B.6. Floodproofing

Floodproofing is defined as any combination of structural or non-structural adjustments, changes or actions that reduce or eliminate flood damage to a building, contents and attendant utilities and equipment.^[451] Floodproofing can prevent damage to existing buildings and can be used to meet compliance requirements for non-residential buildings.

Dry floodproofing measures are either passive or active, depending on whether they require human intervention. Passive measures do not require human intervention and are recommended whenever possible. Active (or emergency) measures require human intervention and are effective only if there is enough warning time to mobilize the labor and equipment necessary to implement them and to safely evacuate.

The NFIP allows a new or substantially improved non-residential building in Zone A (A, AE, A1-30, AR, AO or AH) to have a lowest floor below the Base Flood Elevation, provided that a licensed professional engineer or architect has certified the design and methods of construction as being dry floodproofed in accordance with established criteria.

In addition, the NFIP allows for the use of wet floodproofing of structures with a lowest floor below the Base Flood Elevation, if allowed by permit in the local regulations or the local jurisdiction issues a variance and other requirements are met. Refer to FEMA Policy #104-008-03, Floodplain Management Requirements for Agricultural Structures and Accessory Structures, FEMA Floodplain Management Bulletin P-2140, Floodplain Management Requirements for Agricultural Structures and Accessory Structures, FEMA Floodplain Management Bulletin P-467-2 – Historic Structures, and NFIP Technical Bulletin 7, Wet Floodproofing Requirements and Limitations for guidance on the use of wet floodproofing.

The following terms are important when considering floodproofing projects:

• Substantial damage is damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damage condition would equal or exceed 50% of the market value of the structure before the damage occurred.
• Substantial improvement is any repair, reconstruction, rehabilitation, addition or improvement of or to a building, the cost of which equals or exceeds 50% of the market value of the building before the improvement or repair is started (certain historic structures may be excluded).
• Substantially impermeable walls shall not permit the accumulation of more than 4 inches of water depth during a 24-hour period, and sump pumps shall be required to control this seepage.
• Base Flood Elevation is the elevation of the base flood relative to the datum specified on a community’s FIRM. The base flood has a 1% chance of being equaled or exceeded in any given year (commonly called the 1% annual chance flood). Base flood elevations are shown on FIRMs for many SFHAs.
• Freeboard is an added margin of safety expressed in feet above a specific flood elevation, usually the Base Flood Elevation. In states and communities that require freeboard, buildings are required to be elevated or floodproofed to the higher elevation. For example, if a community adopts a 2-foot freeboard requirement, non-residential buildings are required to be elevated or floodproofed to 2 feet above the Base Flood Elevation.
• Design flood elevation is the elevation of the design flood relative to the datum specified on the community’s FIRM. The design flood is associated with the greater of the area subject to the base flood or the area designated as a flood hazard area on a community flood map or otherwise designated.

Many non-residential buildings can benefit from using a combination of wet and dry floodproofing measures for adequate protection. Combining these activities is particularly useful when one or more of the following building or site conditions exist:

• Multistory or split-level buildings where different measures can be applied to different foundation types at different elevations.
• Large factories, warehouses and other industrial facilities constructed of a variety of materials that respond better to multiple floodproofing measures.
• Groups of buildings on the same site but at different elevations.

More information on floodproofing can be found at the FEMA “Building Science – Flood Publications” webpage.

Dry floodproofing of non-residential structures consists of a combination of measures that result in a non-residential structure (including the attendant utilities and equipment) being watertight with all elements substantially impermeable to the entrance of floodwater and with structural components having the capacity to resist flood loads.

The purpose of dry floodproofing a building is to make it watertight to floods. Dry floodproofing reduces the potential for flood damage by reducing the probability that the building interior will be inundated. It can be an appropriate alternative for flood mitigation when relocating or elevating buildings is not cost-effective or technically feasible.

The minimum performance requirement for dry floodproofing measures is for a space that is protected by walls that are substantially impermeable and resistant to flood loads. A substantially impermeable wall limits water accumulation to a maximum accumulation of four inches in a 24-hour period with a sump pump to control seepage. However, the minimum performance requirement can be exceeded with proper planning, design and materials.

Incorporating flood damage-resistant materials into the dry floodproofing design up to the height of the dry floodproofing measure is recommended. Additionally, building systems such as walls and foundations may need to be strengthened to withstand direct flood forces and the loads imposed by floodproofing measures (e.g., shields, watertight doors), which are used to temporarily seal openings.

An effective dry floodproofing retrofit should include the following:

• Detailed site evaluation.
• Detailed building evaluation.
• Careful evaluation of all the dry floodproofing measures, including a consideration of residual risk.
• Design by a qualified licensed professional engineer or architect.
• Verification/testing that the constructed systems provide the desired floodproofing effectiveness. All flood abatement equipment used for dry floodproofing projects should be tested to nationally adopted standards, such as American National Standards Institute/FM 2510.
• Floodproofing Certificate for Non-Residential Structures for the dry floodproofing design.
• A plan for deploying any active dry floodproofing measures that require human intervention.
• Sufficient warning time to deploy active dry floodproofing measures and vacate the building.
• Operations and maintenance plan.

Though HMA does not allow for dry floodproofing residential structures, the NFIP gives special consideration to the unique value of designated historic buildings and structures. Provided such structures retain their designations, communities do not have to require them to be brought into compliance if the structures will be substantially improved or have been substantially damaged. The NFIP definition of “historic structures” generally includes structures that are (1) listed or preliminarily determined to be eligible for listing in the National Register of Historic Places, (2) certified or preliminarily determined by the Secretary of the Interior Department as contributing to the historical significance of a registered historic district or a district preliminarily determined to qualify as a registered historic district, or (3) designated as a historic site under a state or local historic preservation program approved by the Secretary of the Interior Department.^[452] The definition does not include structures that are merely old, those that residents refer to as historic or those that happen to be located in historic districts.

When floodproofing measures are applied to historic structures (including historic residential structures), the measures should be designed to mitigate or reduce the flood risk while preserving the building’s historic integrity. Consultation with the state or tribal historic preservation officer and a design professional (engineer or architect), preferably experienced in rehabilitating historic structures, is necessary. Ideally, any floodproofing measure applied to a historic structure and/or its site will not affect the property’s designation. If a structure does not retain its historic designation, it is subject to the basic NFIP requirements for substantial improvement/damage.

Floodproofing measures for historic structures do not need to be comprehensive to provide at least some degree of protection.

Wet floodproofing consists of the use of flood-damage-resistant materials and construction techniques to minimize flood damage to areas below the flood protection level of a structure, which is intentionally allowed to flood.

Wet floodproofing involves the following:

• Using flood damage-resistant materials below the design flood elevation throughout the building.
• Raising utilities and important contents to or above the flood protection level.
• Installing and configuring electrical and mechanical systems to minimize disruptions and facilitate repairs.
• Installing flood openings or other methods to equalize the hydrostatic pressure exerted by floodwaters.
• Installing pumps to remove floodwater gradually from basement areas after the flood (pump systems are only permitted when NFIP compliance is not required).

For information on NFIP requirements for wet floodproofing, refer to 44 CFR § 60.3, NFIP Technical Bulletin 7, FEMA Policy #104-008-3 and Floodplain Management Bulletin P-2140.

Non-residential floodproofing projects are eligible under HMGP, HMGP Post Fire, BRIC and FMA.

Dry floodproofing projects are eligible for non-residential structures and historic residential structures outside of Coastal A Zones (areas within the SFHA with an inland limit of the Limit of Moderate Wave Action) or Coastal High Hazard Areas (Zone V, VE, or V or V1-30).

Wet floodproofing projects are eligible in areas below the lowest floor (i.e., in areas that will be used for parking, storage, or access).

Dry floodproofing is not permitted in Coastal A Zones (areas within the SFHA with an inland limit of the Limit of Moderate Wave Action) or Coastal High Hazard Areas (Zone V, VE, or V or V1-30).

Wet floodproofing of structures where the lowest floor is below the required elevation is ineligible. A general list of ineligible activities is included in Part 4.

Applicants and subapplicants must demonstrate that mitigation projects are cost-effective. Projects must be consistent with Part 5.

Determining the cost-effectiveness of a floodproofing project can be done using either the Flood Modeled Damage methodology or Historic/Professional Expected Damage methodologies, both of which are part of the FEMA BCA Toolkit. The Flood Modeled Damage method relies on flood hazard data, building characteristics and Depth-Damage Functions. The Historic/Professional Expected Damage methodology relies on historical or expected damage along with a recurrence interval associated with the damage. The Historic/Professional Expected Damage methodology is used more often for floodproofing because it generally requires less data collection and may better represent the complexity of some floodproofing projects.

For dry floodproofing, retrofitting an entire large building or multiple buildings is a complex and expensive undertaking that requires analysis and design to protect the buildings against flooding from numerous points of entry of various sizes. Consequently, limiting dry floodproofing measures to the most critical elements or operations of a facility that cannot be elevated may be more cost-effective. Building managers and owners can then focus on elevating other critical areas and wet floodproofing other lower-level areas that are less critical. This situation may apply to flood-prone hospitals, schools, fire and police stations, emergency operations centers, communication and data centers, essential government buildings and other critical facilities that serve the community or affect the safety, health or welfare of a large population.

Table 25 highlights the cost-effectiveness of floodproofing projects.

Table 25: Likelihood of Cost-Effectiveness of Floodproofing Project

Magnitude of Potential Loss ($)	Low Probability	Medium Probability	High Probability
Low	Unlikely	Unlikely	Likely
Medium	Unlikely	Likely	Highly Likely
High	Likely	Likely	Highly Likely

For more information, refer to Part 5.

Projects must be consistent with Part 3. Mitigation projects assisted by HMA must be both feasible and effective at mitigating the risks of the hazard(s) for which the project was designed. A project’s feasibility is demonstrated through conformance with accepted engineering practices, established codes, standards, modeling techniques or best practices. FEMA recommends assessing a building in two stages. First, a preliminary assessment is completed to help determine the overall feasibility of flood mitigation. The preliminary assessment is often based only on a visual examination of the building and, when available, a review of construction drawings. The desired flood protection level of dry floodproofing can also be determined in the preliminary assessment.

If the preliminary assessment suggests that flood mitigation is possible, the next stage is to perform additional site and drawing reviews and conduct testing and analyses to confirm that flood mitigation is feasible. A detailed assessment requires accurate drawings of the building or, if drawings are not available, invasive testing to determine the structural aspects and condition of the building. Soil tests to determine the type and permeability of on-site soils may also be needed.

The condition assessment must not only determine the ability of structural components to withstand flood loads but also their impermeability. For example, basement walls between adjacent buildings should be evaluated for flood load resistance and impermeability. This is especially important in an urban environment or buildings constructed in phases; otherwise, the source of flooding may become the adjacent building. Structural components, window wells, ventilation openings and utilities can each be floodwater points of entry if not properly assessed and mitigated. During the condition assessment, bowing, lateral movement, corrosion, staining and evidence of frequent water entry all may indicate the building is not an ideal candidate for dry floodproofing.

A structural engineer can evaluate the building to determine whether it is feasible to retrofit by computing flood loads, evaluating options, developing a dry floodproofing solution and preparing a probable budget. For additional guidance refer to FEMA P-936, Floodproofing Non-Residential Buildings and NFIP Technical Bulletin 3, Requirements for the Design and Certification of Dry Floodproofed Non-Residential and Mixed-Use Buildings. Because the final design may not be completed prior to award, once the project is awarded, the design must be finalized by a licensed professional engineer or architect, with some exceptions.

FEMA will use the latest published edition of ASCE 24 or its equivalent as the minimum design criteria for all HMA-assisted floodproofing projects in flood hazard areas. These flood hazard areas include floodways, coastal high-hazard areas and other high-risk flood hazard areas such as alluvial fans, flash flood areas, mudslide areas, erosion-prone areas and high-velocity areas. ASCE 24 addresses design and construction requirements for floodproofing for buildings in flood hazard areas when used for the construction of new buildings or to substantially improve existing buildings (including repair of substantial damage). ASCE 24 sets forth requirements for elevation, foundation designs, enclosures below elevated buildings, materials, wet and dry floodproofing, utility installations, building access and miscellaneous structures (e.g., decks, porches, patios, garages, chimneys and fireplaces, pools, and above- and belowground storage tanks). The use of the ASCE 24 standard or its equivalent will allow applicants to better demonstrate the technical feasibility and effectiveness of HMA projects in flood hazard areas and facilitate consistency in implementing HMA projects in flood hazard areas.

In addition, all HMA-assisted floodproofing projects in flood hazard areas must also comply with the requirements established by the Federal Flood Risk Management Standard. Refer to Part 4.I for more information about these requirements.

All subapplications submitted to FEMA must meet the EHP criteria in Part 4. All subapplications must provide the information described in Part 6 so that FEMA may perform the EHP review.

Mitigation projects sited within the SFHA are eligible only if the jurisdiction is participating in the NFIP. For FMA only, all properties included in a subapplication must be NFIP-insured at the time of the opening of the application period. The flood insurance policy must be maintained throughout the period of performance and for the life of the structure. For additional information on flood insurance requirements, refer to Part 4.J.

NFIP regulations do not permit wet floodproofing to be used to bring a substantial improvement/damage structure into compliance unless the area to be wet floodproofed is used solely for parking, building access or storage.^[453]

Application of wet floodproofing as a flood protection technique under the NFIP is limited to specific situations in Zone A (A, AE, A1-30, AH, AO and AR). For certain uses and types of structures, communities may allow wet floodproofing only through the issuance of a variance from certain floodplain management requirements. The situations and conditions in which a community may allow wet floodproofing are described in detail in NFIP Technical Bulletin 7, Wet Floodproofing Requirements and Limitations for Buildings and Structures Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program (May 2022).

For structures in Zone V (V, VE and V1-30), more stringent design and construction requirements have been established for the portion of the structure below the Base Flood Elevation. For information on V-zone design and construction requirements, refer to the NFIP regulations under 44 CFR § 60.3; FEMA P-55, Coastal Construction Manual: Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas, Fourth Edition, Volume I (Aug. 2011); and the FEMA “National Flood Insurance Technical Bulletins” webpage. For more information on NFIP's general requirements for wet floodproofing, refer to 44 CFR § 60.3, NFIP Technical Bulletin 7, FEMA Policy #104-008-3 and Floodplain Management Bulletin P-2140.

An important objective of the NFIP is to protect structures constructed in floodplains from flood-induced damage. In support of this objective, the NFIP regulations include building design and construction criteria that apply to new construction and substantial improvements (including structures that have incurred substantial damage) of existing structures in SFHAs. Residential structures in Zone A (A, AE, A1-30, AR, AO or AH) must be constructed with their lowest floors elevated to or above the Base Flood Elevation. Non-residential structures constructed in Zone A (A, AE, A1-30, AR, AO or AH) must either have their lowest floors elevated to or above the Base Flood Elevation or be dry floodproofed to or above the Base Flood Elevation. Measures to accomplish dry floodproofing of non-residential structures must provide watertight protection and be designed to withstand hydrostatic, hydrodynamic and impact forces produced by flooding. The intent is to provide complete protection at least up to the floodproofing design level, which must, at a minimum, be at the Base Flood Elevation.

Dry floodproofing can be used to fulfill the requirements for non-residential buildings in SFHAs that are not subject to high-velocity wave action. Some requirements apply to existing buildings when the cost of repairing or improving a building in an SFHA equals or exceeds 50% of the building’s market value. NFIP requires new and substantially improved buildings be constructed in ways that minimize or prevent flood damage. As with new non-residential buildings, existing non-residential buildings may be brought into compliance by elevating them on compliant foundations or, if determined to be feasible, by implementing dry floodproofing measures. For more information on NFIP's general requirements for dry floodproofing, refer to 44 CFR § 60.3(c) and NFIP Technical Bulletin 3.^[454]

Floodproofing Certificate for Non-Residential Structures (FEMA Form 086-0-34) is required for floodproofing measures to be recognized for NFIP purposes. It is used by the designer to certify the design, correct construction/installation of dry floodproofing components, and confirm existence of a comprehensive Maintenance Plan. It is required for the following types of buildings in Zone A for dry floodproofing:

• Dry floodproofed non-residential structures (no residential uses).
• Dry floodproofed portions of mixed-use buildings that have all residential uses located above the dry floodproofing design elevation.

This certificate is not required for wet floodproofing.

For structures in the SFHA at the completion of the project and all structures receiving FMA regardless of location in the SFHA, flood insurance must be maintained for the life of the property.^[455] For more information, refer to Part 4.J.

All subapplications submitted to FEMA must meet the eligibility criteria in Part 4. All subapplications must have a scoping narrative in accordance with Part 6. Project-specific criteria are highlighted below.

FEMA may request additional information after the subapplication has been submitted to ensure all necessary information is received. However, all information required by the regulations and the HMA Guide must be received before an assistance decision and award or final approval can be made.

Businesses cannot apply for HMA programs, so the non-residential property owner must work with the local government to develop a project subapplication on behalf of the owner. Local governments may submit a retrofit project for a property as an individual subapplication or combine it with other projects as part of an aggregate subapplication (subject to program restrictions). Aggregating benefit and cost values is allowed for multiple buildings if they are all vulnerable to damage from similar hazard conditions. Refer to Part 5 for information on aggregating projects in one subapplication.

For non-residential floodproofing projects, the subapplication must include the following:

• Identification of the property to be mitigated.
• Identification of key project personnel and roles, such as design professional and contractor.
• Selection of an eligible project.
• Inspection of the building by a licensed professional engineer or architect to verify the project can be implemented, if possible; if not done at this stage, it must be done during Step 4, Perform a Condition Assessment (Existing Structures).^[456].
• Development of a project budget and work schedule.
• Completion of BCA using the FEMA BCA Toolkit (refer to Part 5 for additional information); if the BCR is 1.0 or more, the project is cost-effective. FEMA requires a BCR of 1.0 or greater for HMA.
• Verification that properties in designated SFHAs will obtain flood insurance and that the insurance will be recorded on the property deed.

The local government submits the subapplication to the state. The state then selects projects based on its priorities and submits applications to FEMA for review. FEMA reviews the projects for eligibility, completeness, engineering feasibility, cost-effectiveness, cost-reasonableness and EHP documentation. The review process also confirms all hazard mitigation activities adhere to all relevant statutes; regulations; program requirements, including other applicable federal, state, local and tribal laws; implementing regulations; and executive orders, all of which are detailed in the program guidance. Once FEMA approves a project and awards the grant, the state distributes the assistance to the local government, which distributes it to individuals as appropriate. Construction activities must not begin until after the money has been awarded; HMA is not available for activities initiated or completed prior to award or final approval.

All subapplications, as part of the scope of work, must include an activities description referencing industry standards or project plans and specifications.

Additionally, a scope of work must include work activities, deliverables and timelines associated with a project. For a dry floodproofing project, the scope of work typically includes the problem description, proposed solution, description of existing conditions and work schedule.

All subapplications must include a line-item breakdown of all anticipated costs. Project costs typically include:

• Labor.
• Materials.
• Engineering and design.
• Project management.
• Construction engineering and inspection.
• Permitting.
• Estimated annual maintenance costs.

The costs for dry floodproofing a structure will depend on the following factors:

• Size of the structure.
• Height of the flood protection elevation.
• Types of sealant and shield material used.
• Number of plumbing lines that must be protected by check valves.
• Number of openings that must be covered by shields.

Subapplicants may apply for subrecipient management costs to cover administrative costs. Management costs must be included in the subapplication budget as a separate line item. More information about the requirements for management cost requests can be found in Part 13.

The following are basic steps in implementing an approved HMA non-residential floodproofing project:

1. If a design was not developed before application development, secure a licensed professional engineer or architect to design, inspect and sign off on a mitigation retrofit solution within the bounds of the approved subaward.
2. If a design solution was developed before application development or if a licensed professional engineer or architect is not needed because of the nature of the work, secure the services of a contractor to execute the work in the approved subaward.
3. Monitor the work being performed to ensure that all award and subaward requirements are being met.
4. Inspect the finished project and verify that all award and subaward requirements have been met. Work with the designer/contractor to resolve any issues of concern and work with the state in closing out the subaward after all requirements have been met.

Recipients are required to report deviations from budget, project scope or objectives, in accordance with Part 8. Recipients must request prior approvals from FEMA for budget and program plan revisions.^[457]

If the final design is not complete prior to award, once the project is awarded, the design must be finalized by a licensed design professional, with some exceptions. Any changes to the scope of work or budget because of completing the final design or to address permitting requirements must be consistent with Part 8. Construction design activities are defined as construction activities; therefore, budget changes involving them must be consistent with Part 8.F.2.

Recipients and subrecipients must closeout projects in a timely manner consistent with Part 9.

When the project has been completed, a licensed professional engineer or architect (preferably the same one as used during the initial project design) must conduct a final inspection and verify in an inspection report that the project they designed/signed off on was implemented as intended in the approved subaward. If a contractor was the only professional who performed the work, the contractor should verify in writing that they performed the work as outlined in the contract and subaward. The subrecipient must ensure that the subaward requirements have been met through any contracts the subrecipient has with professional engineers and architects or contractors because the subrecipient is ultimately responsible for meeting the requirements. Poorly written contracts can result in work that complies with the contract but is non-compliant with the subaward requirements. The written verification of the work performed along with other project documentation demonstrating subaward compliance will help facilitate a smooth, efficient project closeout.

After obtaining project verification from the designer/contractor, the subrecipient then submits the subaward project documentation to the recipient. The recipient verifies that the work was completed in accordance with the approved subaward documentation, including the scope of work, and performs the closeout procedures.

In addition to the typical HMA program closeout processes, closeout of non-residential floodproofing projects generally includes the following:

• A certificate of occupancy and the final Elevation Certificate (FEMA Form 086-0-33) and Floodproofing Certificate for Non-Residential Structures (FEMA Form 086-0-34) for each structure in the project to certify that the structure is code compliant and was elevated or floodproofed to the required elevation. FEMA will use the latest published edition of ASCE 24 or its equivalent as the minimum design.
• A copy of a recorded deed for each property, including deed requirements for property maintenance and flood insurance.
• A signed Acknowledgement of Conditions for Properties Using FEMA Hazard Mitigation Assistance form for each structure.
• A certification from a building official or licensed professional engineer or architect verifying the structure was designed and constructed to the minimum standard of the two most recently published editions of the International Codes, even in locations where no code has been adopted.
• Final inspection report with the name of the inspector and date of inspection.
  • The report must provide a narrative of all the components of the project that were completed and verify the scope of work was completed and is consistent with activities identified in the scope of work.
  • The report must include photographs of the project area(s) with clear labels and a map of the project area(s) with accurate geospatial coordinates.
• A front, rear and side photograph of the final structure, including the date of the photograph, property address, latitude/longitude to the nearest sixth decimal place and the name of the photographer.
• Verification of flood insurance for each structure.
• An update to the property site information in the FEMA electronic application system for each structure.