Seattle Accessory Dwelling Unit Guide
Data version: Q2 2026 · Last updated 2026-05-13
Buildability City Score™: B+ (Top 32%) · Median permit time: 72 days
TL;DR. Find out if your Seattle property qualifies for an accessory dwelling unit. Buildability™ checks the local ADU ordinance, Washington state law, your zoning district, lot size, setbacks, parking requirements, and owner-occupancy rules in about 20 seconds. Free for your first check.
Seattle ADU rules at a glance
Seattle follows local ordinances layered on top of Washington state ADU law. Typical restrictions cover maximum size (often 800–1,200 sqft), height (16–25 feet), side setbacks (4 feet minimum in most jurisdictions), parking (often waived near transit), and owner-occupancy. Buildability™ reads Seattle's specific code against your exact lot.
Why this matters
Most Seattle homeowners don't discover their ADU is infeasible until they've spent $3,000+ on preliminary design. Buildability™ catches the blockers first — easements, overlays, wetland proximity, utility extension costs — so you don't waste soft costs on a dead-end project.
How Buildability™ checks your Seattle property
Enter any Seattle address. Buildability™ pulls zoning, lot dimensions, easements, environmental overlays, utility access, and current Washington state ADU law. Results include your Buildability Score™, setback envelope, maximum ADU size, parking waiver eligibility, and an estimated permit timeline — in about 20 seconds. Free for your first check.
Help us keep this accurate
Buildability™ translates Seattle's ADU rules in plain language. Rules change and overlays are sometimes missed — if you spot an error on this page, email team@buildability.us with the URL and what's off. We verify with the Seattle planning department and update within 48 hours of a confirmed correction. Seattle planning staff: the same email works if you'd like to flag corrections or set up a direct verification channel.
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