ADU Permits: Bellevue vs Seattle
How do adu permits rules compare between Bellevue, WA and Seattle, WA?
Seattle has fewer restrictions than Bellevue.
Bellevue, WA
King County
Bellevue permits accessory dwelling units under Land Use Code (LUC) 20.20.120, substantially amended by Ordinance 6746 (2023 ADU Reform LUCA). Washington HB 1337 (RCW 36.70A.681) requires Bellevue to allow up to two ADUs per lot in urban growth areas, and the city's middle-housing LUCA is being adopted to comply by the June 30, 2025 statewide deadline.
View full Bellevue rules →Seattle, WA
King County
Seattle permits attached (AADU) and detached (DADU) accessory dwelling units ministerially under SMC 23.42.054 and 23.44.041, with HB 1337 (2023) requiring up to two ADUs per residential lot statewide. Applications are filed with Seattle Department of Construction & Inspections (SDCI) and SDCI must act within 120 days (Type I land-use review).
View full Seattle rules →Key Facts Comparison
| Fact | Bellevue | Seattle |
|---|---|---|
| Code Section | LUC 20.20.120 | SMC 23.42.054, 23.44.041 |
| Reform Ordinance | No. 6746 (2023) | - |
| Max Size | 1,200 sq ft or 40% of structure | - |
| State Law | HB 1337 / RCW 36.70A.681 | - |
| ADUs Per Lot | Up to 2 (state-mandated) | Up to 2 (HB 1337) |
| Permit Portal | MyBuildingPermit.com | - |
| Review Type | - | Type I ministerial |
| SDCI Review Clock | - | 120 days max |
| Pre-Approved Plans | - | ~30-day review |
Highlighted rows indicate differences between cities.
Bellevue FAQ
Do I need a permit to build an ADU in Bellevue?
Yes. A building permit is required, filed through MyBuildingPermit.com, and a final land-use planner inspection is required before occupancy. Registration and public noticing were removed by Ordinance 6746 (2023), but the construction permit itself remains mandatory.
How big can my ADU be in Bellevue?
LUC 20.20.120 allows an ADU up to 1,200 square feet or 40 percent of the primary structure, whichever is larger. Attached ADUs must comply with the same height and setback rules as the primary residence.
Seattle FAQ
How many ADUs can I have on a Seattle lot?
Up to two, per SMC 23.42.054 and Washington HB 1337. Options include one AADU and one DADU, or two DADUs on lots that meet the size and access requirements.
How long does an ADU permit take in Seattle?
SDCI must complete Type I review within 120 days. Pre-approved DADU plans typically clear review in 30-45 days. Custom designs commonly take 90-120 days plus revisions.
Does Seattle require design review for ADUs?
No. SMC 23.42.054 establishes ADUs as Type I ministerial — no design review, no public notice, and no neighborhood meetings are required.
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