Snohomish County, WA Environmental Rules: Flood Zones (2026)

SCC 30.65.030 expressly adopts the NFIP minimum floodplain management standards, making the chapter a prerequisite for the county's continued NFIP eligibility. SFHAs are mapped on the Snohomish County FIS dated June 19, 2020 and the corresponding FIRMs - they include floodways, density fringe areas, and Zone A/AE/AO/V areas along the Stillaguamish (between the mouth and approximately river mile 11.1, per Corps of Engineers study E-2-10-138 as modified by the county), the Snohomish River, the Skykomish/Snoqualmie tributaries, and Puget Sound coastal V zones. SCC 30.65.110 (general floodproofing) and 30.65.120 (specific floodproofing) require new and substantially improved residential structures in AE/A zones to have the lowest floor (including basement) elevated to or above the base flood elevation (BFE) plus county freeboard, with non-residential structures elevated or dry-floodproofed to that level. SCC 30.65.240 governs the density fringe area, restricting cumulative increases in BFE to no more than one foot to protect agricultural use of prime farmland in floodplains. New residential development is prohibited in the regulatory floodway under SCC 30.65, and no development may cause any rise in BFE in the floodway. SCC 30.50.412 ties Residential Code permit submittals to the flood hazard provisions. Snohomish County is also a Shoreline Management Act jurisdiction under RCW 90.58 - shorelines of statewide significance include Puget Sound and major rivers, and a Shoreline Substantial Development Permit is required for most development within 200 feet of the ordinary high water mark, in addition to floodplain compliance. FEMA-required elevation certificates, floodplain development permits, and substantial-damage/substantial-improvement determinations are issued by Snohomish County PDS Floodplain Management.