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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.

Browse the FAQs

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

No. FEMA does not approve, endorse, certify, or recommend any contractors, individuals, firms, or products. While a product may be in compliance with FEMA design guidance, contractors, individuals, or firms, shall not state they are, or produce products that are "FEMA approved" or "FEMA certified."

FEMA does not verify or certify design calculations for any product. The design professional who signs the certification attests that the product in question will meet the requirements specified on the certification. The design professional should be licensed in the state in which the product will be used. Note that any product must be properly installed for its intended use only.

Work on flood-damaged homes located in communities that participate in the National Flood Insurance Program (NFIP) is subject to specific requirements. If the flood-damaged home is in a floodplain and is substantially damaged (see definition below), the NFIP requires that reconstruction and repairs, termed substantial improvements (see definition below), be performed to bring the home into compliance with local floodplain management regulations. These regulations include elevating the home so that its lowest floor is at or above the base flood elevation (BFE). The local jurisdiction may require elevating the home higher than the BFE, to an elevation called the design flood elevation (DFE). Other requirements include using the proper type of foundation (depending on the flood zone in which the house is located), properly anchoring the home to the foundation, using flood-resistant materials, complying with limitations on the use of enclosed areas below the elevated home, and protecting utilities and equipment. Check with the local jurisdiction for additional requirements that must be met.

Reconstruction of a home that is destroyed or that has been so severely damaged that it must be rebuilt is considered construction of a new home, and new homes must comply with the local floodplain management regulations.

Definition: Substantial damage means damage of any origin for which the cost of restoring the structure to its before-damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred (FEMA, 2010).

Definition: Substantial improvement means any reconstruction, rehabilitation, addition, or other improvement of a structure for which the cost of the work equals or exceeds 50 percent of the market value of the structure before the start of construction of the improvement. This term includes structures that have incurred substantial damage regardless of the actual repair work performed (FEMA, 2010).

References: FEMA. 2010. Substantial Improvement/Substantial Damage Desk Reference. FEMA P-758. Washington, DC. May 2010.

Yes, FEMA has several publications for homeowners, design professionals, and builders that illustrate important concepts and best practices for constructing stronger, safer residential buildings in flood-prone areas in accordance with building codes and standards. All of these publications can be downloaded for free from FEMA’s Building Science Publications web site.

  • FEMA P-55, Coastal Construction Manual (FEMA, 2011) is a 2-volume publication that provides a comprehensive approach to planning, siting, designing, constructing, and maintaining homes in the coastal environment. Chapter 15 discusses retrofitting buildings for natural hazards.
  • FEMA P-259, Engineering Principles and Practices of Retrofitting Floodprone Residential Structures (FEMA, 2012) provides guidance for elevating an existing home. Chapter 5E provides guidance to determine the appropriate parameters for elevation and includes procedures and alternatives that apply to elevating buildings with a variety of foundation types. Chapter 3 includes a checklist (Figure 3-1) to help determine homeowner preferences for retrofitting options and a checklist (Figure 3-10) that a design professional may use to assess the initial building condition and determine whether the house is a good candidate for elevation.
  • FEMA P-312, Homeowner’s Guide to Retrofitting(FEMA, 2014) is a guide for homeowners to help them make decisions when retrofitting their homes and it introduces flood protection methods and building construction techniques. Chapter 5, Elevating Your Home, includes important elevation considerations and techniques. Please refer to Section 5.2.3, Elevating on an Open Foundation.
  •  FEMA P-499, Home Builder's Guide to Coastal Construction (FEMA, 2010) is a series of 37 fact sheets that provide technical guidance and recommendations concerning the construction of coastal residential buildings. Fact Sheet 9.1, Repairs, Remodeling, Additions, and Retrofitting – Flood, discusses requirements and recommendations when rebuilding or remodeling a property damaged by flood.

FEMA also produces a series of Technical Bulletins to provide guidance on the building performance requirements of the National Flood Insurance Program (NFIP). All of these publications can be downloaded for free from FEMA’s NFIP Technical Bulletins web site here.

In addition, FEMA offers several free publications that provide information on how to complete an Elevation Certificate. Although these publications are written for local building officials, surveyors, architects, and engineers who are authorized by law to certify elevation information on the certificate, the information can help homeowners understand the requirements for elevating buildings. Fore more information, visit National Flood Insurance Program Elevation Certificate and Instructions.

Please check with a local building official regarding the requirements for different flood zones and elevation in your area. Note that some communities may have more stringent requirements than the NFIP.

References: None.

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.

FEMA’s 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 and revised in 2010), classifies the flood damage-resistance of materials. Table 2 of TB 2 lists common building materials and classifies whether they are acceptable or unacceptable for use below the base flood elevation (BFE) in Special Flood Hazard Areas (SFHAs). Keep in mind, however, that flood damage-resistance may also be affected by the material’s specific application and the characteristics of the floodwaters. Sound judgment and knowledge of probable contaminants in local floodwaters are needed to select the proper materials.

Materials and products that are not listed in Table 2 may be used if accepted by the local official. For materials not listed in Table 2, manufacturers’ literature (i.e., specifications, materials safety data sheets, test reports) should be evaluated to determine if the product meets flood damage-resistance requirements; however, at this time, there are no specific tests or protocols for a manufacturer to use to test their materials for “flood damage-resistance.” Acceptance should be based on sufficient evidence, provided by the applicant, that the materials proposed to be used below the BFE will resist flood damage without requiring more than cosmetic repair and cleaning after being inundated by floodwater.

Note that community or State requirements that exceed those of the NFIP take precedence over what is specified in TB 2. Design professionals should contact the community to determine whether more restrictive criteria apply to the building or site in question.

References: FEMA. 2008, revised 2010. Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 2. Washington, DC, August 2008.

Information regarding Substantial Damage and Substantial Improvements can be found in FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference (FEMA, 2010). To participate in the National Flood Insurance Program (NFIP), communities must adopt and enforce regulations and codes that apply to new development in Special Flood Hazard Areas (SFHAs). Local floodplain management regulations and codes contain minimum NFIP requirements that apply not only to new structures but also to existing structures that have been Substantially Damaged or which are undergoing Substantial Improvement. FEMA P-758 provides practical guidance and suggested procedures to implement the NFIP requirements for Substantial Improvement/Substantial Damage.

In addition, FEMA has an NFIP Policy Index available online with basic information about Substantial Improvement, and Substantial Damage.

Definition: Substantial Damage means damage of any origin for which the cost of restoring the structure to its before-damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred (FEMA, 2010).

Definition: Substantial Improvement means any reconstruction, rehabilitation, addition, or other improvement of a structure for which the cost of the work equals or exceeds 50 percent of the market value of the structure before the start of construction of the improvement. This term includes structures that have incurred “substantial damage” regardless of the actual repair work performed (FEMA, 2010).

References: FEMA. 2010. Substantial Improvement/Substantial Damage Desk Reference. FEMA P-758. Washington, DC. May 2010.

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.

References:

FEMA’s Technical Bulletin (TB) 2, Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas (FEMA, 2008, revised 2010), provides guidance on the National Flood Insurance Program (NFIP) regulations concerning the required use of flood-damage resistant construction materials for building components located below the base flood elevation (BFE) in Special Flood Hazard Areas in both Zone A and Zone V. TB 2 provides a classification scheme for flood damage-resistant materials, as well as a table of common building materials, and describes whether they are allowed for use in construction below the BFE. Check with the local jurisdiction for additional requirements for use of materials below elevated buildings.

References: FEMA. 2008, revised 2010. Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 2. Washington, DC, August 2008.

Last updated November 19, 2021