Residential Safe Rooms Background and Research

Types of Residential Safe Rooms 
Residential safe rooms can take several forms:

* a room that normally serves
another purpose, such as a
bathroom or closet, and that
has been strengthened (or
"hardened") to resist wind
forces and the impacts of
windborne debris

* a room specifically designed
and constructed to serve as
shelter space only

* an underground space created
beneath the floor of a house or
an attached garage


In general, residential safe rooms can be built onsite in a new or existing home or can be 
manufactured units delivered to the site and installed. A safe room can be built or installed 
anywhere in a house, but it must be a "room within a room." That is, it's walls, ceiling, and 
floor must be structurally separate from the rest of the house, so that even if the surrounding 
house is destroyed, the safe room will remain intact. 
This brochure focuses on safe rooms built or installed inside a house, not on shelters built or 
installed elsewhere on the property. Properly designed and constructed in-residence safe rooms 
are preferable because they offer several advantages over exterior shelters: 

* The occupants of a house equipped with an
internal safe room can reach the shelter without
having to leave the house and risk exposure to high
winds and debris, lightning, or other storm conditions.

* An internal safe room can be reached more quickly and easily. 

* For those reasons, the occupants of a house with an internal safe
room are more likely to protect themselves adequately.


In some situations, however, building or 
installing an exterior shelter may be the only 
practical choice. For example, incorporating an 
in-residence safe room into an existing house 
may be impractical when extensive 
modifications to the structure of the house are 
necessary. For manufactured homes, an 
exterior shelter is usually the only practical 
solution. FEMA has not developed designs for 
exterior shelters, but the National Storm Shelter 
Association (NSSA) can provide information 
about exterior shelters that meet the engineering 
requirements established by FEMA. Visit the 
NSSA website at http://www.nssa.cc/. 

COMMUNITY WIND SHELTERS

As mentioned earlier, a residential safe room can serve more than
one purpose. Hardening a bathroom or closet to serve as a safe
room makes more efficient use of space than building a room that
serves as a safe room only. In smaller homes, providing for
alternative safe room uses can be an important consideration.

Additional information about in-residence safe rooms, including
design, construction, and related publications is available on the
Texas Tech University website at http://www.wind.ttu.edu/
inshelter/inshelte.asp.

Where Are Safe Rooms Needed? 
In areas subject to extreme-Wind Zones in the United States* wind events, 
homeowners should consider building a residential safe room. As noted in the following 
sections, wind hazards, such as those associated with tornadoes and hurricanes, vary 
throughout the United States. The decision to build a safe room will be based largely on 
the magnitude of the wind hazard in a given area and on the level of risk considered 
acceptable. 
FEMA Publication 320, Taking Shelter From the Storm: Building a Safe Room 
Inside Your House, contains tornado and hurricane statistics, wind speed and wind 
hazard data, a homeowner risk assessment worksheet, construction drawings for 
various types of residential safe rooms, and other information that will help a 
homeowner assess the risk in a specific area, determine the need for a safe room, 
and choose a safe room design. The construction drawings include all the 
FEMA 320	information a contractor would need to build a 
safe room that provides adequate protection from 
the most severe wind events. 
 

RESIDENTIAL SAFE ROOMS


Tornadoes - Understanding the Hazards 
A tornado is a violently rotating column of air that extends from a thunderstorm cloud to 
the ground. On average, more than 1,200 tornadoes have been reported nationwide each 
year since 1995. Since 1950, tornadoes have caused an average of 89 deaths and 1,521 
injuries annually, as well as devastating personal and property losses. As shown by the 
map, tornadoes occur primarily in the central and eastern portions of the United States. 
Tornadoes are rated by the National Weather Service according to the Fujita Damage 
Scale. Fujita ratings vary from F0, for light A tornado damage, to F5, for total destruction. 
All tornadoes produce high winds and carry windborne debris that can
pose a danger to lives and property. Violent tornadoes (those rated F4
and F5) are capable of tremendous destruction with wind speeds of up
to 250 mph near ground level. Violent tornadoes can rip buildings
 

Potential Impact and Damage From a Tornado 
Tornado damage paths over 50 miles long and over 1 mile wide have been reported. A 
good example of the destructiveness of tornadoes is the damage caused by the 67 
tornadoes that struck Oklahoma and Kansas on May 3, 1999, which included many F4 
and F5 tornadoes. This tornado outbreak resulted in 49 deaths and leveled entire 
neighborhoods. 
Additional information about the Oklahoma and Kansas tornadoes is available in the 
FEMA Building Performance Assessment Team report Midwest Tornadoes of May 3, 
1999, FEMA 342. 
 

Hurricanes - Understanding the Hazards 
A hurricane is a type of tropical cyclone (the general term for all 
weather systems that circulate counterclockwise in the Northern 
Hemisphere over tropical waters) originating in the Atlantic Ocean, 
Caribbean Sea, or Gulf of Mexico. Around the core of a hurricane, 
winds can grow with great velocity. As the storm moves ashore, it 
can push ocean waters inland while spawning tornadoes and 
producing torrential rains and floods. 
On average, 10 tropical storms (6 of which become hurricanes) develop each year in the 
Atlantic Ocean. Approximately five hurricanes strike the United States mainland every 3 
years; two of those storms will be major hurricanes (Category 3 or greater on the Saffir-
Simpson Hurricane Scale). 
Saffir-Simpson Hurricane Scale 
In the western Pacific, hurricanes are called typhoons and affect the Pacific Islands, including 
Hawaii, Guam, and American Samoa. Historically, typhoons have been classified by strength 
as either typhoons (storms with less than 150 mph winds) or super typhoons (storms with wind 
speeds of 150 mph or greater) rather than by the Saffir-Simpson Hurricane Scale. 
Although the highest wind speeds associated with hurricanes are not as great as those of the 
most severe tornadoes, hurricane winds and the debris they can carry are still extremely 
dangerous. The loss of life and property from hurricane-generated winds can be staggering. An 
example of a hurricane that caused severe wind damage is Hurricane Andrew, which made 
landfall in southeastern Florida in August 1992, generating strong winds and heavy rain over a 
vast portion of southern Dade County. The high winds associated with this Category 4 storm 
(131 mph to 155 mph) caused extensive damage in areas well beyond the reach of storm surge 
- areas where building or installing a residential safe room would be an appropriate and 
effective means of providing protection from high winds and windborne debris. 
When a hurricane threatens, weather services issue hurricane watches and warnings. A 
hurricane watch is issued when a hurricane is possible within 36 hours. A hurricane 
warning is issued when a hurricane is expected within 24 hours. An evacuation notice may 
be issued in conjunction with a hurricane warning.




COMMUNITY WIND SHELTERS

Safe Room Strength - Testing and Design 
For FEMA, the goal of safe room design and construction is to provide "near
absolute protection" from the forces of winds and debris during a storm with
winds as high as 250 mph. A safe room that provides near-absolute protection will
protect its occupants from death and injury; the safe room itself, however, may be
damaged by high winds or debris. As a result, repairs to the walls, ceilings, and
door of a safe room may be necessary after an extreme-wind event.

Clearly, to provide the desired level of protection, a safe room needs an
extremely strong structure to resist high-wind forces and an extremely
resistant envelope (walls, roof, and floor) to resist the impact of windborne
debris. To support the development of adequate safe room designs, the
Wind Engineering Research Center of Texas Tech University
conducted extensive laboratory tests of safe room construction
materials. The testing
program included
determining wind pressure
and debris impact loads
resulting from various
wind speeds and testing
the ability of building
materials (roof and wall
sections, doors, and door
hardware) to resist those
loads and impacts.

Of particular interest in the testing program was the impact of windborne debris on walls, 
doors, and roofs. Although much was known about the ability of small high-velocity 
projectiles to penetrate various materials, little prior testing had been conducted on the 
larger, slower moving objects likely to make up the most damaging windborne debris 
during a tornado. The Texas Tech research included firing a test missile - a 15-pound, 
12-foot-long 2x4 - at combinations of wall, ceiling, and door construction materials. The 
missile was fired at speeds of 67 mph and 100 mph to simulate the speeds of similar-
sized debris driven vertically downward and horizontally, respectively, by 250 mph storm 
winds. 

Safe rooms designs based on
the results of the Texas
Tech research typically
call for larger, stronger,
and a greater number
of construction
materials (e.g.,
concrete blocks,
reinforcing rods,
connectors, and
door hardware) than
designs for standard
residential construction.
The following are examples of wall and
door materials that passed the debris impact test
(further information is available on the Texas
Tech University website at
http://www.wind.ttu.edu/inshelter/inshelte.asp):

* 6-inch to 12-inch concrete masonry unit
walls, with vertical and horizontal reinforcement
and all cells poured full with 3,000-psi concrete

* 6-inch-thick horizontally and vertically
reinforced concrete

* plywood-covered wood-stud walls filled with
dry-stacked concrete blocks

* hollow metal doors and frames specifically tested
to meet FEMA 320 design forces

* 12-gauge or greater steel sheets combined with
plywood sheathing and wood studs


The results of the Texas Tech testing program served as the
basis for the safe room design guidelines, construction
drawings, and construction material lists presented in FEMA
320. Safe rooms built according to the FEMA 320 guidelines
and criteria are expected to provide near-absolute protection
for their occupants.


Other Considerations 
Although essential to successful performance, strength is not the sole
consideration in safe room design and construction. A residential safe room must also be
readily accessible, provide for the comfort of its occupants, and be equipped with 
emergency supplies.

 

Accessibility 
Residential safe rooms should be constructed in such a way that they are readily accessible to 
all family members or other occupants of the home. The path to the safe room should not be 
blocked with furniture or stored items. Also, if the safe room is normally used for another 
purpose (a closet for example), care should be taken not to clutter the floor with anything that 
could restrict the usable safe room space. Special needs, such as those of vision- or mobility-
impaired users, should be considered when decisions are made concerning the type and 
location of the safe room.


Occupant Comfort 
The primary goal of a residential safe room is to provide for the safety, not the comfort, of its 
occupants. The comfort of shelter occupants will depend largely on the amount of space 
provided per occupant and adequate lighting, water and food, and toilets. The amount of space 
required per person depends on the duration of occupancy. For this reason, the required space 
differs between safe rooms intended for tornado protection and those intended for hurricane 
protection. Historical data indicate that a tornado safe room will typically have a maximum 
occupancy time of 2 hours. By contrast, a hurricane safe room will have a maximum 
occupancy time of 36 hours. The recommended minimums for occupant space are 5 square 
feet per person for tornado safe rooms and 10 square feet per person for hurricane safe rooms. 
Note that these square footage figures are 
minimums; larger amounts of space are required 
for special situations. For example, the 5-square-
feet minimum for tornado safe rooms assumes 
that the safe room occupants will be standing for 
the duration of the event. Larger amounts of 
space are required for seated occupants and those 
with special needs, such as wheelchair users. 
Additional information about required safe room 
space is presented in FEMA Publication 320. 
Adequate supplies of water are essential for 
both tornado and hurricane safe rooms. Food 
should be provided in hurricane safe rooms, 
but is not a major consideration in tornado 
safe rooms, because of the short duration of 
use.


Emergency Supplies 
All residential safe rooms should be equipped 
with emergency supplies, including flashlights, 
fire extinguishers, first-aid kits, radios (including 
weather radios and extra batteries), and a 
signaling device (such as an air horn). 
 

 

New Construction vs. Retrofitting 
An additional consideration is whether a safe room will be built as new or retrofit
construction. Building a safe room as a part of a new home is generally more
efficient and economical than retrofitting
(modifying an existing home to meet specific
design requirements).

Retrofit safe room construction involves making all
changes necessary to strengthen an existing room
or area of a house so that it will provide the
required resistance to wind forces and debris
impact. This process could involve extensive
modifications to the foundation, frame, envelope,
connections, and other building components.
In addition, a residential safe room created
through retrofitting must be structurally separate
from the surrounding house (i.e., a room within
a room) so that damage to the house would not
affect the safe room. Although retrofit shelter construction
can be disruptive to building occupants, as well as more expensive than new
construction, it may be the only option in some circumstances.


Sources of Safe Room Information
Publications

FEMA has prepared a series of case studies that document the construction
of wind shelters, including residential safe rooms. The issues covered include
the need for shelters and safe rooms, design and construction, costs and
funding mechanisms, and performance in actual storms.

Other sources of wind shelter information include the following: 
Association Standard for the Design, Construction, and Performance of Storm Shelters, 
National Storm Shelter
Association, Lubbock, TX, 2001.
Design and Construction Guidance for Community Shelters (FEMA 361), FEMA, 
Washington, DC, July 2000.

Safe Room & Community Shelter Resource CD (FEMA 388-CD), FEMA, 
Washington, DC, October 2001.
Taking Shelter From the Storm: Building a Safe Room Inside Your House 
(FEMA 320), FEMA, Washington, DC,
August 1999.

Tornado Protection - Selecting Safe Areas in Buildings, Florida Department of 
Community Affairs, Tallahassee, FL,
March 2002.
Copies of FEMA publications are available from the FEMA Publications Distribution 
Center at 1-800-480-2520.

Related Websites 
FEMA Safe Rooms - http://www.fema.gov/mit/saferoom/ 
Texas Tech University Wind Science and Engineering Research Center - 
http://www.wind.ttu.edu/
National Storm Shelter Association - http://www.nssa.cc/