Garage conversion rules in Seattle, WA — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
Garage conversions to ADUs are allowed in Seattle under SMC 23.42.022 as part of HB 1337 compliance. Conversion provisions apply in all residential zones. Building permits required from SDCI. Must meet Seattle Building Code and accessibility standards.
Seattle explicitly permits garage conversions to ADUs under Washington State HB 1337, which allows conversions even when the existing garage does not meet current setback or lot coverage requirements. A Construction Addition/Alteration Permit from SDCI is required. The converted space must meet all Seattle residential building, mechanical, electrical, and energy code requirements for habitable space. Electrical, plumbing, and mechanical permits are also needed. DADU size limit is 1,000 square feet (not including garage or bike storage). Historically, the land use code required proof of alternative on-site parking, but the 2025 zoning changes have relaxed parking requirements, especially within half a mile of major transit stops. If the garage was built before 1957 or has an existing building permit on file, the conversion process is more straightforward. Garage conversions have become increasingly popular as Seattle housing costs continue to rise.
Unpermitted conversion: SDCI stop-work order. Non-code-compliant habitation: notice of violation and potential fines.
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Side-by-side rule comparisons with other cities in King County.
See how other cities in King County handle garage conversions.
See how Seattle's garage conversions rules stack up against other locations.
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