 6-34), it is recommended that interior non-load bearing masonry walls 
that are  
adjacent to student areas be designed to accommodate loads exerted by a design 
wind  
event, using the partially enclosed pressure coefficient. By doing so, wall 
collapse may  
be prevented if the building envelope is breached. This recommendation is  
applicable to schools in tornado-prone areas that do not have shelter space 
designed  
in accordance with FEMA 361, to schools located in areas with a basic wind speed  
greater than 120 mph, and to schools that will be used for hurricane shelters. 
 
 
6.11.2 Durability 
 
Where corrosion is problematic, stainless steel fasteners are recommended for 
wall  
and soffit systems. For other components (e.g., furring, blocking, struts, and  
hangars), the following are recommended: nonferrous components (such as wood),  
stainless steel, or steel with a minimum of G-90 hot-dipped galvanized coating. 
In  
addition, if air can freely circulate in a cavity (e.g., above a soffit), access 
panels are  
recommended so components within the cavity can be periodically observed for  
corrosion. 
 
 
6.11.3 Wall Coverings 
 
There are a variety of exterior wall covering options. Brick veneer, exterior 
insulation  
finish systems (EIFS), metal wall panels, and aluminum and vinyl siding have 
often  
exhibited poor wind performance. Veneers (such as ceramic tile and stucco) over  
concrete and cement-fiber panels and siding have also blown off. Blow-off of 
wood  
siding and panels is rare. 
Figure 6-35 shows brick veneer that was blown off. The bricks were attached to 
the  
back-up wall with corrugated metal ties. All of the following failure modes are  
commonly found in the vicinity of this type of common failure: 1)The nails pull 
out  
of the studs (smooth shank nails are typically used, hence they have limited  
withdrawal resistance; 2)The ties do not extend far enough into the mortar joint 
(i.e.,  
the tie is not long enough); 3)Although the ties make contact with the mortar, 
they  
are not well-bonded to it; 4)The ties are spaced too far apart; and 5)The ties 
provide  
essentially no resistance to compression. Hence, when a great amount of positive  
pressure is applied to the bricks, the brick joints flex. This flexing weakens 
the  
mortar joint. Walls that have not had bricks blown away have been found to be  
capable of being deflected with hand pressure. Although they look sound, in this  
condition they are very vulnerable to failure. Good reliable wind performance of 
brick  
veneer is very demanding on the designer and applicator. 
Figure 6-36 shows EIFS blow-off. In this case, the expanded polystyrene (EPS) 
was  
attached to gypsum board, which was attached to metal studs. The gypsum board  
detached from the studs, which is a common EIFS failure mode. When the gypsum  
board on the exterior side of the studs is blown away, it is common for gypsum 
board  
on the interior side to also be blown off. This then allows the school to become 
fully  
pressurized and allows entrance of wind-driven rain. Other common failure modes  
include separation of the EPS from its substrate and separation of the synthetic  
stucco from the EPS. Good reliable wind performance of EIFS is very demanding on  
the designer and applicator. Maintenance of EIFS and associated sealant joints 
is also  
demanding in order to minimize reduction of EIFS' wind resistance due to water  
infiltration. 
Another issue associated with EIFS is the potential for misdiagnosis of the wall  
system. EIFS is sometimes mistaken to be a concrete wall. If school personnel  
believed that an EIFS wall covering was a concrete wall and sought shelter from 
a  
tornado, instead of being protected by several inches of concrete, only two 
layers of  
gypsum board (i.e., one layer on each side of the studs) and a layer of EPS 
would be  
between the occupants and wind-borne debris. The debris could easily penetrate 
such  
a wall.  
 
EIFS can also be applied over concrete or CMU. In this scenario, the concrete or  
CMU could provide adequate missile protection provided it was thick enough and  
adequately reinforced. However, with this wall construction, there is still risk 
of blow- 
off of the EIFS. As discussed in Section 6.15.4, if the concrete or CMU is left 
exposed,  
there is no covering to be blown off. 
 
Wind performance of metal wall panels is highly variable. Performance depends  
upon strength of the specified panel (which is a function of material, panel 
profile,  
panel width and whether or not the panel is a composite) and the adequacy of the 
at- 
tachment (which can either be by concealed clips or exposed fasteners). A common  
problem is excessive spacing between clips/fasteners. Clip/fastener spacing 
should  
be specified, along with the specific type and size of fastener to be used.  
 
Figures 6-13  
and 6-43 illustrate metal wall panel problems. 
 
To minimize water infiltration at metal wall panel joints, it is recommended 
that  
sealant tape be specified at sidelaps when the basic wind speed is in excess of 
90 mph.  
However, end laps should be left unsealed so that moisture behind the panels can  
wick out. End laps should be a minimum of 3 inches (4 inches where the basic 
wind  
speed is greater than 120 mph) to avoid wind-driven rain infiltration. At the 
base of  
the wall, a 3-inch (4-inch) flashing should also be detailed, or the panels 
should be  
detailed to over-lap with the slab or other components by a minimum of 3 inches 
(4  
inches). 
Vinyl siding blow-off is typically caused by nails spaced too far apart and/or 
the use of  
vinyl siding that has inadequate wind-resistance. Vinyl siding is available with  
enhanced wind resistance features, such as an enhanced nailing hem, greater  
interlocking area, and greater thickness.  
Secondary Protection. Almost all wall coverings permit the passage of some water 
past  
the exterior surface of the covering, particularly when rain is wind-driven. 
Hence,  
most wall coverings should be considered as water-shedding, rather than as 
water- 
proofing coverings. To avoid moisture related problems, it is recommended that a  
secondary line of protection with a moisture barrier (such as housewrap or 
asphalt- 
saturated felt) and flashings around door and window openings be provided.  
Designers should specify that horizontal laps of the moisture barrier be 
installed so  
that water is allowed to drain from the wall (i.e., the top sheet should lap 
over the  
bottom sheet so that water running down the sheets remains on their outer 
surface).  
The bottom of the moisture barrier needs to be detailed to allow drainage. 
In areas that frequently experience strong winds, enhanced flashing details are  
recommended. Enhancements include use of flashings that have extra-long flanges,  
and use of sealant and tapes. Flashing design should recognize that wind-driven  
water can be pushed vertically. The height to which water can be pushed 
increases  
with wind speed. Water can also migrate vertically and horizontally by capillary 
action  
between layers of materials (e.g., between a flashing flange and housewrap). It 
is  
recommended that designers attempt to determine what type of flashing details 
have  
successfully been used in the area where the school will be constructed. 
If EIFS is specified, it is strongly recommended that it be designed with a 
drainage  
system that allows for dissipation of water leaks. 
 
 
6.11.4 Underside of Elevated Floors 
 
If sheathing is applied to the underside of joists or trusses elevated on piles 
(e.g., to  
protect insulation installed between the joists/trusses), its attachment should 
be  
specified in order to avoid blow-off. Stainless steel or hot-dip galvanized 
nails or  
screws are recommended. ASCE 7 does not provide guidance for load determination. 
 
 
 
 
  
6.12 ROOF SYSTEMS 
 
Because roof covering damage has historically been the most frequent and costly 
type  
of wind damage, special attention needs to be given to roof system design. 
Code Requirements. The IBC requires load resistance of the roof assembly to be  
evaluated by one of the test methods listed in IBC's Chapter 15. Architects are  
cautioned that designs that deviate from the tested assembly (either with 
material  
substitutions or change in thickness or arrangement) may adversely affect the 
wind  
performance of the assembly. The IBC does not specify a minimum safety factor.  
However, for the roof system, a safety factor of two is recommended. (To apply 
the  
safety factor, divide the test load by two to determine the allowable design 
load.  
Conversely, multiply the design load by two to determine the minimum required 
test  
resistance.) 
 
For metal panel systems, the IBC requires test methods UL 580 or ASTM E 1592. It 
is  
recommended that architects specify use of E 1592 because it is more likely to 
give a  
better representation of the system's uplift performance capability.  
Load Resistance. Specifying load resistance is commonly done by specifying a 
Factory  
Mutual Research (FMR) rating, such as Factory Mutual (FM) 1-75. The first number  
("1") indicates that the roof assembly passed the FMR tests for a Class 1 fire 
rating.  
The second number ("75") indicates the uplift resistance in psf that the 
assembly  
achieved during testing. Applying a safety factor of two to this example, this 
assembly  
would be suitable where the design uplift load is 37.5 psf.  
As previously discussed, because of building aerodynamics, the highest uplift 
load  
occurs at roof corners. The perimeter has a somewhat lower load; the field of 
the roof  
has the lowest load. FMG Data Sheets are formatted so that a roof assembly can 
be  
selected for the field of the roof. That assembly is then adjusted to meet the 
higher  
loads in the perimeter and corners by increasing the number of fasteners or  
decreasing the spacing of adhesive ribbons by a required amount; however, this  
assumes that the failure is the result of the pulling-out of the fastener from 
the deck,  
or that failure is in the vicinity of the fastener plate, which may not be the 
case. Also,  
the increased number of fasteners required by FM may not be sufficient to comply  
with the perimeter and corner loads derived from the building code. Therefore, 
if FM  
resistance data are specified, it is prudent for the architect to separately 
specify the  
resistance for the field of the roof (1-75 in the example above), the perimeter 
(1-130),  
and the corner (1-190).   
 
Edge Flashings and Copings. Roof membrane blow-off is almost always a result of  
lifting and peeling of the metal edge flashing or coping, which serves to clamp 
down  
the membrane at the roof edge (see Figure 6-37). Therefore, it is important for 
the  
architect to carefully consider the design of metal edge flashings, copings, and 
the  
nailers to which they are attached. ANSI/SPRI ES-1, Wind Design Standard for 
Edge Systems  
Used in Low Slope Roofing Systems provides general design guidance, including a  
methodology for determining the outward-acting load on the vertical flange of 
the  
flashing/coping (ASCE 7 does not provide this guidance). A minimum safety factor  
of three for edge flashings, copings, and nailers is recommended for schools.  
ANSI/SPRI ES-1 also includes test methods for assessing flashing/coping 
resistance.  
For FMG-insured schools, FMR approved flashing should be used and Data Sheet 1-
49  
should also be consulted.  
The traditional edge flashing/coping attachment method relies on concealed 
cleats  
that can deform under wind load and lead to disengagement of the flashing/coping  
(see Figure 6-38) and subsequent lifting and peeling of the roof membrane (as 
shown  
in Figure 6-11). When a vertical flange disengages and lifts up (as shown in 
Figure 6- 
38), the edge flashing and membrane are very susceptible to failure. Normally, 
when a  
flange lifts such as shown in Figure 6-38, the failure continues to propagate 
and the  
metal edge flashing and roof membrane blow off.  
 
Storm-damage research has revealed that, in lieu of cleat attachment, use of 
exposed  
fasteners to attach the vertical flanges of copings and edge flashings has been 
found  
to be a very effective and reliable attachment method (see Figure 6-39).  
If cleats are used for attachment, it is recommended that a bar be placed over 
the roof  
membrane near the edge flashing/coping as illustrated in Figure 6-40. The 
purpose  
of the bar is to provide secondary protection against membrane lifting and 
peeling in  
the event that the edge flashing/coping fails. A robust bar specifically made 
for bar- 
over mechanically attached single-ply systems is recommended. The bar needs to 
be  
very well anchored to the parapet or deck. Depending upon design wind loads, a  
spacing between 4 and 12 inches on center is recommended. A gap of a few inches  
should be left between each bar to allow for water flow across the membrane. 
After  
the bar is attached, it is stripped over with a stripping ply. 
Gutters. Special design attention needs to be given to uplift attachment of 
gutters,  
particularly those in excess of 6 inches wide.  Recommendations are provided in  
"Honing in on hangars," Professional Roofing, Thomas L. Smith, October 2002, pp. 
32  
(available on-line at www.nrca.net). 
 
Roof System Performance. Storm-damage research has shown that sprayed  
polyurethane foam and liquid-applied roof systems are very reliable high-wind  
performers. If the substrate to which the foam or liquid-applied membrane was  
applied does not lift, it is highly unlikely that the sprayed polyurethane foam 
(SPF) or  
the liquid-applied membrane will blow-off. Both systems are also more tolerant 
of  
missiles than other systems. Built-up roofs (BURs) and modified bitumen systems  
have also demonstrated good wind performance provided the edge flashing/coping  
does not fail (edge flashing/coping failure is common). The exception is 
aggregate  
surfacing, which is prone to blow-off (see Figure 6-11). Modified bitumen 
adhered to  
a concrete deck has demonstrated excellent resistance to progressive peeling 
after  
blow-off of the metal edge flashing. Metal panel performance is highly variable. 
Some  
systems are very wind-resistant, while others are quite vulnerable.  
Of the single-ply attachment methods, the paver-ballasted and fully adhered 
methods  
are the least problematic. Systems with aggregate ballast are prone to blow-off, 
unless  
care is taken in the design of the size of aggregate and the parapet height (see 
Figure  
6-8). Performance of protected membrane roofs (PMRs) with factory-applied  
cementitious coating over insulation boards is highly variable. When these 
boards  
are installed over a loose-laid membrane, it is critical that an air retarder be  
incorporated to prevent the membrane from ballooning and disengaging the boards.  
ANSI/SPRI RP-4 (which is referenced in the IBC) provides wind guidance for  
ballasted systems using aggregate, pavers, and cementitious-coated boards.  
The National Research Council of Canada, Institute for Research in 
Construction's  
Wind Design Guide for Mechanically Attached Flexible Membrane Roofs, B1049 
(2004) provides  
recommendations related to mechanically attached single-ply and modified  
bituminous systems. B1049 is a very comprehensive wind design guide and includes  
discussion of air retarders, which can be effective in reducing membrane 
flutter, in  
addition to their beneficial use in ballasted single-ply systems. When a 
mechanically  
attached system is specified, careful coordination with the structural engineer 
with  
respect to selection of deck type and thickness is important. If a steel deck is  
specified, it is critical to specify that the membrane fastener rows run 
perpendicular  
to the steel flanges in order to avoid overstressing attachment of the deck to 
the deck  
support structure (see Figures 6-41 and 6-42). In Figure 6-42, the flange with  
membrane fasteners carries essentially all of the uplift load because of the 
deck's  
inability to transfer any significant load to adjacent flanges. Hence, at the 
joists, the  
deck fasteners on either side of the flange with the membrane fasteners are the 
only  
connections to the joists that are carrying uplift load. Had the membrane 
fasteners  
shown in Figure 6-42 been run perpendicular to the deck flanges, each of the  
fasteners connecting the deck to the joists would have been carrying uplift 
load.  
Recommendations related to metal panels is provided in "Insights on Metal Roof  
Performance in High-wind Regions," Professional Roofing, Thomas L. Smith, 
February  
1995, pp. 12 (available on-line at  www.nrca.net). 
 
Parapet Base Flashings. Loads on parapet base flashings were first introduced in 
the  
2002 edition of ASCE 7. The loads on base flashings are greater than the loads 
on the  
roof covering if the parapet's exterior side is air-permeable. When base 
flashing is  
fully adhered, it has sufficient wind resistance in most cases. However, when 
base  
flashing is mechanically fastened, typical fastening patterns may be inadequate,  
depending upon design wind conditions (see Figure 6-43). Therefore, it is 
imperative  
that base flashing loads be calculated and attachments be designed to 
accommodate  
the loads. It is also important for designers to recognize and specify different  
attachment spacings in parapet corner regions versus regions between corners.  
Further discussion is provided in "Detailing ASCE 7's changes," Professional 
Roofing,  
Thomas L.  Smith, July 2003, pp. 26 (available on-line at www.nrca.net). 
 
Lightning Protection Systems. When not adequately integrated into a roof system, 
a  
lightning protection system can become detached from the roof during high winds.  
The detached system can damage the roof covering (see Figure 6-44). In addition, 
a  
detached system is no longer capable of providing lightning protection. Most  
manufacturers of lightning protection systems and most roofing manufacturers  
provide vague or inadequate details for securing a lightning protection system 
to a  
roof.   
 
During prolonged high winds, repeated slashing of the membrane by loose  
conductors ("cables") and puncturing by air terminals can result in lifting and  
peeling of the membrane. It is, therefore, important to adequately design the  
attachment of the lightning protection system. Recommendations pertaining to  
wind-resistant design, and specification and installation of lightning 
protection  
systems are provided in  "Integrating a Lightning Protection System in a Roof  
System," Thomas L. Smith, 12th International Roofing and Waterproofing  
Conference Proceedings (CD), National Roofing Contractors Association, 2002. 
Hurricane-prone Regions. See Section 6.15.5 for schools in hurricane-prone 
regions. 
 
Tornado-prone Regions. In order to reduce the number of wind-borne missiles, it 
is  
recommended that aggregate surfacings, pavers, tile, and slate not be specified 
on  
schools in tornado-prone regions (as defined in Section 6.7.1; see Figure 6-8). 
 
 
 
 
 
6.13 WINDOWS AND SKYLIGHTS 
 
This section addresses exterior windows and skylights. See Section 6.15.6 for 
schools  
located in hurricane-prone regions 
 
6.13.1 Loads and Resistance 
 
The IBC requires the window, curtain wall, or skylight assembly (i.e., the 
glazing,  
frame, and frame attachment to the wall or roof) to have sufficient strength to 
resist  
the positive and negative design wind pressure (see Figure 6-45). Architects 
should  
specify that these assemblies comply with wind load testing in accordance with 
ASTM  
E 1233. It is important to specify an adequate load path and to check its 
continuity  
during submittal review. 
 
In tornado-prone regions, some school districts may desire to have laminated 
glazing  
installed at exterior openings in order to provide wind-borne debris protection  
during weak tornadoes. Laminated glazing may also offer protection during strong  
tornadoes, but should not be relied upon for violent tornadoes. Further 
discussion is  
provided in Section 6.15.6. 
 
6.13.2 Durability 
 
Where corrosion is problematic, anodized aluminum or stainless steel frames and  
stainless steel frame anchors are recommended. 
6.13.3Water Infiltration 
When heavy rain accompanies high winds (e.g., thunderstorms, tropical storms, 
and  
hurricanes), it can cause wind-driven water infiltration problems; the magnitude 
of  
the problem increases with the wind speed. Leakage can occur at the 
glazing/frame  
interface, at the frame itself, or between the frame and wall. When the basic 
wind  
speed is greater than 120 mph, because of the very high design wind pressures 
and  
numerous opportunities for leakage path development, some leakage should be  
anticipated when design wind speed conditions are approached.   
The challenge with windows and curtain walls is successful integration between 
these  
elements and the walls. To the extent possible, detailing of the interface 
between the  
wall and the window or curtain wall units should rely on sealants as the 
secondary  
line of defense against water infiltration, rather than making the sealant the 
primary  
protection.   
 
When designing joints between walls and windows and curtain wall units, consider  
the shape of the sealant joint (i.e., a square joint is typically preferred) and 
the type of  
sealant to be specified. The sealant joint should be detailed so the sealant is 
able to  
bond on only two opposing surfaces (i.e., a backer rod or bond-breaker tape 
should  
be specified). For concealed sealants, butyl is recommended. For exposed 
sealants,  
polyurethane is recommended. During installation, cleanliness of the sealant  
substrate is important (particularly if polyurethane or silicone sealants are 
specified),  
as well as tooling of the sealant. ASTM E 2112 provides guidance on design of 
sealant  
joints, as well other information pertaining to installation of windows, 
including the  
use of sill pan flashings with end dams and rear legs (see Figure 6-46). It is  
recommended that designers use ASTM E 2112 as a design resource. 
Sealant joints can be protected with a removable stop as illustrated in Figure 
6-47. The  
stop protects the sealant from direct exposure to the weather and reduces the 
wind- 
driven rain demand on the sealant. 
 
Where water infiltration protection is particularly demanding and important, it 
is  
recommended that on-site water infiltration testing in accordance with ASTM E 
1105  
be specified. 
 
 
6.14 EXTERIOR-MOUNTED MECHANICAL, ELECTRICAL, AND  
COMMUNICATIONS EQUIPMENT 
 
Exterior-mounted mechanical (e.g., exhaust fans, HVAC units, relief air hoods, 
boiler  
stacks), electrical, and communications equipment (e.g., light fixtures, 
antennae,  
satellite dishes) are often damaged during high winds. Damaged equipment can im- 
pair the use of the school, the equipment can become missiles, and water can 
enter  
the facility where equipment was displaced (see Figures 6-19 and 6-48). 
Problems typically relate to inadequate equipment anchorage, inadequate strength 
of  
the equipment itself, and corrosion. 
 
 
6.14.1 Loads and Attachment 
 
Rooftop Equipment. Criteria for determining loads on rooftop equipment were 
added  
to the 2002 edition of ASCE 7. A minimum safety factor of three is recommended 
for  
the design of equipment anchorage. 
 
To anchor membrane fans, small HVAC units, and relief air hoods, the following  
minimum prescriptive attachment schedule is recommended: 
 
¥ For curb-mounted units, specify #14 screws with gasketed washers. 
¥ For curbs with sides less than 12 inches, specify one screw at each side of 
the curb. 
¥ For curbs between 12 inches and 24 inches, specify two screws per side.  
¥ For curbs between 24 inches and 36 inches, specify three screws per side.  
¥ For units that have flanges attached directly to the roof, attachment with #14 
pan- 
head screws is recommended. A minimum of two screws per side, with a maximum  
spacing of 12 inches on center is recommended. 
Figure 6-49 illustrates the use of supplemental securement straps to anchor  
equipment. The supplemental attachment was marginal; the straps were too light 
and  
the fasteners used to secure them were corroded. This illustrates the validity 
of the  
supplemental securement, and it also illustrates the need to execute the 
securement  
with attention to detail. In lieu of one screw at each end of the strap, two 
side-by-side  
screws offer a stronger and more reliable connection (this of course requires a  
slightly wider strap). 
 
Electrical and Communications Equipment.  Damage to exterior-mounted electrical  
equipment is infrequent, in large part, because of the small size of most 
equipment  
(e.g., disconnect switches). Exceptions are communication masts (see Figure 6-
50),  
surveillance cameras, service masts, and satellite dishes. These failures are 
typically  
caused by failure to perform wind load calculations and anchorage design. 
Service  
mast failure is typically caused by collapse of overhead power lines; this can 
be  
avoided by underground service. Where overhead service is provided, it is  
recommended that the service mast not penetrate the roof. Otherwise, a downed  
service line could pull the mast and rupture the roof membrane. 
 
ASCE 7 provides load calculation criteria for trussed towers. The ASCE 7 
criteria are  
consistent with ANSI/EIA/TIA-222-E. The ASCE 7 approach is a simplified 
procedure.  
The IBC allows use of either approach. ASCE 7 does not provide guidance for on-
site  
power distribution poles nor for light fixture poles. However, the National 
Electrical  
Safety Code, ANSI/C2 provides guidance for determining wind loads on power 
poles.  
The AASHTO Standard Specification for Structural Support for Highway Signs, 
Luminaries and  
Traffic Signals provides guidance for determining wind loads on light fixture 
poles. 
See Section 6.8.1 regarding siting of light fixture poles, power poles, and 
electrical  
and communications towers. 
 
 
 
6.14.2 Equipment Strength 
It is common for equipment components such as fan cowlings and access panels to  
be blown off during storms. Design of these elements is the responsibility of 
the  
equipment manufacturer. Although poor equipment performance has been  
documented, manufacturers have not offered enhanced equipment for high-wind  
regions. Therefore, it is incumbent upon the architect/engineer to give special  
design attention to equipment strength. 
 
Damage investigations have revealed that cable tie-downs have been effective in  
securing fan cowlings when a sufficiently strong cable and anchor details were 
used  
(see Figure 6-51). For fan cowlings less than 4 feet in diameter, 1/8-inch 
diameter  
stainless steel cables are recommended. For larger cowlings, use 3/16-inch 
diameter  
cables.  When the basic wind speed is 120 mph or less, specify two cables. Where 
the  
basic wind speed is greater than 120 mph, specify four cables. (As an 
alternative to  
cables, heavy stainless steel straps could be screwed to the cowling and curb.) 
To  
minimize leakage potential at the anchor point, it is recommended that the 
cables be  
anchored to the equipment curb (rather than anchored to the roof deck). The  
attachment of the curb itself also needs to be designed and specified.   
To minimize blow-off of equipment access panels, job-site modification will 
typically  
be necessary (such as the attachment of hasps and locking devices such as a  
carabineer). The modification details will need to be tailored for the 
equipment,  
which may necessitate detail design after the equipment has been delivered to 
the job  
site.  Alternatively, factored loads on the equipment could be specified, along 
with the  
requirement for the manufacturer to demonstrate compliance with the load  
requirement. 
 
 
6.14.3 Durability   
 
To avoid corrosion-induced blow-off, it is recommended that exterior-mounted  
mechanical, electrical, and communications equipment be nonferrous, stainless  
steel, or steel with minimum G-90 hot-dip galvanized coating for the equipment 
itself,  
equipment stands, anchors, and fasteners. When equipment with enhanced  
corrosion protection is not available, the designer should advise the school 
district  
that periodic equipment maintenance and inspection is particularly important to  
avoid advanced corrosion and subsequent equipment damage during a windstorm. 
The recommendations given in Sections 6.8 through 6.14 are summarized in Table 
6- 
1. 
 
 
 
 
6.15 SCHOOLS LOCATED IN HURRICANE-PRONE REGIONS  
 
 
The IBC, through ASCE 7, prescribes that exterior glazing in schools in wind-
borne  
debris regions be provided with wind-borne debris protection (either by use of  
laminated glass or shutters, as discussed in Section 6.15.6). Schools in 
hurricane- 
prone regions also have to be designed for a 100-year mean recurrence interval 
wind  
event if they are to be used as shelters. These are the only hurricane-related  
requirements currently in the IBC. These requirements do not provide adequate  
protection to occupants in a school during a hurricane, because the missile  
requirements only pertain to glazing. Hence, a code-compliant school can be  
designed, yet still allow the entrance of missiles through the roof or walls. To 
account  
for this deficiency, recommendations are given below regarding missile 
penetration  
through exterior walls and the roof. For a more conservative hurricane shelter, 
refer  
to FEMA 361. 
 
Publication 4496 by the American Red Cross (ARC) provides information regarding  
assessing existing buildings for use as hurricane shelters. Unless a school has 
been  
specifically designed for use as a shelter, it should only be used as a last 
resort and  
only if the school meets the criteria given in ARC 4496. 
Schools located in hurricane-prone regions should receive special design 
attention  
because of the unique characteristics of this type of windstorm. In addition to 
being  
capable of delivering very high winds, hurricanes can cause strong winds for 
many  
hours, which can eventually lead to fatigue failure. The direction of the wind 
can also  
change, thereby increasing the probability that the wind will approach the 
school at  
the most critical angle. Hurricanes also typically generate a large amount of 
missiles,  
which can be very damaging to schools and cause injury or death.   
For schools in hurricane-prone regions that will be used for a hurricane shelter  
and/or for emergency response after a storm, the following design parameters are  
recommended (these recommendations are in addition to the recommendations  
previously given in Sections 6.8 through 6.14): 
 
1.   During the design phase, the architect should determine from the school 
district  
whether or not the school will be designated or used as a shelter or emergency  
response facility. The school should only be used for a shelter if it was 
designed  
for that purpose.   
 
2.   For schools in coastal Alaska and other areas that experience frequent high 
wind  
events (such as parts of Colorado), several of the following recommendations are  
also applicable to these schools, with the exception of the wind-borne debris  
recommendations. 
 
 
6.15.1 Design Loads   
 
For the importance factor, use a value of 1.15. 
 
 
6.15.2 Structural Systems 
   
Because of the exceptionally good wind performance that reinforced cast-in-place  
concrete structures offer, a reinforced concrete roof deck and reinforced 
concrete  
and/or reinforced and fully grouted CMU exterior walls are recommended.   
In order to achieve enhanced missile resistance, the following roof decks are  
recommended, in descending order of preference: cast-in-place concrete, precast  
concrete, and concrete topping over steel decking. For exterior walls, the 
following  
are recommended: 6-inch (minimum) thick concrete reinforced with #4 rebars at 12  
inches on center each way, or 8-inch (minimum) thick fully grouted CMU 
reinforced  
with #4 rebars in each cell. 
 
 
6.15.3 Exterior Doors 
 
For glazing in doors, see the recommendations in Section 6.15.6. 
 
Although the ASCE-7 wind-borne debris provisions only apply to glazing within a  
portion of hurricane-prone regions, it is recommended that all schools that will 
be  
used for evacuation shelters within the entire hurricane-prone region comply 
with  
the following recommendation: To minimize the potential of missiles penetrating  
exterior doors and striking people within the school, it is recommended that 
doors  
without glazing and the unglazed portions of doors with glazing  be designed to  
resist the missile loads specified in ASTM E 1996 and that they be tested in  
accordance with ASTM E 1886. The test assembly should include the door, door 
frame  
and hardware. Further information on missile resistance of doors is found in 
FEMA  
361, Design and Construction Guidance for Community Shelters. 
6.15.4Non-load Bearing Walls, Wall Coverings, and Soffits   
In order to achieve enhanced missile resistance, the following types of exterior 
walls  
are recommended: reinforced cast-in-place concrete, or reinforced and fully 
grouted  
CMU.  
 
To minimize long-term problems with non-load bearing walls, wall coverings, and  
soffits, it is recommended that non-load bearing exterior walls, wall coverings, 
and  
soffits be avoided to the extent possible. Reinforced concrete or CMU offers 
greater  
reliability (i.e., they have no coverings that can be blown off).  
 
  
6.15.5 Roof Systems 
 
The following types of roof systems are recommended on schools in hurricane-
prone  
regions because they are more likely to avoid water infiltration if the roof is 
hit by  
wind-borne debris.  Also, the following systems are less likely to become 
sources of  
wind-borne debris: 
 
¥ In tropical climates where insulation is not needed above the roof deck: 1) 
liquid- 
applied membrane over cast-in-place concrete deck, or 2) modified bitumen  
membrane torched directly to cast-in-place concrete deck. 
¥ Install a secondary membrane over a concrete deck (if another type of deck is  
specified, a cover board may be needed over the deck). Seal the secondary  
membrane at perimeters and penetrations. Specify a minimum 2-inch thick rigid  
insulation and a layer of 5/8-inch thick glass mat gypsum roof board over the  
secondary membrane to absorb missile energy. If the primary membrane is  
punctured during a storm, the secondary membrane should provide watertight  
protection unless the roof is hit with missiles of very high energy. A modified  
bitumen membrane is recommended for the primary membrane because of its  
enhanced resistance to puncture by small missiles. 
¥ For an SPF roof system over a concrete deck, specify that the foam be a 
minimum of  
3 inches thick to avoid missile penetration through the entire layer of foam. 
¥ For a PMR, it is recommended that pavers weighing a minimum of 22 psf be  
specified. In addition, base flashings should be protected with metal. Parapets 
are  
recommended at roof edges. The parapet should be at least 3 feet high or higher 
if  
so indicated by ANSI/SPRI RP-4. Note: If the basic wind speed exceeds 130 mph, a  
PMR is not recommended on schools in hurricane-prone regions. 
¥ For structural metal roof panels with concealed clips, it is recommended that  
mechanically seamed ribs spaced at 12 inches on center over a concrete deck be  
specified. If a steel deck is specified, specify a self-adhering modified 
bitumen  
membrane and 3-inch thick rigid insulation, followed by the metal panels  
installed on wood nailers. At the self-adhering membrane laps, specify metal 
strips  
over the deck where the laps do not occur over the deck ribs, or specify a 
suitable  
cover board between the deck and self-adhering membrane. If the metal panels are  
punctured during a storm, the secondary membrane should provide watertight  
protection unless the roof is hit with missiles of very high energy. Note:   
Architectural metal panels are not recommended on schools in hurricane-prone  
regions. 
 
In order to avoid the possibility of roofing debris blowing off and striking 
people  
arriving at the school during the storm, the following types of roof coverings 
are not  
recommended:  aggregate surfacings (either on BUR [shown in Figure 6-11], 
single- 
plies [shown in Figure 6-8] or SPF), lightweight concrete pavers, cementitious-
coated  
insulation boards, slate, and tile (see Figure 6-52). Wind-borne debris from 
heavy roof  
coverings such as tiles have great potential to cause serious injury to people 
arriving  
at a school during a hurricane or other high wind event. 
 
Because mechanically attached and air-pressure equalized single-ply membrane  
systems are susceptible to massive progressive failure after missile impact (see 
Figure  
6-53), these systems are not recommended on schools in hurricane-prone regions.  
Fully adhered single-ply membranes are also very vulnerable to missiles (see 
Figure 6- 
54); therefore, they also are not recommended unless they are ballasted with 
pavers.  
 
 
6.15.6 Windows and Skylights 
 
ASCE 7 requires the use of impact-resistant glazing (i.e., laminated glass) or 
shutters  
in wind-borne debris regions. ASCE 7 refers to ASTM E 1996 for missile loads and 
to  
ASTM E 1886 for the test method to be used to demonstrate compliance with the E  
1996 load criteria. In addition to testing for impact resistance, the window 
unit is  
subjected to pressure cycling after missile impact to evaluate whether or not 
the  
window can still resist wind loads. 
If wind-borne debris glazing protection is provided by shutters, the glazing is 
still  
required by ASCE 7 to meet the positive and negative design air pressures. 
For those schools that desire to provide blast-resistant glazing, the windows 
and  
glazed doors can be designed to accommodate wind pressure, missile loads, and 
blast  
pressure. However, the window and door units need to be tested for missile loads 
and  
cyclic air pressure, as well as for blast. A unit that meets blast criteria will 
not  
necessarily meet the E 1996 and E 1886 criteria, and vice versa.  
With the advent of building codes requiring glazing protection in wind-borne 
debris  
regions, a variety of shutter designs have entered the market. Figure 6-55 
illustrates an  
effective shutter. A metal track was permanently mounted to the wall above and 
below  
the window frame. Upon notification of an approaching hurricane, the metal 
shutter  
panels were inserted into the frame and locked into position with wing nuts.  
Shutters typically have a lower initial cost than laminated glass. However, 
unless the  
shutter is permanently anchored to the school (e.g., an accordion shutter), 
space will  
be needed to store the shutters. Also, when a hurricane is forecast, costs will 
also be  
incurred each time shutters are installed and removed afterward. To avoid the  
difficulty of installing shutters on upper-level glazing, motorized shutters 
could be  
specified, although laminated glass may be more economical in these locations.  
 
 
6.15.7 Emergency Power 
 
Schools intended for use as shelters and/or emergency response after a storm 
should  
be equipped with an emergency generator. 
 
 
6.15.8 Construction Contract Administration 
 
It is important for the school district to obtain the services of a professional  
contractor who will execute the work described in the contract documents in a  
diligent and technically proficient manner.   
The frequency of field observations and extent of special inspections and 
testing  
should be greater than those employed on schools that are not designated as 
shelters. 
 
 
6.15.9 Periodic Inspections, Maintenance, and Repair 
 
The recommendations previously given for periodic and post-storm inspections,  
maintenance, and repair are critically important for schools used as shelters 
and  
emergency response after a storm because, if failure occurs, the risk of injury 
or death  
to occupants is great, and the needed continued operation of the school would be  
jeopardized. 
The recommendations given in Section 6.15 are summarized in Table 6-2.  These  
recommendations are in addition to those given in Sections 6.8 to 6.14, as  
summarized in Table 6-1. 
 
 
 
 
  
6.16 DESIGN FOR TORNADO SHELTERS 
 
Tornado risk assessment and tornado-prone regions were discussed in Section 6.7  
and the cost of tornado shelters was discussed in Section 6.5.2. Following up on 
those  
discussions, strong and violent tornadoes produce wind speeds that are 
substantially  
greater than those delivered by the strongest hurricanes; hence, the wind 
pressures  
that these tornadoes exert on buildings is tremendous and far exceed the minimum  
pressures required by building codes. In addition, strong and violent tornadoes 
can  
generate very powerful missiles (see Figure 6-56), including vehicles. The 
missile  
sticking out of the roof in the foreground of Figure 6-56 is a double 2-inch by 
6-inch.  
The portion sticking out of the roof is 13 feet long. It penetrated a ballasted 
ethylene  
propylene diene monomer (EPDM) membrane and approximately 3 inches of  
polyisocyanurate roof insulation and the steel roof deck. The missile laying on 
the  
roof just beyond is 2 inches by 10 inches by 16 feet long.  
Missile loads that are used for the design of tornado shelters are significantly 
greater  
than the missile loads used for the design of glazing protection in wind-borne 
debris  
regions of hurricane-prone regions. 
 
As discussed in Section 6.5.2, FEMA 361, Design and Construction Guidance for 
Community  
Shelters, includes software for assessing the benefit/cost ratio of 
incorporating  
specially designed tornado shelters within schools. In addition, it includes  
comprehensive information regarding the design of shelters. If shelter design is  
contemplated, use of FEMA 361 is recommended.  
 
Existing Schools without Tornado Shelters. Where the number of recorded F3, F4,  
and  
F5 tornadoes per 3,700 square miles is one or greater (see Figure 6-2), if the 
school  
does not have a tornado shelter, the best available refuge areas should be 
identified.  
FEMA 431, Tornado Protection, Selecting Refuge Areas in Buildings provides 
useful  
information for school administrators, and for architects and engineers who 
perform  
evaluations of existing schools. 
 
To minimize deaths and injuries of students, faculty, and other occupants, it is  
critically important that the best available refuge areas be pre-identified by a 
qualified  
architect/engineer.8  Once identified, those areas need to be clearly marked so 
that  
occupants can quickly seek refuge. Don't wait for the arrival of a tornado on 
the  
school grounds to try to find the best available refuge areas; by that time, it 
is too late.  
If refuge areas have not been pre-identified, occupants can easily take cover in 
areas  
that can become death traps (see Figure 6-57). 
When a true shelter is desired for a school that does not have one, retrofitting 
a  
shelter within the school can be very expensive. An economical alternative is an  
addition to the existing school that can function as a shelter as well as serve 
another  
purpose. This approach works well for smaller schools, but, for a very large 
school,  
construction of two or more shelter additions should be considered in order to  
reduce the time it takes to reach the shelter (often there is ample warning 
time, but  
sometimes an approaching tornado is not noticed until a couple of minutes before 
it  
strikes). 
 
The recommendations given in Section 6.16 are summarized in Table 6-3 . 
 
 
 
 
 
  
6.17 REMEDIAL WORK ON EXISTING SCHOOLS 
 
Section 6.6.1 discussed prioritizing and Section 6.6.2 discussed cost. Following 
up on  
those discussions, many existing schools need building envelope component  
strengthening or structural strengthening. The need for this work is due either 
to  
deterioration over time and/or inadequate facility strength at the time the 
school was  
built. 
   
It is prudent for school districts to have their existing facilities evaluated. 
This also  
applies to recently constructed schools that are located in an area where the 
basic  
wind speed is greater than 90 mph (peak gust), and those schools that will be 
used for  
emergency response after a storm and schools that will be used for a hurricane  
shelter. 
For new schools, areas of concern would typically be the building envelope and  
exterior-mounted mechanical, electrical, and communications equipment. By  
identifying weaknesses and prioritizing and executing the work, many failures 
can be  
averted. A proactive approach can save significant sums of money and decrease 
the  
number of instances when schools are impaired or immobilized after a storm.   
For roofs with weak metal edge flashing or coping attachment, face-attachment of  
the edge flashing/coping (as shown in Figure 6-39) is a cost-effective approach 
to  
greatly improve wind-resistance of the roof system. Fastening rooftop equipment 
to  
curbs is a cost-effective approach to avoid the type of problems shown in Figure 
6-19. 
During planned roof covering replacement, by tearing off the existing roof 
covering  
rather than re-covering, there is the opportunity to evaluate the structural 
integrity of  
the deck and deck attachment and upgrade its attachment if necessary. Many older  
decks are poorly attached (Figure 6-58); hence, if their attachment is not 
upgraded,  
blow-off of the deck and the new roof covering could occur. The two deck panels  
shown in Figure 6-58 blew away because their attachment to the roof structure 
was  
inadequate. An SPF roof covering was over the deck panels that blew away because 
of  
the characteristics of this type of covering, membrane propagation failure did 
not  
occur, as would have been the case with built-up, modified bitumen, or single-
ply roof  
membranes. Cementitious wood-fiber decks were commonly used on schools built in  
the 1950s and 1960s. Decks constructed during that era typically had very 
limited  
uplift resistance due to weak connections to the support structure.  
Design guidance pertaining to existing decks is presented in "Uplift Resistance 
of  
Existing Roof Decks:  Recommendations for Enhanced Attachment During Reroofing 
Work," RCI  
Interface, Thomas L. Smith, January 2003, pp. 14. 
Weak non-load bearing masonry walls, poorly connected precast concrete panels,  
long-span structures (e.g., at gyms) with limited uplift resistance, and weak 
glass  
curtain walls are common problems with many older schools. Although the 
technical  
solutions to these problems are not difficult, the cost of the remedial work is  
normally quite expensive. If remediation funds are not available, it is 
important to  
minimize the risk of injury and death by evacuating areas that have this type of  
construction when winds above 60 mph are forecast.  
For schools located in wind-borne debris regions, if the exterior glazing is not  
missile-resistant, equipping the openings with shutters is a cost-effective 
approach to  
provide protection. 
 
The recommendations given in Section 6.17 are summarized in Table 6-4. 
 
 
 
 
 
6.18 REFERENCES AND SOURCES OF ADDITIONAL INFORMATION  
 
American Institute of Architects, Buildings at Risk: Wind Design Basics for 
Practicing  
Architects, 1997. 
  
Federal Emergency Management Agency, Building Performance: Hurricane Andrew in  
Florida, FEMA FIA-22, Washington, DC, December 1992. 
 
Federal Emergency Management Agency, Building Performance: Hurricane Iniki in  
Hawaii, FEMA FIA-23, Washington, DC, January 1993. 
 
Federal Emergency Management Agency, Corrosion Protection for Metal Connectors 
in  
Coastal Areas, FEMA Technical Bulletin 8-96, Washington, DC, August 1996. 
 
Federal Emergency Management Agency, Typhoon Paka: Observations and  
Recommendations on Building Performance and Electrical Power Distribution 
System, Guam,  
U.S.A., FEMA-1193-DR-GU, Washington, DC, March 1998. 
 
Federal Emergency Management Agency, Hurricane Georges in Puerto Rico, FEMA 339,  
Washington, DC, March 1999. 
 
Federal Emergency Management Agency, Oklahoma and Kansas Midwest Tornadoes of  
May 3, 1999, FEMA 342, Washington, DC, October 1999. 
 
Federal Emergency Management Agency, Coastal Construction Manual, Third Edition,  
FEMA 55, Washington, DC, 2000. 
 
Federal Emergency Management Agency, Design and Construction Guidance for  
Community Shelters, FEMA 361, Washington, DC, July 2000. 
 
Federal Emergency Management Agency, Primer to Design Safe School Projects in 
Case of  
Terrorist Attacks, FEMA 428, Washington, DC, October 2003. 
 
Federal Emergency Management Agency, Tornado Protection, Selecting Safe Areas in  
Buildings, FEMA 431, Washington, DC, October 2003. 
 
National Research Council of Canada, Institute for Research in Construction, 
Wind  
Design Guide for Mechanically Attached Flexible Membrane Roofs, B1049, 2004. 
 
Rousseau, M.Z., Facts and Fictions of Rain-Screen Walls, Construction Canada, 
1990, pp. 40. 
Smith, Thomas L., "Insights on Metal Roof Performance in High-wind Regions,"   
Professional Roofing, February 1995, pp. 12 (available on-line at www.nrca.net). 
 
Smith, Thomas L., "Integrating a Lightning Protection System in a Roof System,"  
12th International Roofing and Waterproofing Conference Proceedings (CD),  
National Roofing Contractors Association, 2002. 
 
Smith, Thomas L., "Honing in on hangars,"  Professional Roofing, October 2002, 
pp. 32  
(available on-line at www.nrca.net). 
 
Smith, Thomas L., "Uplift Resistance of Existing Roof Decks:  Recommendations 
for  
Enhanced Attachment During Reroofing Work," RCI Interface, January 2003, pp. 14. 
Smith, Thomas L., "Detailing ASCE 7's changes," Professional Roofing, July 2003, 
pp. 26  
(available on-line at www.nrca.net). 
 
 
 
 
 
6.19 GLOSSARY OF WIND TERMS 
 
Basic wind speed. A 3-second gust speed at 33 feet above the ground in Exposure 
C.    
(Exposure C is flat open terrain with scattered obstructions having heights 
generally  
less than 30 feet.) Note: Since 1995, ASCE 7 has used a 3-second peak gust 
measuring  
time.  A 3-second peak gust is the maximum instantaneous speed with a duration 
of  
approximately 3 seconds. A 3-second peak gust speed could be associated with a 
given  
windstorm (e.g., a particular storm could have a 40-mile per hour peak gust 
speed), or  
a 3-second peak gust speed could be associated with a design-level event (e.g., 
the  
basic wind speed prescribed in ASCE 7). 
 
Building, enclosed. A building that does not comply with the requirements for 
open or  
partially enclosed buildings. 
 
Building, open. A building having each wall at least 80 percent open. This 
condition  
is expressed by an equation in ASCE 7. 
 
Building, partially enclosed. A building that complies with both of the 
following  
conditions: 
1. The total area of openings in a wall that receives positive external pressure 
exceeds  
the sum of the areas of openings in the balance of the building envelope (walls  
and roof) by more than 10 percent, and    
2. The total area of openings in a wall that receives positive external pressure 
exceeds  
4 square feet or 1 percent of the area of that wall, whichever is smaller, and 
the  
percentage of openings in the balance of the building envelope does not exceed  
20 percent. 
These conditions are expressed by equations in ASCE 7. 
 
Building, regular shaped. A building having no unusual geometrical irregularity 
in  
spatial form. 
Building, simple diaphragm. An enclosed or partially enclosed building in which 
wind  
loads are transmitted through floor and roof diaphragms to the vertical main 
wind- 
force resisting system. 
 
Components and cladding. Elements of the building envelope that do not qualify 
as  
part of the main wind-force resisting system. 
Escarpment. Also known as a scarp, with respect to topographic effects, a cliff 
or steep  
slope generally separating two levels or gently sloping areas.  
 
Exposure. The characteristics of the ground roughness and surface irregularities 
in  
the vicinity of a building. ASCE 7 defines three exposure categories - Exposures 
B, C,  
and D.  
 
Glazing. Glass or transparent or translucent plastic sheet used in windows, 
doors, and  
skylights. 
 
Glazing, impact-resistant. Glazing that has been shown by an approved test 
method to  
withstand the impact of wind-borne missiles likely to be generated in wind-borne  
debris regions during design winds. 
Hill. With respect to topographic effects, a land surface characterized by 
strong relief  
in any horizontal direction. 
 
Hurricane-prone regions. Areas vulnerable to hurricanes; in the U.S. and its 
territories  
defined as: 
1. The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed 
is  
greater than 90 miles per hour, and 
2. Hawaii, Puerto Rico, Guam, U.S. Virgin Islands, and American Samoa. 
 
Impact-resistant covering. A covering designed to protect glazing, which has 
been  
shown by an approved test method to withstand the impact of wind-borne missiles  
likely to be generated in wind-borne debris regions during design winds. 
Importance factor, I. A factor that accounts for the degree of hazard to human 
life  
and damage to property. The importance factor adjusts the mean recurrence 
interval.   
Importance factors are given in ASCE 7. 
 
Main wind-force resisting system. An assemblage of structural elements assigned 
to  
provide support and stability for the overall structure. The system generally 
receives  
wind loading from more than one surface. 
 
Mean roof height, h. The average of the roof eave height and the height to the 
highest  
point on the roof surface, except that, for roof angles of less than or equal to 
10  
degrees, the mean roof height shall be the roof eave height. 
 
Missiles. Debris that became or could become ingested into the wind stream.   
 
Openings. Apertures or holes in the building envelope that allow air to flow 
through  
the building envelope and that are designed as "open" during design winds. A 
door  
that is intended to be in the closed position during a windstorm would not be  
considered an opening. Glazed openings are also not typically considered an  
opening. However, if the building is located in a wind-borne debris region and 
the  
glazing is not impact-resistant or protected with an impact-resistant covering, 
the  
glazing is considered an opening. 
 
Ridge. With respect to topographic effects, an elongated crest of a hill 
characterized  
by strong relief in two directions. 
 
Wind-borne debris regions. Areas within hurricane-prone regions located: 
1. Within 1 mile of the coastal mean high water line where the basic wind speed 
is  
equal to or greater than 110 mph and in Hawaii; or 
2.  In areas where the basic wind speed is equal to or greater than 120 mph