ADU rules in Pierce County, WA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Unincorporated Pierce County allows accessory dwelling units under PCC 18A.37.120. Two ADUs are permitted per lot inside an Urban Growth Area and one outside, attached or detached, with size caps and a building permit.
Pierce County Code 18A.37.120 governs ADUs in unincorporated areas, updated to comply with Washington's HB 1337. Two ADUs are allowed per lot of record inside the Urban Growth Area (UGA) and one ADU outside the UGA, in any attached/detached combination on single-family lots. An ADU may not exceed 1,000 square feet inside the UGA, rising to 1,250 square feet outside the UGA, measured as interior habitable area excluding garages. Owner-occupancy is no longer required, so an ADU may be rented as an investment unit. A building permit is required, and conversion of an existing detached structure to an ADU is allowed within side or rear setbacks inside the UGA.
Building an ADU without a permit, exceeding the 1,000/1,250 square-foot cap, or ignoring setback and design standards can trigger stop-work orders, code enforcement, and required corrections or removal.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
pierce-county-wa
Backyard residential composting is allowed and encouraged in Pierce County with no permit, but a compost pile that creates odor, attracts vermin, or otherwis...
pierce-county-wa
Pierce County has no ordinance specifically prohibiting or permitting synthetic/artificial turf on residential lots. Installation must still meet general zon...
pierce-county-wa
Pierce County encourages native and drought-tolerant plantings and requires native-vegetation retention on many development sites, but homeowners are free to...
pierce-county-wa
Rooftop rainwater collection is broadly allowed in Washington, and Pierce County has no ordinance prohibiting residential rain barrels or cisterns; larger sy...
pierce-county-wa
Pierce County government sets no county-wide residential watering schedule; outdoor watering rules are set by your water provider — mainly Tacoma Water and l...
pierce-county-wa
Every Pierce County landowner has an enforceable duty under RCW 17.10.140 to eradicate class A noxious weeds and control listed class B and C weeds. The Pier...
See how Pierce County's adu rules rules stack up against other locations.
Help us keep this page accurate. If you notice an error or outdated information, let us know.