WA
Washington ADU Laws 2026
Primary statutes: HB 1337 (2023)
Washington's HB 1337 (2023) is one of the strongest ADU laws in the country, requiring cities of 25,000+ to allow at least two ADUs per lot in most residential zones.
At a glance
Max Detached
1000 sqft
Max Attached
1000 sqft
Max Height
24 ft
Min Setback
5 ft
Owner-occupancy
Not required
Long-term rentals
Allowed
Short-term rentals
Allowed
Permit decision
60 days
Parking required
Not required
Full summary
HB 1337 mandates that cities and counties planning under the Growth Management Act allow at least two ADUs per single-family lot in urban growth areas. Owner-occupancy requirements are prohibited. Off-street parking cannot be required for ADUs within half a mile of major transit.
Seattle has been a national leader in pre-approved DADU plans, dramatically reducing permit timelines and costs. Local jurisdictions had until June 30, 2025 to update their codes.