Looking for cost of accessory dwelling unit in Seattle, WA? Call AccessoryDwellingUnit Services for a contact a provider — no obligation. Licensed adu builders serve Seattle 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 involves several moving parts that shape your total investment. The final figure depends heavily on whether you choose a prefab unit or a custom build from the ground up. Site conditions are another major factor; if your property requires extensive grading, utility trenching, or foundation work, costs will climb. You also have to consider your choice of finishes, like high-end appliances or custom cabinetry. Navigating local permit fees and impact assessments also adds to the total.

About this service

Building an ADU involves several variables that shift the total investment. Your site conditions, the type of foundation, and the quality of finishes you choose will dictate whether you land on the lower or higher end of the spectrum. Because every lot is unique, we provide a breakdown of your specific project requirements to ensure full transparency. Exact pricing confirmed free on the call.

Frequently asked in Seattle

What are the disadvantages of ADUs?

Potential disadvantages of ADUs include the initial construction costs and the possibility of reducing your existing yard space. You should also consider any impacts on utilities and privacy. Thorough planning is key to addressing these concerns effectively.

How much does an ADU cost in Washington?

What are the rules for ADUs in Washington?

Washington state has ADU-friendly laws, but Seattle has its own specific zoning regulations regarding size, setbacks, height, and parking requirements. Understanding these local rules is crucial for a successful ADU project. We can help clarify these for your situation.

Is ADU allowed in Maryland?

Our services are focused on accessory dwelling units within Washington state, specifically in the Seattle area. If you require information about ADUs in Maryland, you will need to consult local resources and professionals familiar with Maryland's specific regulations.

Washington state does not have a direct statewide grant of that amount. However, we can explore potential financing options or local incentives that might be available for your Seattle ADU project.

Can I build an ADU on my property?

Eligibility for an ADU in Seattle depends on your property's zoning, lot size, and existing structures. The city has specific requirements for setbacks, height, and density. A preliminary discussion can help assess your property's suitability for an ADU.

Also serving nearby: Kirkland · Bellevue · Renton · Kent · Federal Way

All cities in Washington →

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

Service area details

755,078residents

8,989per sq mile

8ZIP codes served

Serving all of Seattle — population 755,078; about 8,989 residents per square mile across 84.0 sq mi. ZIP codes covered include 98101, 98102, 98103, 98104, 98105, 98106, 98107, 98108.

Neighborhoods served in Seattle: Ballard, Capitol Hill, West Seattle, Fremont, Phinney Ridge — and every surrounding area.