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: August 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	Not allowed

No floodproofing of any kind, dry or wet, is permitted in V zones. Below-BFE enclosures there are instead governed by 44 CFR 60.3(e)'s breakaway wall requirements - a structural rule about how the enclosure must collapse under wave forces, not a floodproofing method. Dry floodproofing is also 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.

Frequently Asked Questions

What is the difference between dry and wet floodproofing?

Dry floodproofing keeps floodwater completely out of the building by sealing the walls and installing flood shields over openings. Wet floodproofing allows water to enter the lower areas in a controlled way while using flood-resistant materials and relocating damageable items above the Base Flood Elevation. Dry floodproofing is only allowed for non-residential and mixed-use buildings in A zones.

Can I floodproof my home instead of elevating it?

No. Under NFIP rules, residential buildings in the SFHA must be elevated to or above the Base Flood Elevation. Dry floodproofing as an alternative to elevation is only permitted for non-residential and mixed-use buildings in A zones. Residential property owners will not receive insurance premium credits for floodproofing measures.

What is a Floodproofing Certificate?

The Dry Floodproofing Certificate (FEMA Form FF-206-FY-22-153) is the official form used to document that a non-residential building has been designed and constructed to be dry floodproofed in compliance with NFIP requirements. It must be signed by a registered professional engineer or architect and is used by insurance agents to rate the policy at a lower premium.