Franklin County, WA Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard, BFE known
- 1 foot above base flood elevation
- Freeboard, BFE unavailable
- 2 feet above highest adjacent grade
- Critical facilities
- 3 feet above base flood elevation
- Applies to
- New construction and substantial improvements
- Mechanical equipment
- Waterproofed or elevated 1 foot above BFE
- Governing section
- Franklin County Code § 15.08.250
Summary
New and substantially improved homes in Franklin County's mapped flood zones must sit at least one foot above base flood elevation where a BFE is set, or two feet above the highest adjacent grade where it isn't. Mechanical equipment must clear the same one-foot freeboard.
A.Residential Construction:1.In AE and A1-30 zones or other A zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated one foot or more above base flood elevation. Mechanical equipment and utilities shall be waterproof or elevated least one foot above the BFE.2.New construction and substantial improvement of any residential structure in an unnumbered A zone for which a BFE is not available and cannot be reasonably obtained shall be reasonably safe from flooding, but in all cases the lowest floor shall be at least two feet above the highest adjacent grade.
Full Breakdown
160. For residential construction in AE and A1-30 zones, or other A-zoned areas where the BFE can reasonably be determined, the lowest floor, including any basement, must be elevated one foot or more above the BFE, and mechanical equipment and utilities must be waterproofed or elevated at least one foot above the BFE as well. Where a property sits in an unnumbered A zone with no obtainable BFE, the lowest floor must instead be at least two feet above the highest adjacent grade. 250(B), with an alternative dry-floodproofing path certified by a registered engineer or architect.
Manufactured homes get an identical rule: the lowest floor must clear the BFE by one foot or more and be anchored to a permanent foundation. Critical facilities are held to a higher three-foot freeboard above BFE. Any fully enclosed space below the elevated lowest floor must have flood vents meeting minimum opening criteria and can only be used for parking, building access, or storage, never habitation. 260.
Violations & Fines
Constructing or substantially improving a residential or nonresidential structure below the elevation Section 15.08.250 requires breaches the conditions of the development permit issued under Chapter 15.08. Locating mechanical equipment below the required freeboard elevation can also drive up flood insurance premiums, and the floodplain administrator can deny or revoke a permit for noncompliant construction under the chapter's general enforcement authority.
Frequently Asked Questions
How high above the flood elevation does my house need to be in Franklin County?
Does the freeboard rule apply to manufactured homes?
Are commercial buildings held to the same elevation standard?
Sources & Official References
Other rules in Franklin County
Compare Franklin County to another location·View the Washington environmental rules overview
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