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

In Yamhill County, whether you can build an ADU depends mostly on whether your property sits inside or outside an Urban Growth Boundary (UGB), and on the zoning that applies to your specific parcel. An accessory dwelling unit that is straightforward on a residential lot inside a UGB can carry stricter standards on rural land outside one.

Start by confirming the property’s zone and which jurisdiction reviews it. Inside McMinnville or Newberg city limits, the city reviews the ADU under its own code. The county rules below apply where Yamhill County is the reviewer.

Where ADUs are allowed

Yamhill County allows ADUs both inside and outside Urban Growth Boundaries, including in certain rural residential situations. The standards become more restrictive outside a UGB, and additional restrictions can apply if the property is adjacent to forestry or farmland resource zones.

A few foundational rules apply broadly:

• Only one ADU is allowed per principal single-family dwelling.
• An ADU can be detached, attached, interior to the home, or located within part of a detached accessory building.
• A recreational vehicle cannot be used as an ADU.

The rural ADU path (outside a UGB)

Outside an Urban Growth Boundary, the county’s thresholds are tighter:

• The parcel must be at least two acres and outside an urban reserve.
• The ADU must be located no farther than 100 feet from the existing single-family dwelling.
• Outside a UGB, the ADU may also need to meet additional wildfire-related and resource-zone setback requirements.

A parcel can clear all three and still need more work on access, utilities, and site-specific constraints.

Size limits

Section 1014.02 sets the smaller of 900 square feet or 75% of the primary dwelling’s floor area for detached and attached units. It includes a whole-floor conversion provision, but the ordinary rural path is also subject to the state 900-square-foot usable-floor-area ceiling. Do not assume an urban conversion exception permits a larger new rural ADU.

Setbacks and height

Section 1014.02 limits detached height to the smaller of 25 feet or the primary dwelling’s height. Confirm zone setbacks and applicable resource-land buffers with Planning. The posted section contains older wildfire-map references; have the county identify the currently applicable fire and building provisions for your application.

Water, septic, and sewer

The rural section calls for the same water source or supply system as the existing dwelling, subject to lawful use and groundwater restrictions. An ADU application must also establish wastewater compliance. Confirm the source, permitted demand, and system capacity before locating the home or estimating connection work.

Driveway and access

If possible, the ADU should use the same driveway as the primary dwelling.

Rental rules

Short-term rental use of the ADU is prohibited. The county section defines this as paid occupancy for fewer than 30 consecutive days. Confirm the full intended-use requirements with the permit reviewer before relying on rental income.

Permit process

Yamhill County requires an ADU application with supporting materials. These generally include applicant and property-owner details, tax lot and zoning information, the square footage of the proposed ADU and primary dwelling, a site plan showing property lines, setbacks, buildings, and access, a floor plan for the proposed ADU, and a written explanation of how the proposal complies with county standards, including how water and wastewater will be handled.

The relevant code references for ADUs in the county include:

• Yamhill County Zoning Ordinance Section 1014, Accessory Dwelling Units
• Section 502, Very Low Density Residential Districts
• Section 401, Forestry District F-80

Which sections govern your project depends on your parcel’s zoning.

What Wolf checks first

For a Yamhill County project, we usually want to know:

1. Is the parcel inside or outside a UGB?
2. What zoning applies, and which code section governs the ADU?
3. Is there an existing single-family dwelling on the property?
4. For rural parcels: is the lot at least two acres, and can the ADU sit within 100 feet of the existing home?
5. Can the property support the ADU’s water and wastewater needs?
6. Do wildfire or resource-zone setbacks apply, and can the unit be delivered and set safely?

Modular homes in Yamhill County

Wolf has built more than 650 modular homes and ADUs across the Pacific Northwest. The structure side and the property side of a project are handled differently: the home itself is one part of the approval, while the property still needs local placement, foundation, utility, and inspection approvals. Yamhill County still approves the site-specific pieces. Confirm the exact review path for your project with Yamhill County and the State of Oregon.

Start with the address

If you are planning an ADU in Yamhill County, send us the property address and intended use. We will start with jurisdiction, zoning, Urban Growth Boundary status, utilities, and the models that fit the property.

Get a free Wolf property evaluation to find out what the parcel can support.

This is general information, not legal advice. Confirm current rules, fees, and application requirements with Yamhill County before you build.