Accessory dwelling unit contractor

Looking for accessory dwelling unit contractor 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

A contractor oversees the physical build, managing the subcontractors, materials, and daily construction progress. They are responsible for making sure the structure is built according to the approved plans and local safety standards. You need a contractor when you have your designs finalized and are ready for the actual building phase to begin. They act as the primary point of contact for all site activity.

Frequently asked in Seattle

What are the disadvantages of ADUs in Seattle?

The main disadvantages might include the initial construction cost and potential impacts on your existing yard space. You'll also want to consider any effect on property taxes and utility bills. However, the long-term benefits of increased rental income and property value are significant. Let's discuss your specific situation.

How much does an ADU cost in Washington?

What are the rules for ADUs in Washington?

Washington state has laws encouraging ADUs, and cities like Seattle have their own specific zoning ordinances and building codes. These typically cover lot size, setbacks, and occupancy standards to ensure ADUs integrate well into neighborhoods. Understanding these local regulations is essential for a successful build. We can help clarify them for you.

Is an ADU allowed in my Seattle neighborhood?

Washington may have different state or local programs, or financing options, available for ADU construction. We can help you explore what might be applicable for your project in Seattle. Let's discuss your needs.

Can I build an ADU on a steep hillside in Seattle?

Building an ADU on a steep hillside in Seattle requires specialized engineering and design to ensure structural integrity and compliance with city codes. Areas like Magnolia present unique challenges. The pros we partner with have experience with these complex sites. They can assess your property's suitability.

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, Queen Anne — and every surrounding area.