What is HB 1337?
✓ Verified against code · August 19, 2026
HB 1337 is the 2023 Washington law that set a statewide floor for ADU rules in cities over 25,000 residents. It required those cities to allow two ADUs per residential lot, eliminate owner-occupancy requirements, cap size limits no lower than 1,000 sq ft, cap height limits no lower than 24 ft, and stop requiring parking near major transit stops, with compliance due June 30, 2025 for larger cities. It set a floor, not a ceiling: cities then adopted their own ordinances on top of it, some far more generous than the minimum the law required.
Citation: HB 1337
How current is this?
Washington’s ADU rules run under HB 1337 (2023). HB 1337 required every Washington city over 25,000 people to allow two ADUs per residential lot, drop owner-occupancy requirements, cap size limits no lower than 1,000 sq ft, cap height limits no lower than 24 ft, and stop requiring parking near major transit — with compliance due June 30, 2025 for larger cities. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Washington ADU questions
- How many ADUs can I build in Washington?
- Do I need parking for an ADU in Washington?
- Can cities require me to live on the property?
- How big can an ADU be in Washington?
- Can I sell an ADU separately in Washington?
- Which WA cities have pre-approved ADU plans?
- When did WA ADU rules change?
- How tall can an ADU be in Washington?
- How close to my property line can an ADU be built?
- Will I have to pay impact fees on an ADU in Washington?
- How long does it take to get an ADU permit in Washington?
Not legal advice — local ordinances can go further than the state floor. The citation above points at the governing statute; check your city’s code for the specifics.