Multnomah County, OR Accessory Structures: Tiny Homes (2026)
Tiny home rules in Multnomah County, OR, covering tiny houses on wheels (THOWs), park model RVs, and tiny home on foundation builds, determine where they are legal and how they get permitted.
Key Facts
- ADU location
- Must sit inside urban growth boundary
- Barred designs
- RVs, park models, yurts excluded
- Size cap
- 800 sq ft or 75% of house
- Rental limit
- Short-term rental of ADU prohibited
- Coverage
- Unincorporated MUA-20 land only
Summary
In Multnomah County's Multiple Use Agriculture (MUA-20) zone, an accessory dwelling unit must be a permanent structure: recreational vehicles, park model RVs, yurts, and similar non-permanent designs are barred from qualifying as an ADU on unincorporated rural land.
(7) The following designs are not permitted for use as an ADU: Recreational vehicle, park model recreational vehicle, yurt or any other similar design not intended for permanent human occupancy or any structure unable to meet all applicable construction or installation standards.
Full Breakdown
Multnomah County Code § 39.4310(L) allows one accessory dwelling unit on a Multiple Use Agriculture (MUA-20) lot, but only if it sits entirely inside the urban growth boundary and meets construction standards. Subsection (L)(7) is explicit that a tiny home built as an RV, park-model RV, or yurt cannot count as the ADU: only a permanently built structure will qualify. The ADU is also capped at 800 square feet or 75% of the main house's floor area, whichever is smaller, and short-term rental of it is barred by recorded covenant. This governs unincorporated county land only, not Portland, Gresham, Troutdale, Fairview, or Wood Village.
Violations & Fines
A wheeled tiny home, RV, or yurt sited as an ADU does not meet the allowed-use standard and is subject to county zoning code enforcement as an unpermitted use, up to and including a removal order.
Frequently Asked Questions
Can I put a tiny house on wheels in as an ADU in Multnomah County?
Does this rule cover Portland?
How big can a legal ADU be instead?
Sources & Official References
Other rules in Multnomah County
Compare Multnomah County to another location·View the Oregon accessory structures overview
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