Tacoma, WA Accessory Structures: Tiny Homes (2026)

Washington adopted the 2018 IRC including Appendix Q (Tiny Houses) effective July 1, 2021, and Tacoma applies it through Building Code TMC Title 2.02. Appendix Q sets life-safety standards specifically for site-built tiny houses on a permanent foundation of 400 square feet or less, including stair, ladder, loft, and emergency-escape requirements that differ from standard IRC dwelling-unit rules. In Tacoma the most common path for placing a tiny home in a backyard is to permit it as a Detached Accessory Dwelling Unit (DADU) under TMC 13.06.150. Per the Tacoma Permits ADU tip sheet, a DADU must observe a minimum 5-foot setback from side property lines (8 feet if a main entrance faces a side property line) and a minimum 15-foot rear setback, except no setback is required from an alley. ADUs are capped at 1,000 square feet or 85 percent of the primary residence's size, whichever is less. Existing buildings being converted to a DADU are not required to meet the setbacks above but must meet adopted Building Codes at the time of permit application. The Home In Tacoma Zoning and Standards package, approved by City Council in November 2024 and effective February 1, 2025, broadens the residential zones where ADUs, rowhouses, and a wider range of housing types are permitted and updates parking and tree-code provisions. Tiny houses on wheels (THOWs) are regulated as recreational vehicles by Washington L&I and are not allowed as permanent dwellings on residential lots without a separate authorization. Confirm current setbacks and review timelines with Planning and Development Services at 253-591-5030.