Floodproofing: Dry vs. Wet
Floodproofing can protect a building from flood damage without raising it above the Base Flood Elevation, but NFIP rules limit who can use it, where, and how.
Last updated: February 2026
What Is Floodproofing?
Floodproofing is the process of making a building resistant to flood damage without elevating the entire structure above the Base Flood Elevation (BFE). The NFIP recognizes two distinct approaches - dry floodproofing and wet floodproofing - each with different rules about where they can be used and which types of buildings qualify.
Floodproofing is not allowed as a substitute for elevation on residential buildings in any flood zone. Homes, apartments, and condominiums in the SFHA must be elevated. Only non-residential and mixed-use buildings in A zones may use dry floodproofing as an alternative.
Dry vs. Wet Floodproofing
Dry Floodproofing
Keeps floodwater completely out. The building envelope is sealed below the flood protection level using waterproof coatings, impermeable wall construction, and flood shields or closures over all openings. The structure must also resist hydrostatic pressure, buoyancy, and debris impact.
- ✓Non-residential and mixed-use buildings in A zones
- ✗Residential buildings (any zone)
- ✗Any building in V zones (wave action)
Wet Floodproofing
Allows floodwater to enter lower areas in a controlled way. Equalizes pressure on walls to reduce structural loads. All materials below the BFE must be flood damage-resistant, and mechanical/electrical systems must be elevated or waterproofed.
- ✓Enclosures below elevated buildings (residential and non-residential)
- ✓Below-grade parking, crawlspaces, service areas
- !Requires flood openings (vents) for water equalization
Where Is Floodproofing Allowed?
| Scenario | Dry Floodproofing | Wet Floodproofing |
|---|---|---|
| Non-residential in A zones | Allowed (alternative to elevation) | Allowed |
| Residential in A zones | Not allowed | Enclosures below elevated structure only |
| Any building in V zones | Not allowed | Breakaway walls only (no sealed enclosures) |
Dry floodproofing is generally not recommended for depths greater than 3 feet above adjacent grade because hydrostatic pressure against walls becomes extreme. The design must protect to at least the BFE, and FEMA recommends designing to BFE plus freeboard.
The Floodproofing Certificate
The Dry Floodproofing Certificate (FEMA Form FF-206-FY-22-153) is the official form that documents and certifies a non-residential building has been dry floodproofed in compliance with NFIP requirements. Think of it as the floodproofing equivalent of the Elevation Certificate.
When is it required?
When a non-residential building in an SFHA has been dry floodproofed instead of elevated, and the owner wants insurance premium credits or the community needs to verify floodplain ordinance compliance.
Who signs it?
A registered professional engineer or architect who certifies the design, materials, structural adequacy, and maintenance plan for flood shields and closures.
How does it affect insurance?
Insurance agents use the certified protection level to rate the policy. The higher the protection level relative to the BFE, the lower the premium. Without a certificate, the building is rated as if it has no flood protection.
FEMA P-936 ("Floodproofing Non-Residential Buildings") provides the detailed design guidance that engineers and architects follow when designing dry floodproofing systems. The certificate documents that the as-built conditions meet those standards.
Flood Damage-Resistant Materials
Whether a building is elevated, dry floodproofed, or wet floodproofed, any materials used below the BFE must be flood damage-resistant. FEMA Technical Bulletin 2 classifies building materials into five classes. Only Class 4 and 5 materials are acceptable below the BFE.
| Class | OK Below BFE? | Examples |
|---|---|---|
| 5 | Yes | Concrete, steel, ceramic tile, pressure-treated lumber |
| 4 | Yes | Some engineered wood with waterproof adhesives, vinyl |
| 3 | No | Some treated wood (clean water only) |
| 2 | No | Standard drywall, fiberglass insulation |
| 1 | No | Paper, carpet padding, particleboard |
The standard is based on materials being able to withstand contact with floodwaters for at least 72 hours and then be cleaned and returned to a serviceable condition. Standard gypsum wallboard and fiberglass batt insulation (both Class 2) are among the most commonly used materials that fail this requirement.
Related Resources
How BFE determines the floodproofing protection level.
The companion form for elevated buildings.
What a Special Flood Hazard Area means for your property.
Why floodproofing is not allowed in V zones.
How floodproofing certification can reduce your premium.
Development restrictions in the regulatory floodway.
The 50% rule that may require full compliance when floodproofing.
Sources
This page summarizes information from FEMA and other official resources in plain language. For full technical details, see the links below.
- FEMA P-936 — Floodproofing Non-Residential BuildingsDirect Source
Detailed FEMA guidance on dry and wet floodproofing design. Hosted by WBDG. If removed, search wbdg.org for "FEMA P-936".
ASFPM announcement on updated Floodproofing Certificate form. If removed, search floods.org for "dry floodproofing certificate".
- FEMA Flood Insurance OverviewGeneral Reference
Broad FEMA flood insurance hub. Covers floodproofing credit information under NFIP rating.
Sources last verified: February 2026
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