King County, WA Accessory Structures: ADU Impact Fees (2026)
Impact fees, school fees, utility hookup charges, and waivers for ADUs. Many jurisdictions exempt ADUs under 750 sq ft from impact fees per state law.
Research in progress
We are currently verifying King County's specific local ordinance for adu impact fees. 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 impact fees 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 Impact Fees 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 impact fees 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: