ADU Permits: Kent vs Seattle
How do adu permits rules compare between Kent, WA and Seattle, WA?
Seattle has fewer restrictions than Kent.
Kent, WA
King County
Kent permits accessory dwelling units under KCC 15.08.250, updated June 2023 to implement Washington HB 1337 (RCW 36.70A.681). Up to two ADUs are allowed per single-family lot, each up to 1,000 square feet and 24 feet tall. Building permits are filed through the Kent Permit Center using the regional MyBuildingPermit.com portal.
View full Kent 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 | Kent | Seattle |
|---|---|---|
| Code Section | KCC 15.08.250 | SMC 23.42.054, 23.44.041 |
| ADUs Per Lot | Up to 2 (per HB 1337) | Up to 2 (HB 1337) |
| Max Size Each | 1,000 sq ft | - |
| Max Height | 24 feet | - |
| State Law | RCW 36.70A.681 | - |
| 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.
Kent FAQ
Do I need a permit to build an ADU in Kent?
Yes. A building permit is required through the Kent Permit Center, filed via MyBuildingPermit.com. The ADU must meet KCC 15.08.250 standards and the 2021 I-Codes as adopted by Washington. Electrical work requires a separate Washington L&I permit, and final inspection sign-off is required before occupancy.
How many ADUs can I build on my Kent lot?
Up to two ADUs per single-family lot under KCC 15.08.250, consistent with Washington HB 1337 (RCW 36.70A.681). They may be two attached units, two detached units, or one of each, and each is capped at 1,000 square feet and 24 feet in height.
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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