Polk County, OR ADU (accessory dwelling unit) Rules: Urban and Rural Site Checks

Oregon law sets a statewide ADU framework, but in Polk County the details come from the county’s Chapter 118, which sets county-level standards for accessory dwelling units in areas where that chapter applies.

Polk County adopted Ordinance 26-01 on June 17, 2026 with immediate effect. Chapter 118 now separates an urban path under section 118.030 from a rural path under section 118.040. Older summaries that cover only the urban rules are out of date.

Official starting point: Polk County Zoning Ordinance.

Inside an urban growth boundary

For county-administered properties, section 118.030 lists SR, AR-5, AR-10, AF-10, and RS zones. With a qualifying primary dwelling, the urban standards include:

• One ADU is allowed for each detached single-family dwelling.
• The ADU cannot exceed 900 square feet or 75 percent of the main dwelling’s total floor area, whichever is less.
• A detached ADU has a maximum height of 25 feet.
• The ADU may not be a manufactured dwelling.
• It must comply with state building code requirements for a residence.
• Main-dwelling development standards apply unless the ADU section specifies otherwise.
• The section addresses an approved septic repair area or location within 300 feet of a sanitary sewer line. Proximity alone does not establish approved connection capacity.
• Detached ADUs are not allowed in a front yard area.

The 2026 amendment changed the former “perimeter area” wording to total floor area. Confirm the calculation before choosing a model.

Outside an urban growth boundary

The adopted rural program covers SR, AR-5, AR-10, AF-10, and GR/LDR zones. Screening conditions include an existing single-family dwelling, at least two acres, no more than 900 square feet of usable floor area, and placement within 100 feet of the existing home.

The ordinance requires wastewater compliance and addresses restricted groundwater use. Owners must coordinate an evacuation plan and staging area with the fire district. Vacation occupancy is prohibited, and the ADU cannot be divided onto a separate parcel or followed by another ADU on that parcel.

Confirm the full criteria in section 118.040, the underlying zone, and applicable overlays before choosing a layout. The adoption findings identify water availability as a practical constraint. An eligible zone does not guarantee a new water connection or adequate well supply.

A connection to an approved existing septic system and a new system are different estimating scopes. Establish permitted capacity and any repair area before locating the ADU, driveway, or patio.

City limits can change the process

Polk County includes Dallas, Monmouth, Independence, parts of Salem, and smaller communities. If your property is inside a city, the city may control the local permit path. The county chapter is still useful context, but the city counter may be the actual authority for your address. We confirm jurisdiction before we talk about models.

Manufactured, modular, and site-built are not the same thing

Polk County’s urban section 118.030 retains a restriction on manufactured dwellings. That does not automatically rule out a modular home built to residential code through Oregon’s prefabricated-structure process. But it does mean the housing type, state approval path, foundation, and local placement details need to be clear.

Wolf builds modular homes in a factory, not HUD code (the federal standard for manufactured homes) manufactured homes. For Oregon projects, the structure goes through the state modular path, then the local jurisdiction reviews site placement, foundation, setbacks, utility connections, and inspections.

What Wolf checks first

For a Polk County ADU, we want to know:

1. Is the property inside a city, inside a UGB, or rural?
2. What zoning applies?
3. Is there an existing detached single-family dwelling?
4. What is the primary dwelling’s total floor area for an urban application, or the parcel acreage for a rural application?
5. Is the site served by sewer, or does septic capacity need review?
6. Does the location meet the applicable urban or rural siting rules and provide workable delivery access?
7. Which model stays inside the local size and height envelope?

Start with a property address

If you are looking at Dallas, Monmouth, Independence, Salem-area Polk County, or an unincorporated property, send us the address and the goal for the ADU. We will help identify the jurisdiction, the likely constraints, and the Wolf models that deserve a closer look.

For the statewide background, read our Oregon ADU rules guide. For model dimensions and pricing, compare all Wolf models.

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