King County, WA Accessory Structures: ADU Permits (2026)
How to apply for an ADU building permit: application steps, plan-check requirements, review timelines, ministerial vs discretionary review, and which department to file with.
Research in progress
We are currently verifying King County's specific local ordinance for adu permits. In the meantime,Washington state law generally applies, and below you'll find guidance for finding the official rules and links to related King County ordinances we've already verified.
Washington State Law Context
Washington state law provides the baseline framework for adu permits across all municipalities in the state. Individual cities like King County may adopt additional local rules on top of state requirements, which is what makes checking your specific city ordinance important. For King County residents, the safest approach is to follow state law as a baseline and contact City Hall for any additional local requirements.
You can browse all Washington accessory structures to see how cities across the state regulate this topic.
How to find official King County ADU Permits rules
- Search for "King County WA municipal code" to find your city's online code portal (Municode, eCode360, or American Legal Publishing are the most common).
- Look for chapters covering accessory structures, zoning, nuisance, or property maintenance — that's where most adu permits rules live.
- Contact King County City Hall's code enforcement, planning, or community development department for clarification.
- Check with your HOA if applicable — many HOAs have stricter rules than the city itself.
Other accessory structures verified for King County
We've verified the following accessory structures for King County: