Washington ADU Laws & Rules by City (2026)

Key Washington ADU Laws

HB 1337 (2023): Cities must allow at least 2 ADUs per lot
No owner-occupancy mandate; off-street parking can't be required within ½ mile of major transit (otherwise limited to 1-2 spaces by lot size) per RCW 36.70A.681
Impact fee limits for ADUs under certain sizes
Seattle and Tacoma have the most progressive local policies

Washington Cities ADU Comparison

City	Max Size	Setbacks	Permit Fees	Build Cost	1BR Rent	Score
Seattle	1,000 sq ft of floor area above grade (size also constrained by FAR and lot coverage)	5 feet	$2,000-$5,000+ in SDCI permit fees (varies with valuation; hourly review rates apply)	$160,000-$320,000	$1,600-$2,100/mo	9/10
Spokane	1,000 sq ft	Confirm with Spokane Planning (SMC Title 17C)	$2,000-$3,500	$110,000-$220,000	$1,000-$1,450/mo	6/10
Tacoma	1,000 sq ft living area	15 feet (no setback required from an alley)	$1,800-$2,800	$135,000-$270,000	$1,300-$1,750/mo	8/10
Vancouver	1,000 sq ft gross floor area	Confirm with Vancouver Planning (VMC 20.810.040)	$1,900-$3,200	$135,000-$270,000	$1,250-$1,700/mo	7/10

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