ADUs are allowed in RainierTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Rainier, OR
Is your property eligible for an ADU?
# of Properties
1,063
Owner-occupied
59%
Zoning districts
13
Median Lot Size
0.22 acres
Avg Income
$83,085
Residential Types:
1,063 housing units
Single Family
12%
2-3 Family
5%
Other
84%
Zoning Districts:
1,213 parcels · 13 districts
R-2
49%(593)
R-3
15%(186)
R-1
12%(144)
C-2
9%(109)
Other
15%(181)
ADU Rules
What can you build in Rainier, OR?
Rainier, OR follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: Conditional Use Permit
- –Detached ADU: Conditional Use Permit
Interior / Attached ADU Size Limits
- –Maximum gross habitable floor area for an internal ADU (in-home apartment) is 800 sq ft.
Detached ADU Size Limits
- –Maximum GHFA for a detached ADU: 800 sq ft (single-family parcels in R-2; conditional use).
Max Units
- –R-2 single-family: 1 ADU per lot (conversion/addition/detached).
- –Duplex, multifamily, or outside R-2: 0 ADUs.
Owner Occupancy
- –Owner must occupy principal unit or ADU at least six months.
Parking
- –1 additional space/ADU (in addition to SFD); no waivers stated
Rental Restrictions
- –Owner-occupied unit may not be rented; no stated minimum lease term or short-term rental limits.
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.
Columbia County