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Marion County, OR Accessory Structures: ADU Rules (2026)

Few Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Marion County, OR, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

State ADU mandate: ORS 197.312(5) (HB 2001)
Applies to: Detached SFR in UGB
Owner-occupancy required?: No, prohibited by statute
Extra parking required?: No, prohibited by statute
Local codes: Salem, Keizer, Woodburn, county

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Oregon under recent ADU streamlining laws. The Marion County, OR rules below cover local size, height, and setback requirements.

Summary

Oregon law requires Marion County and its cities to allow at least one accessory dwelling unit (ADU) for each detached single-family home in urban-growth-boundary residential zones, subject only to reasonable siting and design rules. Owner-occupancy and extra off-street parking cannot be required.

City-specific rules exist: Salem has its own adu rules rules that differ from Marion County's county-level regulations. If you live in Salem, check the city-specific page instead.

A city with a population greater than 2,500 or a county with a population greater than 15,000 shall allow in areas within the urban growth boundary that are zoned for detached single-family dwellings the development of at least one accessory dwelling unit for each detached single-family dwelling, subject to reasonable local regulations relating to siting and design.

View official code

Official source re-checked September 8, 2026: the cited page had not changed since it was quoted.

Full Breakdown

Under House Bill 2001 (2019), codified at ORS 197.312(5), a county with a population greater than 15,000, like Marion County (about 347,000), must allow one ADU per detached single-family dwelling on land zoned for such dwellings within an urban growth boundary. An ADU can be an interior, attached, or detached unit. Salem, Keizer, and Woodburn implement this in their development codes. Critically, local regulations relating to siting and design cannot include owner-occupancy requirements or a demand for additional off-street parking. In the unincorporated rural county, ADU siting also follows the Marion County Rural Zoning Code, including the 100-foot accessory-building setback near farm or forest land. Confirm zone and UGB status with the Marion County or your city planning office.

Violations & Fines

Building an ADU without the required land-use and building permits is a code violation enforced by the county or city planning and building department, with stop-work orders, permit-after-the-fact requirements, or removal. Standards vary by jurisdiction.

Frequently Asked Questions

Does Marion County allow ADUs?

Yes. Oregon's ORS 197.312(5) requires the county and its cities to allow at least one ADU per detached single-family home in urban-growth-boundary residential zones, subject to reasonable siting and design rules.

Can they require me to live on-site or add parking?

No. State law says reasonable local ADU regulations cannot include owner-occupancy requirements of either the primary or accessory structure, or a requirement to build additional off-street parking.

Sources & Official References

Other rules in Marion County

Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions Parking Rules: Curb Color RulesSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Driveway RulesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions

All Marion County rules

How Marion County compares: Easiest Cities to Build an ADU·Compare Marion County to another location·View the Oregon accessory structures overview

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ADU Rules in Cities Across Marion County

Salem, OR