Frequently Asked Questions About Building Science

Use the filters below to find answers to frequently asked questions about Building Science guidance regarding:

  • General Building Science questions
  • Substantial Damage Estimator (SDE) tool
  • Safe rooms
  • Floods
  • High winds
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If you need additional information, please email the FEMA Building Science Helpline or call at 866-927-2104.

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Please visit the Building Science Resource Library to reference all hazard-specific publications and guidance documents.

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Does the National Flood Insurance Program allow light switches and electrical outlets below the base flood elevation in enclosures and garages?

The National Flood Insurance Program (NFIP) limits switches, wiring, and receptacles below the base flood elevation (BFE) to the minimum necessary for life safety. Examples include smoke detectors, simple light fixtures, and switches and receptacles required for areas used for building access, parking, and storage. Floodwaters can corrode and short-circuit electrical system components, possibly leading to electrical shock. When subjected to high-velocity flow, electrical panels can be torn from their attachments by the force of breaking waves or the impact of floating debris. Some guidelines to follow are:

  • Install switches, receptacles, and wiring below the BFE on circuits fed from ground fault circuit interrupting (GFCI) breakers to ensure that the entire circuit is de-energized when infiltrated by floodwaters.
  • Install service connections (e.g., electrical lines, panels, and meters; telephone junction boxes; cable junction boxes) above the BFE. If the house is subject to coastal flooding, service connections should be installed on the landward side of interior piles or other vertical support members.
  • Use drip loops to minimize water entry at penetrations.
  • Never attach electrical components to breakaway walls.
  • If a portion of the area is above the BFE, install wiring and receptacles at a height above the BFE consistent with wet floodproofing methods.

Check with the local jurisdiction for additional requirements or restrictions on electrical equipment below the BFE.

For more information, see:

  • FEMA. 2017.  Protecting Building Utility Systems from Flood Damage: Principles and Practices for the Design and Construction of Flood Resistant Building Utility Systems. FEMA P-348, Edition 2 Washington, DC, February 2017.
  • FEMA. 2010. Home Builder’s Guide to Coastal Construction: Fact Sheet 8.3, Protecting Utilities. FEMA P-499. Washington, DC. December 2010.
Can the FEMA SDE Tool be used to evaluate both Substantial Damage and Substantial Improvement?

Yes. FEMA developed the SDE tool to help NFIP participants meet their obligation to evaluate damage or improvements before approving permits for rehabilitation, remodeling, and lateral or vertical additions. Although FEMA’s guidance on the SDE tool is geared toward estimating damages (as the name suggests), the tool can be used to evaluate improvements by substituting the cost of the improvements for the cost of repairs.

My House Has a Basement. Do I Need a Safe Room?

Some strong tornadoes have resulted in loss of floor framing, collapse of basement walls potentially leading to death and injuries to individuals taking refuge in a basement. The acceptable level of protection is an individual decision. A basement may be the safest place to seek shelter in a home without a safe room, but the basement will not provide the same level of protection as a safe room unless it has been designed and constructed in accordance with the criteria in FEMA P-361.

A basement is a good location to install or build a safe room, but access for handicapped or physically challenged individuals may be limited. The flood risk of your location may also help determine whether your basement is an appropriate place for a safe room. If your house or neighborhood is prone to flooding, the basement may not be suitable for taking refuge.

What Is the Minimum Square Footage per Person for a Residential Tornado and Hurricane Safe Room?

For residential safe rooms, the usable tornado safe room floor area should include the protected occupant area between the safe room walls at the level of fixed seating, where fixed seating exists, minus the area of sanitary facilities or other items that impede usage of the safe room area. Table 3 shows the minimum safe room floor area per occupant for residential tornado and hurricane safe rooms.

Residential Safe Room TypesMinimum Usable Floor Area per Safe Room Occupant
TornadoOne- and Two-Family Dwellings3 square feet
 Other Residential5 square feet
HurricaneOne- and Two-Family Dwellings7 square feet
 Other Residential10 square feet
Table 3. Occupant Density for Residential Tornado and Hurricane Safe Rooms

*See FEMA P-361 for more information on usable safe room floor area.

Besides FEMA Guidance, What Other Codes and Standards Apply to Safe Rooms?

FEMA P-361 provides the design criteria to be used with applicable building codes and code-referenced standards. This means that the underlying building code (such as the International Building Code® or International Residential Code®) applies and building construction must comply with the many items that are regularly governed by code requirements. Standards such as ASCE 7 also apply but are used in conjunction with the safe room design criteria described in FEMA P-361 to produce a structure capable of resisting loads much higher than those for normal buildings.

In December 2020, the International Code Council® (ICC®), with the support of the National Storm Shelter Association® (NSSA®), released a third edition of the consensus standard titled Standard for the Design and Construction of Storm Shelters, also known as the ICC 500. This standard provides minimum requirements for storm shelters and is referenced throughout Part B of FEMA P-361 which also includes FEMA Funding Criteria (required only for FEMA-funded safe rooms). If there are any conflicts between the codes and standards, the most conservative criteria should apply.

A summary of ICC 500 requirements and changes made to the 2020 edition compared to the 2014 edition can be found in Highlights of ICC 500-2020

Who Should I Contact To Inspect My Safe Room?

A design professional licensed in the state in which the safe room is installed can be contracted to inspect your safe room. Contact a local building official to determine who can properly inspect your safe room to verify that the safe room design criteria in FEMA P-361 have been met.

National Training and Education Division (NTED)'s National Preparedness Course Catalog

Search for available courses from three FEMA training organizations—Center for Domestic Preparedness (CDP), Emergency Management Institute (EMI) and National Training and Education Division (NTED)—easily in one location on the National Preparedness Course Catalog.

NTED provides first responders with high-quality training that enhances their skills for preventing, protecting, responding to, and recovering from manmade and natural catastrophic events. This platform:

  • Offers more than 150 courses to help responders build critical skills
  • Serves state, local, and tribal entities in 10 professional disciplines Instructs private sector and citizens in domestic preparedness including awareness, performance, and management and planning
  • Offers multiple course delivery methods: instructor led, train-the-trainers, conferences, seminars, and web-based
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