King County, WA Environmental Rules: Flood Zones (2026)
FEMA flood zone rules in King County, WA, also called floodplain regulations or special flood hazard area (SFHA) rules, determine flood insurance requirements and elevation standards for new construction.
Key Facts
- Permit required
- any new floodplain development
- Governing chapter
- K.C.C. 21A.24.223 through .272
- Elevation standard
- lowest floor above flood protection elevation
- Scope
- unincorporated county only, not Seattle
- Design certification
- structural or civil engineer required
Summary
Unincorporated King County requires a floodplain development permit before any new construction, fill, or substantial improvement begins in a mapped flood hazard area, per County Code Title 21A.24.
Before initiating any new floodplain development, the person proposing the development shall obtain a floodplain development permit from King County. Exceptions to other permit requirements do not apply to floodplain development. The applicant shall ensure that all necessary permits have been obtained from those federal, state or local government agencies from which prior approval is required. (Ord. 19128 § 27, 2020: Ord. 17539 § 54, 2013).
21A.24.272 Coastal high hazard areas - development standards - exceptions to flood hazard standards. Within coastal high hazard areas, which includes zone VE and adjacent zone AE areas on the Flood Insurance Rate Maps, the following applies:
A. All new, substantially improved or converted residential or nonresidential buildings shall be elevated on pilings and columns so that:
1. The bottom of the lowest horizontal structural member of the lowest floor, excluding the pilings or columns, is elevated to or above the flood protection elevation;
2. The pile or column foundation and building attached thereto is anchored to resist flotation, collapse and lateral movement due to the effects of wind and water loads acting simultaneously on all building components. Wind and water loading values shall each have a one percent chance of being equaled or exceeded in any given year; and
3. All building utilities are elevated to or above the flood protection elevation;
Full Breakdown
The permit requirement in K.C.C. 21A.24.271 applies to any new floodplain development in unincorporated King County: the zoning code that governs Seattle, Bellevue, Kent, Renton, Auburn and roughly 30 other incorporated cities does not reach this far; each enforces its own municipal floodplain rules. Once triggered, K.C.C. 21A.24.240 requires new and substantially improved residential buildings in the zero-rise flood fringe to elevate the lowest floor to or above the flood protection elevation, use flood-resistant materials, and avoid reducing the floodplain's base flood storage volume without providing compensatory storage. A structural or civil engineer must certify elevation and floodproofing designs before permits issue.
Violations & Fines
Building without a floodplain permit triggers a K.C.C. Title 23 code enforcement action; the County need only show by a preponderance of evidence that work occurred in the flood hazard area, per K.C.C. 21A.24.2705.
Frequently Asked Questions
Does this cover Seattle or Bellevue floodplains?
What triggers the floodplain development permit?
Sources & Official References
Other rules in King County
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