Multnomah County, OR Accessory Structures: Tiny Homes (2026)

Oregon is a national leader on small-home regulation. Foundation-built tiny houses qualify as Accessory Dwelling Units (ADUs) under ORS 197.312(5), which requires every Oregon city with 2,500+ population to allow at least one ADU per single-family lot. Portland City Code 33.205 allows up to TWO ADUs per lot (one attached, one detached) up to 800 sq ft or 60% of primary dwelling floor area (whichever smaller), with no off-street parking required and NO owner-occupancy requirement (HB 2001, 2019). Multnomah County allows ADUs in unincorporated areas under MCC 39.3030 subject to zoning. Oregon adopted IRC Appendix Q for tiny houses under 400 sq ft, allowing reduced ceiling heights (6'8") and loft ladders as legal stairs. Tiny Houses on Wheels (THOWs) fall under ORS 446 as park-model recreational vehicles — they can be placed in licensed RV parks and, under Portland PCC 33.296.070, used as temporary dwellings during construction of a primary structure for up to 2 years. Portland also pilots RV/tiny-home villages (Safe Rest Villages) under city housing emergency authority. SB 391 (2021) allowed counties to permit one rural residential RV dwelling on an existing farm-use parcel. Sewer/septic connection per DEQ OAR 340-071 is required for any permanent dwelling. Tiny homes cannot be used as STRs under PCC 33.207 if they are ADUs located on a lot where the owner does not occupy the primary dwelling.