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Seattle ADU guides
Answers for Seattle homeowners, checked against city and Washington sources as of November 2026.
Guides
What are the ADU rules in Seattle?
Counts, size, height, parking and owner rules.
Read the guideCan I build two ADUs in Seattle?
Combinations and how the unit count works.
Read the guideDo ADUs need parking in Seattle?
No off-street parking for ADUs.
Read the guideHow much does an ADU cost in Seattle?
Published Seattle ranges by type and per square foot.
Read the guideHow long does it take to build an ADU in Seattle?
SDCI review, corrections and construction.
Read the guideIs your lot ready for an ADU?
Send your address and a sentence about what you want. We look up the zoning, setbacks and utility routes and reply with the ADU types that fit.
We build in Seattle, WA.