What can you build on your lot?

Type a King County address. We look up the parcel in the county’s own records, work out which city it sits in, pull that city’s zoning for the exact point, and apply the ADU rules we have verified against municipal code — with every answer citing the section it came from.

Beta Three cities wired in so far. It tells you when it doesn’t know something rather than guessing — see methodology.

How it can be wrong

• It does not see your lot. Easements, critical areas and their buffers, covenants, overlays, historic designations, and shoreline jurisdiction can all restrict a parcel further than its zoning does. None of those are in the data this tool reads.
• Some facts simply are not published. King County exposes no building-square-footage field, so rules that depend on your existing house’s floor area cannot be resolved. Nor does anything published tell us whether your lot backs onto an alley — which, in Seattle, is the difference between a five-foot rear setback and none at all.
• Kirkland does not publish a zoning map we can query. It publishes comprehensive-plan designations, which are a different thing, so we leave Kirkland’s zone-dependent rules unresolved rather than substituting the wrong layer.
• Address matching is imperfect. The county geocoder will confidently match a street in the wrong city, so we cross-check every match against the jurisdiction boundary and refuse the lookup when the two disagree. You will occasionally get a refusal on a real address.

The rules themselves come from the same verified corpus as the rest of this site, and corrections are logged in the changelog. If this tool tells you something your city contradicts, the city is right and we want to hear about it — see about.