Free tool · Snohomish County
What can you build on your lot?
Type an address. See the lot to scale, what’s on it now, and what Washington law now lets you add: backyard cottages, garage conversions, and in some cities, more homes on the same lot.
What changed in Washington
Inside urban growth areas, cities and the county must allow two accessory dwelling units on lots that allow a house: attached, detached, or one of each.
An ADU that size must be allowed. You can’t be required to live on site, and ADU impact fees are capped at half of what a new house pays.
Cities of 25,000 or more must allow at least two homes on residential lots, and cities of 75,000 or more at least four, with more near major transit.
Sources: Washington State Department of Commerce, ADU guidance (RCW 36.70A.680 and .681) and its middle housing fact sheet for E2SHB 1110; Snohomish County GIS parcels, roof outlines, zoning, urban growth areas and city limits; city populations from the Office of Financial Management’s April 1, 2025 estimates. A quick screen, not a legal or zoning opinion.