Accessory Structures in Multnomah County, OR (2026)
4 county-level rules, plus city-specific rules for 2 cities in Multnomah County, Oregon.
Verified from official government sources
ADU Rules
In the Rural Residential zone, unincorporated Multnomah County allows one accessory dwelling unit per single-family lot, capped at 800 square feet or 75% of the main house's size, but only on land sitting entirely inside the urban growth boundary.
Multnomah County ADU Permit Rules
Some RestrictionsMultnomah County Code § 39.4360(L)(1), (4)
(L) Accessory Dwelling Unit (ADU), subject to the following standards: (1) The ADU is sited entirely inside the urban growth boundary. ... (4) The floor area of the ADU shall not exceed either 800 square feet, or 75% of the floor area of the single-family dwelling to which the ADU is accessory, whichever is less.
ADU Rental Restrictions
Multnomah County bars short-term rental of accessory dwelling units in rural residential zones like MUA-20 outside Portland; owners must record a covenant limiting the ADU to long-term occupancy.
ADU Short-Term Rental Ban, Multnomah County
Significant RestrictionsMultnomah County Code § 39.4310(L)(8)-(9)
(8) Short-term rental of the ADU is prohibited. For purposes of this subsection, short-term rental is defined as fee-based occupancy for a period less than 30 consecutive calendar days. ... (9) The land owner shall sign and record with the county a covenant stating that the ADU cannot be used for short-term rental, as defined in this section.
Shed & Carport Rules
In unincorporated Multnomah County's LR-5 residential zone, a detached carport must sit behind the house's rear line or at least 50 feet from the front lot line, and can't exceed the main house's height or footprint.
Carport Setbacks in Multnomah County
Some RestrictionsMultnomah County Code § 39.4824(A)
(A) Accessory buildings such as garages, carports, studios, pergolas, private workshops, playhouses, private greenhouses or other similar structures related to the dwelling in design, whether attached or detached, provided: ... (3) If detached and located behind the rear-most line of the main building, or a minimum of 50 feet from the front lot line, whichever is greater, a one-story accessory ...
Tiny Homes
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.
Multnomah County Bars Tiny Homes as ADUs
Significant RestrictionsMultnomah County Code § 39.4310(L)(7)
(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.
Accessory Structures by City in Multnomah County
2 cities in Multnomah County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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