Pierce County ADU rules: Washington's ADU law (HB 1337)
Washington's HB 1337 (2023) requires cities and counties to allow at least two accessory dwelling units (ADUs) on lots zoned for houses inside an urban growth area. In Pierce County, that is 223,650 of 329,418 lots. Another 80,525 lots are outside the urban growth area, where the county's own ADU rules decide.
Check the zoning: the law applies where the zone allows a house.
Check the urban growth area: every city is inside one; outside cities, the county's map decides.
Check for septic: an ADU on a septic system needs the health department to approve the system's capacity (20,349 of the qualifying lots look to be on septic).
Check for mapped critical areas (wetland, landslide, erosion, flood, a stream buffer): the state rule does not apply to those lots (34,416 lots here), and local rules decide.
It requires cities and counties to allow at least two ADUs on lots zoned for houses inside an urban growth area. Local rules on size, height, parking and utilities still apply.
How many lots in Pierce County does it cover?
223,650 of the county's 329,418 lots are zoned for houses inside an urban growth area.