ADUs are allowed in Unincorporated MultnomahTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Unincorporated Multnomah, OR
Is your property eligible for an ADU?
# of Properties
9,439
Owner-occupied
62%
Zoning districts
66
Avg Home Value
$348,385
Median Lot Size
2.07 acres
Avg Income
$142,622
Residential Types:
9,439 housing units
Single Family
32%
Other
68%
Zoning Districts:
9,797 parcels · 66 districts
MUA20
13%(1,300)
R20
13%(1,259)
RR
10%(1,019)
CFU2
10%(948)
Other
54%(5,271)
ADU Rules
What can you build in Unincorporated Multnomah, OR?
Unincorporated Multnomah, OR follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum size of 800 sq ft
- –Maximum size of 75% of the floor area of the primary single-family dwelling
Detached ADU Size Limits
- –Maximum size of 800 sq ft
- –Maximum size of 75% of the floor area of the single-family dwelling
Parking
- –No explicit ADU parking min or max; parking for unspecified uses may be assigned by the Planning Director to the nearest listed use; ADUs must share the primary dwelling's driveway entrance with the SFD; no variance to the shared-driveway requirement.
Rental Restrictions
- –Short-term rentals (<30 days) prohibited; long-term month-to-month rentals permitted; owner must record a covenant with the county prohibiting short-term use
ADU State Law
What can you build in Oregon?
- –In urban growth areas, Oregon law requires cities and counties to allow at least one ADU on lots zoned for detached single-family homes.
- –Local jurisdictions cannot require owner occupancy for ADUs, but may regulate short-term or vacation rentals.
- –There are no statewide limits on ADU size, height, setbacks, lot size, or floor area ratio. Local zoning rules apply.
- –Parking requirements, if any, are set by the local jurisdiction, subject to state limitations.
- –Some cities may allow more than one ADU per lot, depending on local code.
- –Oregon law does not require counties to allow ADUs in rural residential zones. Whether an ADU is allowed depends on county zoning.
- –ADUs in rural residential areas cannot be used for short-term or vacation rentals.
- –Additional requirements may apply related to wildfire risk, water supply, septic capacity, and fire access.
- –Counties may impose additional restrictions beyond state law or choose not to allow ADUs at all.
- –If a county allows ADUs, state law imposes strict limits, including a minimum 2-acre lot size, a maximum ADU size of 900 sq ft, a location within 100 ft of the primary dwelling, and a limit of one ADU per parcel.
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other Oregon municipalities
Rules change at the town line. Check the municipality your property is actually in.
Multnomah County