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
Graphic
Email icon

If you need additional information, please email the FEMA Building Science Helpline or call at 866-927-2104.

alert - info

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

Browse the FAQs

Am I required to use the SDE tool when determining whether damage is considered to be Substantial Damage?

No. NFIP participants may use other methods of determining Substantial Damage but are encouraged to use the SDE tool because it provides a formal, systematic approach for determining Substantial Damage while also meeting all NFIP requirements.

Alternative methods for evaluating Substantial Damage and Substantial Improvement are available in FEMA P-758 and FEMA 213.

  • FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference (2010).
  • FEMA 213, Answers to Questions about Substantially Damaged Buildings (1991).
Do Any Local Jurisdictions Require Safe Rooms?

Local jurisdictions generally do not require residential safe rooms or storm shelters. However, some communities have offered incentives (such as reduced property taxes) for owners who wish to build a safe room or storm shelter for their home. Some state and local governments have engaged in grant programs with the federal government to partially subsidize the construction of both residential and community safe rooms.

The 2015, 2018, and 2021 International Building Code® (IBC®) require the construction of community storm shelters to be included when K-12 schools and first responder facilities are constructed in areas where the storm shelter design wind speed for tornadoes is 250 mph. These storm shelters must comply with the adopted code’s referenced edition of the International Code Council’s (ICC) Standard for the Design and Construction of Storm Shelters, also known as the ICC 500.

ICC 500 provides the minimum design and construction requirements for extreme-wind storm shelters and has been incorporated by reference as a standard to be followed for storm shelter design and construction in the 2009, 2012, 2015, 2018, and 2021 International Building Code (IBC) and International Residential Code (IRC), as well as the 2018 and 2021 International Existing Building Code (IEBC). Those involved in the design, construction, and maintenance of safe rooms should become knowledgeable about both FEMA guidance and ICC code and standard requirements that pertain to sheltering from extreme winds. Knowledge of the information in these publications will help those involved navigate local applicable codes, employ best practices to provide near-absolute protection, and apply for FEMA funds that may be available (if desired).

What Is the Cost of Installing a Safe Room in a New Home?

During the construction of a new home, the estimated basic cost to construct a safe room using the design plans in this publication ranges from approximately $9,400 to $13,100 for an 8-foot × 8-foot safe room and from $18,900 to $25,500 for a 14-foot × 14-foot safe room. The basic cost includes materials, labor and contingency but does not include the cost and installation of the safe room door assembly, which is addressed in the following section. Further, safe rooms installed in existing homes will be more expensive than those built as part of new construction. The cost of your safe room will vary depending on a variety of factors, including:

  • Safe room construction materials (CMU, concrete, wood, insulated concrete form [ICF])
  • Type of foundation on which the house is built (refer to Section 3.7)
  • Depth of footing; cost estimates are based on a minimum depth of 2 feet, 6 inches
  • Your location within the United States (because of regional variations in labor and material costs)
  • Whether you are building a safe room in a new home or retrofitting an existing home
  • Any added amenities (e.g., bathroom fixtures)

Prospective safe room owners are often surprised at the high cost of safe room door assemblies. Market research shows that entry level prices for properly tested and labeled residential safe room door assemblies are between approximately $2,500 and $3,200 (in 2021).

Residential prefabricated safe room costs, for just the units themselves and excluding site preparation and other costs, are approximately $5,000 to $6,000.

Section 4.3 of FEMA P-320 provides the assumptions and details of the cost estimates provided above.

What Design Guidance Should Be Used When Questions Arise Pertaining To Criteria Or Requirements Not Addressed by FEMA P-361 or ICC 500?

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®.

What Forces Should a Residential Safe Room Door Be Designed to Resist?

Residential safe room doors must be designed to resist pressures and loads resulting from a minimum wind speed of 250mph and be tested to resist the corresponding missile impacts and wind pressures. This means the doors must pass missile impact tests using a15-pound, 2 x 4 traveling at 100mph. Tornado residential safe room doors must undergo a static pressure test and hurricane residential safe room doors must undergo both static and cyclical pressure tests. For more detailed information on safe room doors, including test criteria, see FEMA P-361 and ICC 500. Helpful information on safe room doors can also be found in the Residential Tornado Safe Room Doors fact sheet.

Where can I find information on Substantial Damage and Substantial Improvements?

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.

Where can I find information on breakaway walls?

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:

  • FEMA. 2008. Design and Construction Guidance for Breakaway Walls Below Elevated Buildings Located in Coastal High Hazard Areas in Accordance with the National Flood Insurance Program. NFIP Technical Bulletin 9. Washington, DC, August 2008.
  • FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.
Are there any wind-related building code requirements or design standards pertaining to the attachment of rooftop equipment?

Rooftop equipment is typically torn off in high winds because equipment anchorage to the roof is inadequate, the strength of the equipment is inadequate, or the equipment is corroded. FEMA P-55, Coastal Construction Manual (FEMA 2011), includes prescriptive attachment recommendations for small equipment (see Section 12.8.2.1). Such equipment may include exhaust fans, vent hoods, and some residential air conditioning units. FEMA P-55 also provides guidance on job-site strengthening of fan hoods and cowlings through the use of stainless steel cables.

If the mounted equipment is more than 30 inches above the curb, the attachment design should be based on the calculated wind loads from ASCE 7-10, Minimum Design Loads for Buildings and Other Structures. Chapter 29 of ASCE 7-10 contains provisions for determining the lateral force and vertical uplift force on rooftop equipment for buildings with a mean roof height less than or equal to 60 feet. Figure 29.5-1 of ASCE 7-10 provides a force coefficient for chimneys, tanks, rooftop equipment, and similar structures. The force coefficient, Cf, is applied to equations found in Section 29.5.1 of ASCE 7-10 to calculate both the lateral and uplift design wind forces. The lateral force is based on the vertical area of the equipment as projected on a vertical plane perpendicular to the direction of the wind. The uplift force is based on the horizontal area of the equipment as projected on the horizontal plane above the equipment and parallel to the direction of the wind.

To avoid corrosion problems, FEMA P-55 (Section 12.8.2.1) recommends nonferrous metals, stainless steel, or steel with a minimum G-90 hot-dip galvanized coating for the equipment itself, equipment stands, and equipment anchors when located within 3,000 feet of a body of water producing salt spray. Stainless steel fasteners are also recommended.

References:

  • ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE 7-10, Reston, VA, May 2010.
  • FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.
What versions of Windows support the SDE tool?

The SDE tool can be installed on computers running Microsoft© operating systems Windows 7©, and Windows 8©, and Windows 10©. For more information, refer to Section 2 of the FEMA Substantial Damage Estimator (SDE) User Manual and Field Workbook.

Does FEMA Verify Or Certify Design Calculations Published By Manufacturers For Their Products?

No. FEMA does not verify or certify design calculations for any product. The registered design professional who signs the certification attests that the product in question meets the requirements specified on the certification. The design professional should be licensed in the state in which the product will be used. All products must be properly installed for their intended use(s) only.

Last updated