Cost to build accessory dwelling unit

Looking for cost to build accessory dwelling unit in Portland, OR? Call AccessoryDwellingUnit Pros for a contact a provider — no obligation. Licensed adu builders serve Portland and the surrounding area, and you'll get straight answers on timing and what affects the price.

Last updated: September 24, 2026

What affects the price

Building an ADU is a custom project, so costs vary based on your specific choices. Site conditions are the biggest factor; if your land requires significant grading, utility extensions, or foundation work, those expenses add up quickly. Choosing high-end finishes, custom cabinetry, or complex roof lines will also push the budget higher compared to a standard design. Prefabricated units often offer predictable costs, while custom site-built structures allow for more flexibility but can be harder to estimate upfront. Exact pricing confirmed free on the call.

About this service

Determining the cost requires looking at site preparation, foundation work, and the level of interior finishing you choose. Costs change based on whether you opt for a pre-designed layout or custom architecture. You should research these costs when you are ready to evaluate the financial return of your property upgrade. Exact pricing confirmed free on the call.

Frequently asked in Portland

What are the disadvantages of ADUs in Portland?

How much does an ADU cost in Oregon?

What are the rules for ADUs in California?

California has state laws that facilitate ADU construction, but local cities retain the ability to implement their own specific zoning ordinances. These often cover aspects like lot coverage, setbacks, and parking requirements. It's crucial to consult local building departments. We can help you find specialists.

Is an ADU allowed in Maryland?

What are the rules for ADU in California?

California has offered grants to make ADU construction more affordable, particularly for low-income households. These programs have specific eligibility requirements and application processes. The pros can help you explore if similar funding opportunities are available in your region.

Also serving nearby: Vancouver · Beaverton · Gresham · Hillsboro · Salem

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More on this: HUD ADU resources — ADU policy and financing research.

Service area details

630,498residents

4,723per sq mile

8ZIP codes served

Serving all of Portland — population 630,498; about 4,723 residents per square mile across 133.5 sq mi. ZIP codes covered include 97201, 97202, 97203, 97204, 97205, 97206, 97207, 97208.

Neighborhoods served in Portland: Alberta Arts District, Sellwood-Moreland, Pearl District, Downtown, Hawthorne, Laurelhurst — and every surrounding area.