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

In Wasco County, whether you can build an ADU depends heavily on where your parcel sits. The county’s rural ADU program applies only to specific zones, leaves out large areas including the National Scenic Area, and attaches conditions that depend on the property and intended use. Confirm current requirements with the Planning Division before choosing a design or budget.

Where ADUs are allowed in Wasco County

The county allows accessory dwelling units in a defined list of rural residential zones:

• R-R (2)
• R-R (5)
• R-R (10)
• TV-R
• WAM R-2
• WAM R-5

ADUs are not allowed in farm, forest, commercial, industrial, or other nonqualifying zones. They are also not allowed in the National Scenic Area or in resource zones.

In Wasco County, a parcel that looks rural and residential can still be ineligible for a rural ADU if it falls inside the National Scenic Area or a resource zone. Confirm scenic-area status for your address early.

Threshold conditions: lot, dwelling, and distance

Even within a qualifying zone, the county’s rural ADU path has threshold conditions that should be checked first:

• The parcel must be two acres or greater.
• There must be one existing single-family dwelling on the lot.
• The ADU is limited to 900 square feet.
• The ADU must be located no farther than 100 feet from the existing home.
• No more than one accessory dwelling unit is allowed per parcel.
• The parcel cannot be subdivided to separate the ADU from the primary dwelling.

A property can meet all of these and still need more work on access, septic, and wildfire mitigation.

Fire protection and defensible space

The property must be served by a structural fire protection service provider and meet applicable fire and access standards. The application asks about nuisance orders and pending actions; an informal complaint is not the same condition. Its older wildfire-map references need confirmation against current state and county requirements.

On rural parcels, fire service and defensible space often decide feasibility, so confirm them early.

Water, septic, and wastewater

The county application calls for the same water source or system as the existing dwelling and checks restricted-well conditions, along with water, sanitation, and wastewater compliance. It asks for health-district authorization to modify an existing waste system or a site evaluation showing that a new system is feasible. Septic capacity and water are part of eligibility, so check them before design.

Rental and occupancy rules

A rural ADU in Wasco County cannot be used for short-term vacation rental or occupancy. The deed restriction language in the application states that the ADU shall not, in perpetuity, be used for vacation occupancy.

If your goal is a short-term rental, review the rental rules before making a plan. Current county guidance does not identify a general owner-occupancy requirement, but confirm that point for your property.

Permit process

Start with the Planning Division and the ADU application. Have staff identify the review type, current criteria, and permit sequence for the proposed modular home. A HUD (the federal standard for manufactured homes)-manufactured-home inspection list is not a substitute for the selected modular home’s state and local approval requirements.

Use the current Wasco County Land Use and Development Ordinance with the application. The housing project page preserves the 2025 adoption history; its old appeal-period notice is not a current application deadline.

Confirm permit fees, setbacks beyond the 100-foot distance to the existing home, height limits, and parking requirements directly with the county.

What Wolf checks first

For a Wasco County project, we usually want to confirm:

1. Is the parcel in a qualifying zone (R-R, TV-R, or WAM R), and is it outside the National Scenic Area and resource zones?
2. Is the lot two acres or greater, with one existing single-family dwelling?
3. Can the ADU fit within 900 square feet and within 100 feet of the existing home?
4. Is there structural fire protection service, and can the parcel meet defensible space standards?
5. Can the property support the ADU’s water and septic/wastewater needs?
6. Do your plans for the home fit the perpetual no-vacation-occupancy deed restriction?

We answer these before finish selections, because they decide whether the project can go ahead.

Start with the address

If you are planning an ADU in Wasco County, send us the property address and intended use. We will start with zoning, scenic-area status, acreage, the existing dwelling, fire access, septic, and model fit.

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

Ready to find out if your parcel qualifies? Get a free Wolf property evaluation and we will check the specifics for your address.

This is general information, not legal advice. Confirm current rules, fees, and application requirements with the Wasco County Planning Division.