1 county-level rule, plus city-specific rules for 4 cities in Snohomish County, Washington.
Verified from official government sources
Snohomish County Code 30.28.010 governs accessory dwelling units (ADUs) in unincorporated Snohomish County and is being updated to comply with Washington's statewide ADU preemption under HB 1337 (2023), codified at RCW 36.70A.681, which requires counties planning under the Growth Management Act to allow up to two ADUs per single-family lot inside urban growth areas. Existing SCC 30.28.010 caps ADU floor area at 1,200 sq ft (excluding garages, porches, unheated storage, and unfinished basements), allows up to two ADUs on lots with a single-family principal unit, and reduces road setbacks to five feet on certain public roads.
4 cities in Snohomish County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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