ADU (accessory dwelling unit) Rules and Regulations in Marion County, OR (2026)

In Marion County, the ADU rules depend on where your parcel sits. The county covers urban-area properties (outside city limits) and rural-area properties under two different ordinances, with different size, setback, height, and rental standards. Cities in the county apply their own requirements. Before you pick a model, confirm which set of rules, fees, and application steps applies to your address.

Where ADUs are allowed

Marion County allows ADUs differently depending on whether your property is in an urban or rural area.

Urban areas (outside city limits), adopted via Ordinance #1382 (2017):

• Urban Transition Zone: interior or attached ADUs only.
• Single Family Residential and Urban Development zones: interior, attached, or detached ADUs.

Rural areas, adopted via Ordinance #1458 (January 2024):

• Allowed in the Acreage Residential (AR) zone on parcels at least 2 acres in size under MCC 17.128.020(K). The handout says “greater than two acres,” but the code threshold is at least 2 acres.
• Not permitted in other rural zones.

The ordinary urban and rural ADU paths described here allow one ADU. A separate historic-dwelling conversion provision has different conditions; do not assume it applies to a new modular ADU.

Size limits

• Urban ADUs: 900 square feet in floor area, or 75% of the footprint of the main dwelling, whichever is less.
• Rural ADUs: 900 square feet of living space.

Setbacks

Setback standards depend on the area and whether the ADU is attached, interior, or detached.

Urban (non-Salem areas):

• Attached or interior ADUs follow the same setbacks as the primary dwelling.
• Detached ADUs follow accessory structure setback standards.

Urban (Salem area):

• Detached: 5 feet from rear property lines, 3 feet from side property lines.
• Attached or interior: follow the primary dwelling setbacks under MCC 16.26.100(B); confirm the underlying zone rather than applying a blanket attached-unit setback.

Rural:

• Attached or interior ADUs follow the same setbacks as the primary dwelling.
• Detached ADUs follow the residential structure setbacks in MCC 17.117.
• A rural ADU must be within 100 feet of the primary dwelling.
• Special resource-zone buffers under MCC 17.128.050 can further restrict placement.

Height limits

• Urban ADUs: Detached ADUs are limited to 25 feet; attached and interior ADUs follow the primary dwelling’s standards.
• Rural ADUs: Up to 35 feet, the same as primary dwellings.

Water, septic, and sewer

The published rules call out one specific water requirement, which applies to rural properties in the Sensitive Groundwater Overlay (SGO) zone:

• The ADU must be connected to a 1,000-gallon water storage tank for use with the primary well.
• An SGO declaratory agreement must be recorded into the deed.

MCC 17.128.020(K) also requires necessary septic disposal permits and excludes urban reserves and specified water-restricted areas from the ordinary rural ADU path. Confirm approved water and wastewater capacity before locating the home, driveway, or deck. An existing drainfield does not establish permission to connect another dwelling.

Rental rules

Marion County’s rules are written to prevent ADUs from being used as short-term rentals:

• Urban ADUs: Rentals must have a minimum duration of 30 days.
• Rural ADUs: Rentals must have a minimum duration of 45 days.

For qualifying urban ADUs, ORS 197A.425 bars a requirement that the owner occupy either dwelling. Do not transfer older urban handout provisions or rules for a different housing type into an ADU application.

Parking

• Urban ADUs: The older county handout still mentions an extra parking space, but ORS 197A.425 prohibits requiring construction of additional off-street parking for qualifying urban ADUs. Use current code and state law for the application.
• Rural ADUs: The published rules summarized here do not state a specific rural parking requirement.

For urban properties, note that no new curb cuts are permitted, though existing curb cuts may be expanded with an approved access permit.

Permit and application process

Urban ADUs:

• A building permit from the Marion County Building Inspection Division is required.
• The county handout says a qualifying ADU does not require a separate land-use application. Zoning compliance and applicable building, utility, and access approvals still need review.
• A deed restriction must be recorded.

Rural ADUs:

• Building permits from the Marion County Building Inspection Division must be obtained.
• The rural handout describes a path without a separate land-use application for qualifying proposals; confirm that your proposal meets its conditions.
• State statutory thresholds cannot be varied by Planning.
• Local fire access, evacuation, and applicable defensible-space requirements need review; show evacuation and staging areas on the site plan.
• Record the required compliance agreement.
• A rural ADU may have a separate driveway if an access permit is issued by Marion County Public Works.

County-specific notes

• Structures on wheels are not allowed as ADUs. This includes recreational vehicles, park models, and tiny homes on wheels (which are built to RV standards).
• Modular homes are allowed as ADUs because they are built to IRC (International Residential Code) standards and placed on foundations. A manufactured home may also be allowed as an ADU if it meets ADU standards and is Energy Star certified with the proper HUD (the federal standard for manufactured homes) certification label.
• A rural ADU cannot be divided off from the parcel containing the main dwelling. Confirm any different ownership proposal through a separate jurisdiction review.

Wolf homes are built in our Battle Ground factory and delivered into Oregon as modular structures, which Marion County’s rules allow as ADUs. The structure is reviewed through the state program, while the property still needs local placement, foundation, utility, and inspection approvals.

Start with your parcel

Send us the address and intended use, and we will start with jurisdiction, zoning, setbacks, utilities, and model fit.

For statewide background, read our Oregon ADU rules guide. To compare units, see the Wolf model lineup.

Ready to find out what your parcel can support? Get a free Wolf property evaluation.

This is general information, not legal advice. Confirm current rules, fees, and application requirements with Marion County or the city that has jurisdiction over your property.