How tall can an ADU be in Washington?
✓ Verified against code · August 19, 2026
The state floor is 24 ft, set by HB 1337, and cities cannot set a lower cap for ADUs. Most cities in our data land right at that floor: Bellevue, Kent, Olympia, and Sammamish all cap detached ADUs at 24 ft. Some go higher — Bothell allows 30 ft (33 ft above an accessory structure), and Redmond lets ADU structures reach the underlying zone maximum, 38 ft in its base residential zone. A few cities have unresolved conflicts: Everett's and Burien's codes contain formulas that could compute below 24 ft on some lots, a tension with the state floor neither city has resolved.
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?
- What is HB 1337?
- 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 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.