King County, WA Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard required
- 3 feet above base flood elevation
- Applies to
- unincorporated King County only
- Nonresidential option
- dry floodproofing by certified engineer
- Critical facilities
- 500-yr elevation or BFE+3 ft, higher
Summary
Unincorporated King County requires new and substantially improved buildings in flood hazard areas to elevate the lowest floor to the flood protection elevation, which the code defines as three feet above the base FEMA flood elevation.
Flood protection elevation: an elevation that is three feet above the base flood elevation. ... New, substantially improved or converted residential buildings and flood mitigation home elevations shall meet the following standards: 1. Elevate the lowest floor, including basement, to or above the flood protection elevation;
Full Breakdown
King County's floodplain code (K.C.C. 21A.24.223-.272) sets a three-foot freeboard above base flood elevation as the county's own "flood protection elevation" standard, well above FEMA's one-foot minimum. New, substantially improved, or converted residential buildings in the zero-rise flood fringe must elevate the lowest floor, including any basement, to or above that elevation; nonresidential buildings must either elevate the same way or be dry floodproofed by a certified engineer. Critical facilities must clear the higher of the 500-year floodplain elevation or three feet above base flood elevation. This applies only to unincorporated county land. Seattle, Bellevue, Kent, Renton, Federal Way, Auburn, Redmond, Kirkland, Sammamish, Burien, Shoreline, Issaquah, and other incorporated cities enforce their own floodplain codes.
Violations & Fines
Building below the flood protection elevation without an approved variance blocks permit issuance and can be pursued as a K.C.C. Title 23 code violation, since the county must show the alteration occurred in a delineated flood hazard area to enforce compliance.
Frequently Asked Questions
Does this cover Seattle addresses?
Can I build below the flood protection elevation?
Sources & Official References
Other rules in King County
Compare King County to another location·View the Washington environmental rules overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.