Washington ADU Laws & Rules (2026)

Compare ADU zoning rules across 4 Washington cities. Average ADU score: 7.5/10.

Very ADU-FriendlyHB 1337 (2023)

Key Washington ADU Laws

Key Washington ADU Laws

  • HB 1337 (2023): Cities must allow at least 2 ADUs per lot
  • No owner-occupancy or off-street parking mandates
  • Impact fee limits for ADUs under certain sizes
  • Seattle and Tacoma have the most progressive local policies

Washington Cities ADU Comparison

CityMax SizeSetbacksPermit FeesBuild Cost1BR RentScore
Seattle 1,200 sq ft 5 feet $1,800-$2,800 $160,000-$320,000 $1,600-$2,100/mo 9/10
Spokane 1,000 sq ft 15 feet $2,000-$3,500 $110,000-$220,000 $1,000-$1,450/mo 6/10
Tacoma 1,100 sq ft 10 feet $1,800-$2,800 $135,000-$270,000 $1,300-$1,750/mo 8/10
Vancouver 1,050 sq ft 10 feet $1,900-$3,200 $135,000-$270,000 $1,250-$1,700/mo 7/10

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