Seattle’s ADU guidance describes a separate living space within a house or elsewhere on the same property and directs owners to current City code. The City says a property may have four or more total units while only two may be ADUs. Start with Seattle’s current ADU guidance and Seattle Municipal Code §23.42.022, not an older tip sheet that the City warns may be out of date.
Compare the local screen with Washington’s rule
Washington law requires covered cities and counties to allow at least two ADUs on lots within an urban growth area in zoning districts that allow single-family homes, in specified attached and detached combinations. It also says qualifying cities and counties may not require owner occupancy of the lot. The statute preserves exceptions for designated critical areas and buffers, and for a specified impaired or threatened reservoir watershed.
The state minimum does not establish that a particular Seattle parcel qualifies. Verify the current Seattle zone, the City’s implementation, the urban-growth-area and statutory conditions, and any mapped exception. Older Seattle tip sheets may not reflect interim rules effective in 2025.
Use the current City code and confirm the property’s map and site conditions before relying on an ADU count. Building permits, critical-area review, and other site-specific approvals remain separate.