Frequently Asked Questions - Building Science

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Below are frequently asked questions regarding FEMA Building Science Flood and Wind Mitigation guidance, as well as the FEMA Substantial Damage Estimator (SDE) Tool. If you need additional information, please contact the FEMA Building Science Helpline by email at FEMA-BuildingScience@fema.dhs.gov or by calling 866-927-2104. Please allow up to 5 business days for a response.

Please find additional frequently asked questions regarding FEMA safe rooms at the Safe Room FAQs page.

GENERAL 
Q1. Is there FEMA funding available for my project? 
Q2. Does FEMA approve, endorse, or certify any products? 
Q3. Does FEMA verify or certify design calculations published by manufacturers for their products?

FLOOD
Q1. When does a flood-damaged home need to be elevated? 
Q2. Does FEMA have existing guidlines for elevating a home in a flood zone?
Q3. Where do I measure my bottom floor to meet base flood elevation (BFE) requirements?
Q4. Where can I find information on substantial damage and substantial improvements?
Q5. Where can I find a list of materials compliant with the National Flood Insurance Program (NFIP) regulations for use below the BFE? 
Q6. Is standard (untreated), solid dimension lumber flood damage-resistant as defined by the National Flood Insurance Program (NFIP)?
Q7. Where can I find information on materials that are acceptable for framing, sheathing, and finishes for enclosures below elevated buildings? 
Q8. Where can I find information on flood openings for enclosures below the base flood elevation (BFE)? 
Q9. How is the net open area of a flood vent measured?
Q10. Can the flood opening requirement be satisfied when only one wall is accessible below the base flood elevation? 
Q11. Where can I find information on breakaway walls? 
Q12. Where can I find information on the “Free of Obstruction” requirements in Zone V? 
Q13. In which Special Flood Hazard Area zones can fill be used to elevate a home? 
Q14. What are the requirements for ducts that are installed between floor joists on an elevated building? 
Q15. Does the National Flood Insurance Program allow light switches and electrical outlets below the base flood elevation in enclosures and garages? 
Q16. I have a row house, how do I elevate it?

WIND
Q1. How can I protect the roof of my home from water intrusion?
Q2. How can the wind and water resistance of roof soffits in homes be improved? 
Q3. Are there any wind-related building code requirements or design standards pertaining to the attachment of rooftop equipment? 
Q4. Does FEMA have any publications that address design and construction guidance for high wind?

FEMA SUBSTANTIAL DAMAGE ESTIMATOR (SDE) TOOL
Q1. Why do I need to determine substantial damage or substantial improvement for structures located in the Special Flood Hazard Area (SFHA)?
Q2. Can the FEMA SDE Tool be used to evaluate both substantial damage and substantial improvement?
Q3. Am I required to use the SDE Tool when determining whether damage is substantial?
Q4. What resources are available from FEMA regarding substantial damage and substantial improvement?
Q5. What is the current version of the SDE Tool and the User Manual? 
Q6. Why do I need administrative rights to install the SDE Tool on my computer? 
Q7. Can I install the SDE Tool in Windows 7? 
Q8. How should I address the following SDE error message, which cites duplicate records?
Q9. What causes a “GDI+” or “Out of Memory” error when generating reports from the SDE Tool? 

GENERAL

Q1. Is there FEMA funding available for my project?

A1. For project eligibility questions, please contact your State Hazard Mitigation Officer (SHMO).

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Q2. Does FEMA approve, endorse, or certify any products?

A2. No. Federal policy does not allow FEMA to approve, endorse, certify, or recommend any products. While a product may be in compliance with FEMA design guidance, any language from manufacturers stating their product is “FEMA approved” or “FEMA certified” is incorrect.

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Q3. Does FEMA verify or certify design calculations published by manufacturers for their products?

A3. 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.

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FLOOD

Q1. When does a flood-damaged home need to be elevated?

A1. 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. 

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Q2. Does FEMA have existing guidelines for elevating a home in a flood zone?

A2. 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 floodprone areas in accordance with building codes and standards. All of these publications can be downloaded for free from FEMA’s Building Science Publiations 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, 2009) 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 5.3.3, 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. These publications can be accessed from FEMA Elevation Certificate web site.

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.

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Q3. Where do I measure my bottom floor to meet BFE requirements?

A3. 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.

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Q4. Where can I find information on substantial damage and substantial improvements?

A4. 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 (SD) or which are undergoing substantial improvements (SI). FEMA P-758 provides practical guidance and suggested procedures to implement the NFIP requirements for SI/SD.

In addition, FEMA has an NFIP Policy Index available online with basic information about SI, and SD.

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.

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Q5. Where can I find a list of materials compliant with the National Flood Insurance Program (NFIP) regulations for use below the base flood elevation?

A5. 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 and 2010. Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. Technical Bulletin 2. Washington, DC, August 2008.

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Q6. Is standard (untreated), solid dimension lumber flood damage-resistant as defined by the National Flood Insurance Program (NFIP)?

A6. 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. 2006. Hurricane Katrina in the Gulf Coast: Mitigation Assessment Team Report – Building Performance Observations, Recommendations, and Technical Guidance. Washington, DC, July 2006.

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. Technical Bulletin 2. Washington, DC, August 2008.

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Q7. Where can I find information on materials that are acceptable for framing, sheathing, and finishes for enclosures below elevated buildings?

A7. FEMA’s Technical Bulletin (TB) 2, Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas (FEMA, 2008), 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. 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.

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Q8.Where can I find information on flood openings for enclosures below the base flood elevation (BFE)?

A8. FEMA’s Technical Bulletin (TB) 1, Openings in Foundation Walls and Walls of Enclosures Below Elevated Buildings (FEMA, 2008) provides National Flood Insurance Program (NFIP) requirements and guidance for installing flood openings in enclosures located below the base flood elevation (BFE) in Zones A, AE, A1-A30, AR, AO, and AH for a variety of different foundation types. Check with the local jurisdiction for additional information on flood openings.

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.

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Q9. How is the net open area of a flood vent measured?

A9. FEMA Technical Bulletin (TB) 1, Openings in Foundation Walls and Walls of Enclosures (2008), states that the term “net open area” refers to the permanently open area of a non-engineered opening. The National Flood Insurance Program (NFIP) regulation permits flood openings that are equipped with coverings or dividers as long as they allow the automatic exit and entry of floodwaters. When calculating the net open area of a flood opening with a cover, coverings that have solid obstructions such as grilles, fixed louvers, or faceplates must be considered. Figure 14 of TB 1 shows a standard air vent faceplate that provides 42 square inches of net open area. This number is derived by multiplying the 0.5-inch width of the openings times the 6.5-inch height of the openings times the 13 total openings. Such estimates may be used when no other data are available.

According to FEMA TB 1, manufacturers of devices intended for use as standard air vents typically indicate the number of square inches that each device provides for airflow (either stamped onto the metal frame or noted on the packaging). This number should be used for the net open area when these devices are installed as non-engineered flood openings. To qualify as flood openings that permit automatic entry and exit of floodwaters, openings must not have solid covers installed. Similarly, typical air vent devices used as flood openings designed to be opened and closed manually must be disabled permanently in the open position.

Insect screens that do not impede the entry and exit of floodwaters are allowed and do not affect the determination of net open area. If a community has adopted the International Building Code (IBC) or International Residential Code (IRC), a screen is required to cover ventilation openings to keep out animals and insects. The IBC and IRC provide a list of acceptable covering materials. The commentaries that accompany the codes note that some covering materials may reduce the gross open area by up to 50 percent, in turn reducing the net open area. As a result of this reduction, in communities where floodwaters are expected to carry debris, local officials may determine that additional openings are required to compensate for the possibility that some openings may become clogged with debris.

FEMA TB 1, page 27, presents the equation that can be used to determine the area of an engineered flood vent opening. The equation is taken from American Society of Civil Engineers (ASCE) 24-05, Flood Resistant Design and Construction (2005).

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.

American Society of Civil Engineers (ASCE). 2005. Flood Resistant Design and Construction. ASCE 24-05.

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Q10. Can the flood opening requirement be satisfied when only one wall is accessible below the base flood elevation?

A10. 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.

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Q11. Where can I find information on breakaway walls?

A11. 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.

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Q12. Where can I find information on the “Free of Obstruction” requirements in Zone V?

A12. 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.

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Q13 In which Special Flood Hazard Area zones can fill be used to elevate a home?

A13. 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.

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Q14. What are the requirements for ducts that are installed between floor joists on an elevated building?

A14. The National Flood Insurance Program (NFIP) requires that the heating, ventilation, and air conditioning (HVAC) system in a new or substantially improved structure in a Special Flood Hazard Area (SFHA) be elevated above the base flood elevation (BFE) or designed so that floodwaters cannot infiltrate or accumulate within any component of the system.

All structural and nonstructural building components at or below the BFE must be constructed of materials resistant to flood damage. Flood damage-resistant materials must be used for all building elements subject to exposure to floodwaters, including floor joists, insulation, and ductwork. Building components that do not use flood damage-resistant materials must be elevated above the BFE. A flood damage-resistant material is defined as any building material capable of withstanding direct and prolonged contact with floodwaters without sustaining significant damage. Prolonged contact is defined as contact with floodwaters for a minimum of 72 hours and significant damage refers to any damage requiring more than low-cost cosmetic repair (such as painting). The cost of repair should be less than the cost of replacement for the material or system. This requirement applies regardless of the expected or historical flood duration.

The NFIP does not recommend installing ductwork below the BFE in any new or substantially improved structure located in an SFHA. There is no known cost-effective technique for designing air ducts to keep floodwaters from entering or accumulating within the system components during a flood. If ductwork must be installed below the BFE, it should be minimized as much as possible. The ducts must be composed of impermeable and watertight material, such as welded seamless ductwork or large-diameter PVC pipe. Such material is expensive, but practical when a short length of ductwork descends below the BFE.

In a Coastal High Hazard Area (CHHA), structures in the Coastal A Zone (areas in Zone A that are subject to wave heights more than 1.5 feet) and Zone V can be significantly damaged by wave action. In Zone V, the lowest horizontal structural member must be installed at or above the BFE. Anything below the BFE is regarded as an obstruction and can result in increased flood insurance premiums. Ductwork below the BFE should be avoided at all costs in Zone V and Coastal A Zones because it is difficult to design and construct a ductwork system that will sustain not only the hydrostatic loading, but also the additional hydrodynamic, wave forces and debris impact loads in these flood zones.

For more information on this topic, see:

  • FEMA. 1999. Protecting Building Utilities from Flood Damage: Principles and Practices for the Design and Construction of Flood Resistant Building Utility Systems. FEMA P-348, Edition 1. Washington, DC, November 1999.
  • FEMA. 2001. Crawlspace Construction for Buildings Located in Special Flood Hazard Areas. NFIP Technical Bulletin 11. Washington, DC, November 2001.
  • FEMA. 2008. Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas. NFIP Technical Bulletin 2. Washington, DC, August 2008.
  • FEMA. 2010. Substantial Improvement/Substantial Damage Desk Reference, FEMA P-758. Washington, DC. May 2010.
  • FEMA. 2010. Home Builder’s Guide to Coastal Construction. FEMA P-499. Washington, DC. December 2010.
  • National Archives and Records Administration. 2010. 44 Code of Federal Regulations Ch. 60.3(a) through (ef), “Flood Plain management Criteria for Flood-prone Areas.” Washington, DC. November 2010.

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Q15. Does the National Flood Insurance Program allow light switches and electrical outlets below the base flood elevation in enclosures and garages?

A15. 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. 1999. Protecting Building Utilities from Flood Damage: Principles and Practices for the Design and Construction of Flood Resistant Building Utility Systems. FEMA P-348, Edition 1. Washington, DC. November 1999.
  • FEMA. 2010. Home Builder’s Guide to Coastal Construction: Fact Sheet 8.3, Protecting Utilities. FEMA P-499. Washington, DC. December 2010.

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Q16. I have a row house, how do I elevate it?

A16. Since the late 19th Century, row houses have been a common style in New York and New Jersey. Many of these buildings consist of a lower level or walk-out basement (not a basement per the NFIP) and 2 or 3 stories of upper floors.

If Substantially Damaged, row houses in mapped flood hazard areas have to be brought into compliance with the requirements for new homes. There may be several ways compliance can be achieved, each depending on several factors, including how high the BFE is above the ground. For example, it may be necessary to abandon the lowest level and then modify the upper floors.  If the next lowest floor is below the BFE or local elevation requirement, the floor system may need to be removed and reconstructed to appropriate elevations.  The figure below illustrates the scenario where the lowest floor would be partially filled to grade (with the remaining area on the lowest floor being wet floodproofed and used as storage), and the top two floors would each be raised.

High ceilings typical of older row homes may make it easier to meet the requirements by building a “false floor” to create a crawlspace, although doing this will reduce ceiling heights while retaining the original floor space of the upper levels. It may not be possible to modify common walls (party walls) but the exterior walls at the front and rear of the building can probably be modified to raise windows. In a more modern townhouse it may be possible to abandon the lowest floor and make adjustments/repurpose the upper floors.

Regardless of the type of construction, if a row house was Substantially Damaged the requirements for areas below the BFE must be followed in order to have the lowest floor above the BFE considered the building’s lowest floor. Modification options for row homes in areas subject to high velocity wave action (Zone V) may be limited.

Rowhouse mitigation illustration

 

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WIND

Q1. How can I protect the roof of my home from water intrusion?

A1. Installation of a secondary water barrier (SWB) over the structural wood panel sheathing can help prevent water intrusion, even when shingles are blown off of the roof. The SWB should be applied after the roof deck has been adequately strengthened and before a new roof covering is installed. Technical Fact Sheet No. 7.2 in FEMA P-499, Home Builder’s Guide to Coastal Construction (FEMA 2010a), provides guidance on how to install a SWB beneath asphalt shingle roof coverings. Although not specifically addressed, builders can also use Technical Fact Sheet No. 7.2 as guidance on installing SWBs over wood board decking.

Section 4.1.1.2 of FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010b), offers several alternatives to installing underlayments for shingle roofs, metal roofs, and concrete and tile roofs. FEMA P-804 also discusses installing new roof coverings (Section 4.1.1.3). Proper installation of roof coverings is necessary to avoid their being ripped from the home during a high-wind event.

Additional guidance for optimizing roof performance can be found in Technical Fact Sheets No. 7.1 through 7.6 in FEMA P-499 and in Section 12.7.5 of FEMA P-55, Coastal Construction Manual (FEMA 2011).

The use of spray polyurethane foam (SPF) adhesive is another option. As described in Section 4.1.2 of FEMA P-804, SPF adhesive can be applied to the underside of a roof deck at the joints between the roof sheathing panels and along all intersections between the roof deck and framing members. The application of SPF in this case serves two purposes: the connection between the roof deck and supporting structural members is enhanced, and the SPF seals the joints of the roof deck to prevent water intrusion. SPF is not, however, as effective as installing an underlayment, but may be considered when not replacing the entire roof covering.

As always, the manufacturer’s instructions should take precedence oversupersede all recommendations given in FEMA publications.

References:

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..

FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.

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Q2. How can the wind and water resistance of roof soffits in homes be improved?

A2. 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.

References:

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.

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Q3. Are there any wind-related building code requirements or design standards pertaining to the attachment of rooftop equipment?

A3. 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.

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 Q4. Does FEMA have any publications that address design and construction guidance for high wind?

A4. FEMA has several publications that address high-wind hazards. The following publications are useful references on residential construction in high-wind areas:

  • FEMA P-320 . Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business. Washington, DC. August 2008.
  • FEMA P-550. Recommended Residential Construction for Coastal Areas: Building on Strong and Safe Foundations. Washington DC. December 2009.
  • FEMA P-499. Home Builder’s Guide to Coastal Construction: Technical Fact Sheet Series. Washington, DC. December 2010.
  • FEMA P-804. Wind Retrofit Guide for Residential Buildings. Washington, DC. December 2010.
  • FEMA P-55. Coastal Construction Manual. Washington, DC. August 2011.

FEMA also has many publications that address the high-wind hazard for non-residential construction:

  • FEMA P-424. Design Guide for School Safety in Earthquakes, Floods, and High Winds. Washington, DC. December 2010.
  • FEMA 543. Design Guide for Improving Critical Facility Safety from Flooding and High Winds: Providing Protection to People and Buildings. Washington, DC. January 2007.
  • FEMA 577. Design Guide for Improving Hospital Safety in Earthquakes, Floods and High Winds: Providing Protection to People and Buildings. Washington, DC. June 2007.
  • FEMA P-361. Design and Construction Guidance for Community Safe Rooms. Washington, DC. August 2008.

Other resources include:

  • ASCE 7. Minimum Design Loads for Buildings and Other Structures. American Society of Civil Engineers (ASCE) 2010.
  • ICC 600. Standard for Residential Construction in High Wind Regions. International Code Council (ICC) 2008.
  • ICC 500. Standard for the Design and Construction of Storm Shelters. International Code Council (ICC) 2008.
  • American Wood Council. Wood Frame Construction Manual Guide to Wood Construction in High Wind Areas for One- and Two-Family Dwellings (Exposure B versions for 90 mph, 100 mph, 110 mph, 120 mph, and 130 mph). 2006.

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FEMA SUBSTANTIAL DAMAGE ESTIMATOR (SDE) TOOL

Q1. Why do I need to determine substantial damage or substantial improvement for structures located in the Special Flood Hazard Area (SFHA)?

A1. Communities that participate in the National Flood Insurance Program (NFIP) are required to determine whether damage of any origin meets the criteria for substantial damage when the damage is to a structure in a mapped 100‑year floodplain. Similarly, improvements to structures in a mapped 100-year floodplain must be evaluated to determine whether the improvements meet the criteria for substantial improvement. Improvements include rehabilitation, remodeling, and lateral or vertical additions. Check with the local jurisdiction on additional requirements for substantial damage and substantial improvement requirements.

References:

FEMA P‑758, Substantial Improvement/Substantial Damage Desk Reference (2010).

FEMA NFIP Policy Index (2011).

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Q2. Can the FEMA SDE Tool be used to evaluate both substantial damage and substantial improvement?

A2. Yes. FEMA developed the SDE Tool to help NFIP participants meet their obligation to evaluate damage or improvements before approving permits for rehabilitation, remodeling, or lateral or vertical additions. Although FEMA’s guidance on the SDE Tool is geared toward damage (as the name suggests), the tool can be used to evaluate improvements by substituting the cost of the improvements for the cost of repairs.

References:

FEMA P-784 , Substantial Damage Estimator (SDE) User’s Manual and Workbook (2010).

FEMA NFIP Policy Index (2011).

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Q3. Am I required to use the SDE Tool when determining whether damage is substantial?

A3. 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, Substantial Improvement/Substantial Damage Desk Reference (2010).
  • FEMA 213, Answers to Questions about Substantially Damaged Buildings (1991).

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Q4. What resources are available from FEMA regarding substantial damage and substantial improvement?

A4. In addition to the SDE Tool, FEMA has developed the following:

  • FEMA P-784 , Substantial Damage Estimator (SDE) User’s Manual and Workbook (2010).
  • FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference (2010).
  • FEMA 213, Answers to Questions about Substantially Damaged Buildings (1991).

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Q5. What is the current version of the SDE Tool and the User Manual?

A5. The current version of the SDE Tool is SDE Version 1.1 (released August 2011).

The current version of the SDE User Manual and Workbook is FEMA P-784, Substantial Damage Estimator (SDE) User’s Manual and Workbook (2010). The user manual for Version 1.1 is the same as the user manual for the previous version of the tool.

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Q6. Why do I need administrative rights to install the SDE Tool on my computer?

A6. The requirement of administrative rights for installing the SDE Tool is set by the agency, community, or other entity that is responsible for the security and maintenance of the user’s computer. In addition, if the user does not have full-time administrative rights, the user must install the application in a folder where local write privileges are granted. For Windows XP, this folder is usually the “My Documents” folder. For other operating systems, see page 3-3 of the SDE User’s Manual.

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Q7. Can I install the SDE Tool in Windows 7?

A7. Yes. The SDE Tool was developed to operate in earlier versions of MS Windows, but the tool can be installed on computers running Windows 7. However, the tool cannot be installed in the location that is listed in the user manual for Windows XP. For more information, see page 3-3 of the user manual.

Note to Windows Vista and Windows 7 users: Replace the default installation path with C:\Users\<user name>\Substantial Damage Estimator 1.0, where <user name> is your user name on the computer.

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Q8. How should I address the following SDE error message, which cites duplicate records?

A8. The error message reads: “The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again.”

User’s can address this error message by exiting the SDE Tool and then re-opening it.

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Q9. What causes a “GDI+” or “Out of Memory” error when generating reports from the SDE Tool?

A9. GDI+ and Out of Memory errors can be caused by duplicate photo file names, the inclusion of special characters in the photo file name, or photos that are too large (i.e., photos that exceed the pixel limit). Before attaching photos, users should verify the following:

  • Every photo file name is unique
  • Photo file names do not include special characters such as #, $, %, and *
  • Each photo does not exceed 640x480 pixels or 3 MB

References:

Page 3-31, FEMA P-784, Substantial Damage Estimator (SDE) User’s Manual and Workbook (2010).

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Last Updated: 
08/05/2014 - 09:58
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