ADU rules in Seattle, WA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Seattle adopted Ordinance 127211 (June 2025) to comply with HB 1337. Up to 2 ADUs allowed per lot by right in all residential zones (SMC 23.42.022). No owner-occupancy requirement. Max ADU size 1,000 sq ft. ADUs cannot be used as STRs. DADUs allowed up to 32 ft in most NR zones.
SMC 23.42.022 (effective June 30, 2025) consolidates all ADU standards. Two ADUs allowed in addition to primary unit on all lots with residential development. Configurations include detached, attached, or stacked flats. Max size: 1,000 sq ft. Height up to 32 ft for DADUs in NR zones. No owner-occupancy required. No impact fee mandate above 50% of primary unit fee. ADUs exempt from street improvement requirements. Unit lot subdivisions permitted when DADU present. ADUs cannot be rented as STRs (periods under 30 days).
Unpermitted ADU construction: SDCI stop-work order and penalties. Non-compliant ADU: notice of violation.
Seattle, WA
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Seattle, WA
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Side-by-side rule comparisons with other cities in King County.
See how other cities in King County handle adu rules.
See how Seattle's adu rules rules stack up against other locations.
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