Seattle ADU Guides

Plain-language guides to building an accessory dwelling unit in Seattle.

Seattle ADU Cost Guide: Permits, Fees, and What to Expect (2026)

A practical guide to Seattle ADU costs — verified 2026 permit fees, the King County sewer capacity charge, and what drives total project cost. Not a quote — get itemized bids from verified builders.

Last reviewed July 2026

Seattle ADU Rules: A Guide to Current Regulations

A plain-language guide to Seattle's accessory dwelling unit rules — what's allowed, where, at what size, and how permitting works. Not a substitute for professional advice.

Last reviewed July 2026