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Use the filters below to find answers to frequently asked questions about Building Science guidance regarding:
If you need additional information, please email the FEMA Building Science Helpline or call at 866-927-2104.
Please visit the Building Science Resource Library to reference all hazard-specific publications and guidance documents.
FEMA P-320 has prescriptive safe room plans for safe rooms sized between 8 feet x 8 feet x 8 feet tall and 14 feet x 14 feet x 8 feet tall. However, a safe room can be customized to meet your individual needs. Therefore, a safe room can be sized differently as long as it complies with current FEMA P-361 criteria. When changing any details of the prescriptive plans in FEMA P-320, consult a licensed design professional to verify that the modified plans still meet or exceed the design criteria of FEMA P-361. The design professional should be licensed in the state in which the safe room will be constructed or installed. If you are unsure if a safe room or storm shelter product meets FEMA P-361 criteria, you may contact your local building official or local or state emergency management office.
Additional information is available on our other FEMA Safe Room pages.
FEMA P-320 can be downloaded from the FEMA library website. The download contains both the publication and the design drawings.
When a question requires design guidance not covered in FEMA P-361 or ICC 500, the most current International Building Code® (IBC®) and International Residential Code® (IRC®) for one- and two-family dwellings (with references to the most recent versions of American Society of Civil Engineers [ASCE] 7, Minimum Design Loads for Buildings and Other Structures and ASCE 24, Flood Resistant Design and Construction) should be used as the design and construction criteria. When these criteria conflict, the most conservative criteria should apply. Safe rooms constructed in jurisdictions with no applicable codes should be designed and constructed per FEMA P-361 and the provisions of the 2018 or most current edition of the IBC®.
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:
Please consult a local building official to determine the applicable code requirements for your location.
References:
The only Special Flood Hazard Area (SFHA) zone in which fill can be used to elevate a structure above the base flood elevation (BFE) is Zone A. Fill cannot be used in Zone V. It is recommended that Coastal A Zones be treated as Zone V, and hence it is strongly recommended that fill not be used to elevate structures in Coastal A Zones.
Furthermore, not all Zone A areas freely allow the use of fill to elevate a home. The placement of fill in the SFHA can increase the BFE by reducing the soil’s ability to convey and store floodwaters. An increase in the BFE can result in increased flood damage to both upstream and downstream properties. To prevent these possible results, some communities prohibit the use of fill, require compensatory storage for filled areas, and/or identify a more restrictive floodway to preclude the use of fill in certain areas. For more information regarding using fill to elevate a structure in an SFHA, see Technical Bulletin 10, Ensuring That Structures Built on Fill In or Near Special Flood Hazard Areas Are Reasonably Safe from Flooding (FEMA, 2001). Check with the local jurisdiction on additional requirements on placing fill in the SFHA.
References: FEMA. 2001. Ensuring That Structures Built on Fill In or Near Special Flood Hazard Areas Are Reasonably Safe from Flooding. NFIP Technical Bulletin 10. Washington, DC, May 2001.
FEMA Technical Bulletin 5, Free-of-Obstruction Requirements for Buildings Located in Coastal High Hazard Areas (2008), provides guidance on the National Flood Insurance Program (NFIP) regulations concerning obstructions to floodwaters below elevated buildings and on building sites in Coastal High Hazard Areas (Zones V, VE, and V1-V30). Check with the local jurisdiction for additional information on free of obstruction requirements.
References: FEMA. 2008. Free-of-Obstruction Requirements for Buildings Located in Coastal High Hazard Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 5. Washington, DC. August 2008.
FEMA’s Technical Bulletin (TB) 9, Design and Construction Guidance for Breakaway Walls Below Elevated Buildings Located in Coastal High Hazard Areas (FEMA, 2008), provides guidance on the National Flood Insurance Program (NFIP) regulations concerning the design and construction of breakaway walls beneath elevated buildings in Coastal High Hazard Areas (Zones V, VE, and VI-V30). TB 9 presents three design methods consistent with NFIP regulations: a prescriptive design approach, a simplified design approach, and a performance-based design approach.
Additionally, Section 2.3.5 of FEMA P-55, Coastal Construction Manual (2011), discusses enclosures (including breakaway walls) and the unique situation they create in coastal construction. Check with the local jurisdiction for additional information on breakaway walls.
The FEMA floodplain management Web site also contains information on breakaway walls.
References:
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.
Yes. Per FEMA’s Technical Bulletin 1, Openings in Foundation Walls and Walls of Enclosures Below Elevated Buildings (FEMA, 2008), although openings should be installed on at least two sides of each enclosed area, it is not required. The only requirement is that there is a minimum of two openings on exterior walls to allow floodwaters to enter directly. In order to meet the requirement, the openings must be located so that the portion of the opening intended to allow for inflow and outflow is below the base flood elevation (BFE).
FEMA recommends, however, that openings be installed on at least two sides of each enclosed area to decrease the chances that all openings could be blocked with floating debris and to allow for more evenly distributed inflow of floodwater and draining of the enclosed area. It is recommended that the openings be reasonably distributed around the perimeter of the enclosed area unless there is clear justification for putting all openings on just one or two sides (such as buildings set into sloping sites).
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.
