Auburn, WA Accessory Structures: Tiny Homes (2026)

Auburn treats tiny homes in two distinct categories. Tiny homes on permanent foundations, if they meet the 2021 Washington State Residential Code (IRC Appendix Q for dwellings under 400 sq ft), are permitted as either primary single-family dwellings or as ADUs under ACC 18.31.120. These require a building permit, conventional utility connections, and must meet all zoning setbacks, height limits, and design standards. IRC Appendix Q allows reduced stair, ceiling height, and loft standards for homes up to 400 sq ft. Tiny homes on wheels (THOWs) are classified as either recreational vehicles (RVs, under ANSI A119.5) or park-model RVs (under ANSI A119.5) and may only be occupied as permanent dwellings in approved RV parks or manufactured home communities, not on private residential lots. Washington HB 1110 (2023) authorizes middle housing but not THOWs as stand-alone dwellings on single-family lots. Short-term camping in an RV or THOW on private property is limited under ACC 10.36 (typically no more than 14 consecutive days). Foundation-ready tiny homes built to IRC and factory-built per RCW 43.22 can be placed as legal ADUs. Pallet shelters and sanctioned encampments fall under separate homeless services framework.