ADU (accessory dwelling unit) Cost in Oregon: Home Prices, Site Costs, SDCs, and Portland

These are Wolf’s published planning prices for Oregon. Agency charges, local design standards, utility work, and access vary by property. Check the applicable ADU size calculation before selecting a model; the Portland rule also considers the size of the main dwelling.

The table above uses the same pricing information as our FAQ page. A complete project price still requires a property-specific scope.

What the planning prices cover

The Model B starts at $67,500 for the home itself and is available only in the City of Portland. Oregon BCD inspects the structure as a prefabricated building; your city or county still reviews the foundation, placement, and utilities. Installation and appliances are separate. You can purchase our appliance package or provide your own.

Your complete project is quoted for your property. The written proposal defines what is covered, including required site work, utility connections, permits, delivery, installation, and any separate taxes, appliances or selections.

Permitting and agency fees are confirmed for your project. Ask the agencies for an itemized estimate, including SDCs and any connection charges. ORS 197A.425 establishes an ADU allowance in qualifying urban areas; it does not eliminate project fees. Rural county programs have separate eligibility rules.

Installation is quoted after a property review. The scope can include excavation, foundation, utility trenching, delivery, placement, connections, and final inspection. Your proposal confirms the work for your address, including any longer trench, well or septic work, electrical upgrades, or delivery requirements.

Portland has its own size rule

Inside Portland city limits, the standard detached-ADU size limit is 800 square feet or 75 percent of the living area of the main dwelling, whichever is less. Match the model to that calculation and the property’s other development standards. Portland Permitting & Development handles building review through DevHub, with other bureaus reviewing applicable utilities and site work.

Portland’s ADU SDC waiver under Code 17.14.070 F requires a recorded ten-year covenant restricting short-term rentals on the property, including the primary dwelling. It does not waive every project charge. Other housing programs have separate requirements; confirm the applicable program and intended use before counting savings. See the Oregon rules guide for the linked city code and current waiver instructions.

Gresham, Milwaukie, Beaverton, and Oregon City each set their own SDC schedule, and Portland’s 800 sq ft limit doesn’t apply there.

What still varies by lot

• Stormwater. Whether you can infiltrate on site or need a legal connection can change the budget significantly.
• Trees. A backyard that looks open on paper can shrink once the arborist maps protected root zones.
• Electrical service and utility laterals. Wolf homes are all-electric. An existing 100-amp service may need an upgrade before it can support a second dwelling.
• Access. Narrow streets, parked cars, and a tree in the crane’s swing path affect delivery more than distance from the factory does.

Factory construction makes the home price more predictable than a site-built project, but Portland utility and development charges still apply. See the Oregon ADU rules guide for statewide requirements, then send us the property address for a project-specific estimate.

Compare methods on prefab ADU vs stick-built. If you are looking at a Portland–Vancouver design-build shop, read Wolf vs MyADU.