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Frequently Asked Questions About Building Science: Floods

Find answers to frequently asked questions regarding FEMA Building Science Flood guidance, or see our other Building Science FAQ collections.

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

Flood Guidance

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

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.

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

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.

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.

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 a list of materials compliant with the National Flood Insurance Program (NFIP) regulations for use below the base flood elevation?

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.

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.

References:

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

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.

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

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.

How is the net open area of a flood opening ("flood vent") measured?

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 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.

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

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.

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.

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.

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

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.

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

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.

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

The National Flood Insurance Program (NFIP) requires that the heating, ventilation, and air conditioning (HVAC) system in new construction or Substantial Improvement 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 new construction or Substantial Improvement 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, 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. 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.
  • FEMA. 2017.  Protecting Building Utility Systems from Flood Damage: Principles and Practices for the Design and Construction of Flood Resistant Building Utility Systems. FEMA P-348, Edition 2 Washington, DC, February 2017.
  • National Archives and Records Administration. 2017 44 Code of Federal Regulations Ch. 60.3(a) through (ef), “Flood plain management criteria for flood-prone areas.” Washington, DC. October 2017

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

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. 2017.  Protecting Building Utility Systems from Flood Damage: Principles and Practices for the Design and Construction of Flood Resistant Building Utility Systems. FEMA P-348, Edition 2 Washington, DC, February 2017.
  • FEMA. 2010. Home Builder’s Guide to Coastal Construction: Fact Sheet 8.3, Protecting Utilities. FEMA P-499. Washington, DC. December 2010.

I have a row house. How do I elevate it?

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.

Figure indicating the “before” and “after” of flood mitigation for a row house. The “after” includes fill in the lowest floor up to the grade level and the living area floors are moved to above the freeboard level.

Last updated September 17, 2020