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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Where do I measure my bottom floor to meet BFE requirements?

How to measure your bottom (lowest) floor and whether your home meets the BFE requirements is determined by your community’s building codes and floodplain management regulations, and the flood zone in which your home is located.

The term “lowest floor” is defined by the NFIP and building codes. It refers to the portion of the building that is raised above the ground on an elevated foundation. In Zone A, the elevation of the “lowest floor” is measured at the top of the floor of the elevated building. In Zone V, the elevation is measured at the bottom of the lowest horizontal structural member (beam) that supports the elevated building. 

To comply with the NFIP and building codes, a building must have its lowest floor elevated to or above the specified elevation, usually the BFE or higher.  The only way to know for sure if your home is elevated high enough to comply with the requirements is to have a licensed surveyor prepare an Elevation Certificate.  If your home was built in accordance with floodplain management rules in effect at the time it was constructed, your community may have a record of the surveyed information.

References: FEMA. 2012. Quick Reference Guide: Comparison of Select NFIP and Building Code Requirements for Special Flood Hazard Areas. Washington, DC. March 2012.

Are interior enclosed spaces required to have flood openings? And do flood openings on interior walls count toward the "net open area" requirements?

Although flood openings on interior walls are not explicitly required by the NFIP, FEMA Technical Bulletin (TB) 1, Openings in Foundation Walls and Walls of Enclosures (2008), suggests that interior enclosed areas that do not have any exterior walls should have openings to ensure water reaches all enclosed areas in order to minimize unbalanced hydrostatic forces (top of page 17). This is especially important if one of the interior walls is load bearing. It is recommended that you use the same number of openings that would be used if the interior enclosed area had an exterior wall.

Flood openings installed on interior walls do not count towards the required total net area of flood openings. Although flood openings on interior walls do not count towards the required total net area of flood openings, it is recommended to install flood openings on interior walls between enclosed areas. Installing flood openings on interior walls is important to relieve unbalanced hydrostatic forces on the wall.

References: FEMA. 2008. Openings in Foundations Walls and Walls of Enclosures in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 1. Washington, DC. August 2008.

How can the wind and water resistance of roof soffits in homes be improved?

Technical Fact Sheet No. 7.5 in FEMA P- 499, Home Builder’s Guide to Coastal Construction (FEMA 2010a), provides retrofit criteria for each type of attic ventilation opening, including soffits. The most critical soffit installations are those with vinyl or aluminum soffit panels. Aluminum soffit panels may also be vulnerable because of aluminum’s corrosion potential in an environment with salt-laden air. If the house is within 3,000 feet of a body of water that produces salt spray, it is recommended that aluminum soffits be completely removed and replaced with a soffit system installed per the guidance of Technical Fact Sheet No. 7.5. Furthermore, Figure 4-12 of FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010b), shows a typical soffit detail for retrofitting existing soffits to improve wind and water resistance. It should be noted that while many homes may have different soffit configurations than shown in Figure 4-12, the basic intent of the retrofit in the figure—reduction of long spans by installation of intermediate supports and application of continuous edge support—should be applied in any situation. For improved wind and water resistance, soffits should be secured using sealant and screws as described in Technical Fact Sheet No. 7.5. The selected soffit product may have more restrictive installation instructions when installed in high-wind regions, in which case the more restrictive installation method should be followed.


  • FEMA. 2010a. Home Builder’s Guide to Coastal Construction. FEMA P-499. Washington, DC. December 2010.
  • FEMA. 2010b. Wind Retrofit Guide for Residential Buildings. FEMA P-804. Washington DC. December 2010.
Do I need administrative rights to install the SDE tool on my computer?

A6. Depending on the set-up of the user’s computer, administrative rights may be required for the installation of the tool. The need for administrative rights is set by the agency, community, or other entity that is responsible for the security and maintenance of the user’s computer. The installation options and the need for administrative rights are available in the FEMA SDE Read Me - SDE 3.0 Tool Installation Guide and the FEMA Substantial Damage Estimator (SDE) User Manual and Field Workbook. Both documents are available on the same website.

Does FEMA Approve, Endorse, Or Certify Any Products?

Due to federal regulations, FEMA does not endorse, approve, certify, or recommend any contractors, individuals, firms, or products. Contractors, individuals, or firms shall not claim they or their products are “FEMA approved” or “FEMA certified.” You should work with a registered design professional, such as an architect or engineer, who is familiar with safe rooms to verify that your safe room meets or exceeds current FEMA criteria.

As a Homeowner, Can I Build the Safe Room on My Own?

A homeowner who builds a safe room should be skilled in construction. It should be noted that the safe room door assembly cannot be constructed by a homeowner or contractor because ICC 500 requires that all storm shelter impact protective systems (including safe room door assemblies) demonstrate compliance with the standard’s testing requirements by labels attached to approved doors by third-party certification agencies. For more information on residential safe room doors, please refer to response provided for the question “Where Can I Find Doors And Hardware For My Safe Room?"

In addition to site-built residential safe rooms, there are also many prefabricated options available from safe room manufacturers. As noted in FEMA P-320 Section 4.2.2, anchorage of prefabricated safe rooms is critical to their performance in extreme wind events. More information on prefabricated safe room installation needs for above- and in-ground units  can also be found in the Foundation and Anchoring Criteria for Safe Rooms fact sheet.

Where Can I Find Additional Information and Plans for Safe Room Construction?

Additional information is available on our other FEMA Safe Room pages.

Should The Door Of A Safe Room Swing Inward Or Outward?

A common misconception about safe room doors is that they must swing in a particular direction – inward or outward. According to ICC 500, the pressure testing on a door must be conducted away from the door stop, meaning that the door is pressure-tested in the weakest condition regardless of being in-swinging or out-swinging. Additionally, a door must undergo the missile impact resistance testing in the configuration that will be used for installation.

Beyond code requirements, both inward- and outward-swinging doors have benefits. For example, inward-swinging doors are less likely to be blocked by debris, while outward-swinging doors provide more usable space within the safe room.

In some states or communities, the applicable building code may require that doors swing in a particular direction. For information on code requirements for your jurisdiction, contact a local building official or licensed design professional in your area.

Is there FEMA funding available for my project?

For project eligibility questions, please contact your State Hazard Mitigation Officer (SHMO).

Is standard (untreated), solid dimension lumber flood damage-resistant as defined by the National Flood Insurance Program (NFIP)?

The use of standard, solid dimension lumber is acceptable for structural use below the base flood elevation (BFE) per FEMA’s NFIP. Table 2 of NFIP Technical Bulletin (TB) 2, Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program (FEMA, 2008, revised 2010), lists solid, standard dimension lumber as an “acceptable” flood damage-resistant material. However, the same table classifies solid, standard lumber as unacceptable when applied as finish or trim material below the BFE. Before using standard, dimension lumber below the BFE though, it is critical to ensure that this application is acceptable per local regulations and the locally adopted codes. Codes and standards may have more stringent regulations (e.g., only using decay-resistant or preservative treated wood below the BFE) than those in TB 2. This is reiterated in the footnote that was added in 2010 below Table 2 in TB 2 which reads:

“In addition to the requirements of TB 2 for flood damage resistance, building materials must also comply with any additional requirements of applicable building codes. For example, for wood products such as solid 2x4s and plywood, applicable building code requirements typically include protection against decay and termites and will specify use of preservative-treated or decay-resistant wood for certain applications. Applications that require preservative-treated or decay-resistant species include wood in contact with the ground, wood exposed to weather, wood on exterior foundation walls, or wood members close to the exposed ground. In some cases, applicable building code requirements (such as those in ASCE 24-05 and IRC 2006) do not reflect updated guidance in TB 2 and specify that all wood used below the design flood elevation be preservative-treated or naturally decay-resistant regardless of proximity to ground or exposure to weather. (Revision made in October 2010)”

After Hurricane Katrina, it was observed that untreated wood materials seemed to perform acceptably as long as they had the chance to air dry before mold growth began. To facilitate the restoration of flooded buildings, FEMA 549, Hurricane Katrina in the Gulf Coast: Mitigation Assessment Team Report (FEMA, 2006), recommends that building owners:

  • Open windows and doors to maximize air flow
  • Remove contents for restoration or disposal
  • Remove porous wall materials, fibrous wall insulation, carpeting, vinyl flooring, and electrical components that were damaged by floodwaters
  • Thoroughly clean and sanitize interior surfaces
  • Allow sufficient time for drying prior to initiating reconstruction activities

Please consult a local building official to determine the applicable code requirements for your location.


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