Washington ADU
Law Guide 2026.
HB 1337 (2023) rewrote the rules for accessory dwelling units in every Washington city planning under the Growth Management Act. This guide translates the statute — RCW 36.70A.681 — into plain English and shows how each Puget Sound city has implemented it.
What HB 1337 actually requires
| Rule | Statute | What it means |
|---|---|---|
| Two ADUs per lot, by right | HB 1337 (2023) RCW 36.70A.681(1)(a) | Cities planning under GMA must allow at least two ADUs on any lot zoned for single-family use — any combination of detached, attached, or interior. |
| No owner-occupancy requirement | HB 1337 (2023) RCW 36.70A.681(1)(d) | Cities may not require the property owner to live in the primary house or the ADU. Investor-owned ADUs are explicitly permitted. |
| No off-street parking required within ½ mile of major transit | HB 1337 (2023) RCW 36.70A.681(1)(e) | If the lot is within a half-mile walking distance of a major transit stop, the city cannot require any new parking for the ADU. |
| Maximum size ≥ 1,000 sq ft | HB 1337 (2023) RCW 36.70A.681(1)(c) | Cities must allow ADUs up to at least 1,000 sq ft. Many Puget Sound cities allow 1,200 sq ft (Seattle DADUs) or larger. |
| Impact fees capped at 50% of single-family rate | HB 1337 (2023) RCW 36.70A.681(1)(g) | School, traffic, park, and fire impact fees on ADUs cannot exceed 50% of what's charged for a new single-family house. |
| ADUs may be sold separately as condominiums | HB 1337 (2023) RCW 36.70A.681(1)(h) | Cities must allow ADUs to be condominiumized and sold separately from the primary residence, opening fee-simple sale paths. |
| Same setbacks as primary structure | HB 1337 (2023) RCW 36.70A.681(1)(f) | Cities cannot impose larger setbacks on ADUs than they do on the primary house in the same zone. |
| Roof height ≥ 24 ft permitted | HB 1337 (2023) RCW 36.70A.681(1)(b) | Cities must allow ADU roof heights of at least 24 ft, enabling pitched roofs and modest second-story DADUs. |
How each Puget Sound city implements it
| City | Max size | Parking | Height | Notes |
|---|---|---|---|---|
| Seattle | 1,000 sq ft (DADU) | None required | 18–24 ft | Two ADUs per lot since 2019. SMC 23.44.041. |
| Bellevue | 1,000 sq ft | 1 stall, waived near transit | 24 ft | LUC 20.20.120 — owner occupancy removed 2024. |
| Tacoma | 1,000 sq ft | None required | 24 ft | TMC 13.06.150. Pre-approved DADU plans available. |
| Kirkland | 1,200 sq ft | 1 stall | 25 ft | KZC 115 — allows ADUs in all residential zones. |
| Redmond | 1,000 sq ft | 1 stall | 24 ft | RZC 21.08.140. Streamlined DADU permit. |
| Renton | 1,000 sq ft | 1 stall | 24 ft | RMC 4-2-110. Updated 2024 to match HB 1337. |
| Everett | 1,000 sq ft | 1 stall, waived near transit | 24 ft | EMC 19.06. Two ADUs allowed per HB 1337. |
| Auburn | 1,000 sq ft | 1 stall | 24 ft | ACC 18.31.140 — updated 2024. |
| Federal Way | 1,000 sq ft | 1 stall | 24 ft | FWRC 19.195. HB 1337 implementation pending. |
| Kent | 1,000 sq ft | 1 stall | 23 ft | KCC 15.08.350. Updated 2024. |
Source: City municipal codes + WA Dept of Commerce HB 1337 tracker (2025). Verify with the city permit center before designing.
Frequently asked
Does HB 1337 apply to my city?+
HB 1337 applies to all Washington cities and counties planning under the Growth Management Act — which is every Puget Sound jurisdiction. Smaller, non-GMA cities are encouraged but not required to adopt.
When did the law take effect?+
HB 1337 was signed in May 2023 with a compliance deadline of six months after the city's next periodic comprehensive plan update (most King/Pierce/Snohomish cities by mid-2024).
Can I rent my ADU short-term (Airbnb)?+
State law does not prohibit short-term rentals in ADUs, but individual cities may. Seattle limits short-term rentals to a primary residence; Tacoma allows them with a license. Always check the local code before listing.
Do I need a separate utility connection?+
State law does not require separate water/sewer/electric meters for ADUs. Some cities still require separate electric service for DADUs over 800 sq ft — check local code.
Can the ADU be sold separately from the main house?+
Yes. RCW 36.70A.681(1)(h) requires cities to allow ADUs to be condominiumized and sold separately. Implementation is rolling out city by city — Seattle, Tacoma, and Bellevue allow it as of 2025.
Are there design review requirements?+
Most cities exempt ADUs from full design review but require basic façade compatibility (siding, roof pitch, window placement). Seattle, Bellevue, and Kirkland have published ADU design guidelines.
Statute & official sources
- Source ↗RCW 36.70A.681 — Accessory Dwelling UnitsFull statute text
- Source ↗HB 1337 (2023) Bill TextEngrossed substitute
- Source ↗WA Dept of Commerce — ADU GuidanceModel code, FAQ
- Source ↗Seattle Municipal Code 23.44.041City ADU standards
- Source ↗Bellevue LUC 20.20.120City ADU standards
- Source ↗Tacoma Municipal Code 13.06.150Pre-approved DADU plans
Continue researching
Need help applying the law to your lot?
We're a WA-licensed general contractor (GOLDNAB882L2) who has built ADUs under HB 1337 in every major Puget Sound jurisdiction. Free feasibility review for any property in our service area.
Request a feasibility review →