Accessory dwelling units
ADUs & DADUs.
Detached and attached accessory dwelling units add significant value to Seattle properties — whether you're building for rental income, family housing, or a dedicated workspace. We've built dozens across Seattle and the PNW.
Seattle rental demand is strong. A quality DADU can generate meaningful income while appreciating your property value.
Keep aging parents or returning kids close without giving up your privacy. A complete home steps from your door.
A dedicated space for art, music, writing, or remote work. The commute is a 30-second walk.
Detached — a fully separate structure in your backyard.
Attached — above a garage, in a basement, or as an addition.
An ADU (accessory dwelling unit) is attached to or within the primary home — a basement conversion, for example. A DADU (detached accessory dwelling unit) is a separate structure, like a backyard cottage. Seattle's zoning treats them somewhat differently, and lot size, coverage limits, and parking requirements determine which is feasible on a given property.
Most DADUs run $180,000–$350,000 depending on size, finish level, and site access — a DADU on a lot with difficult alley access or utility connections costs meaningfully more than one on a straightforward flat lot. We give a real number after a site visit, not a generic range.
Realistically 4–8 months for permit approval, depending on the current backlog at Seattle DCI and whether your lot has any critical areas or tree protection complications. We tell clients this upfront rather than promising an optimistic timeline that falls apart.
Seattle's current regulations allow ADU and DADU rentals, though owner-occupancy requirements have changed over the years — we recommend confirming current rules with the city directly since regulations are revised periodically.