Backyard accessory dwelling unit — Seattle, WA

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

A backyard ADU is a detached small home built on your property, separate from your main house. People typically build these to create extra living space for family members, as a private home office, or to gain additional rental income. Because they are freestanding, you will need to consider utility hookups, site access for crews, and local setback requirements. Costs vary based on the foundation type and utility connections. Exact pricing confirmed free on the call.

Frequently asked in Seattle

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

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

Service area details

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: Phinney Ridge, Ballard, Green Lake, Capitol Hill, Queen Anne — and every surrounding area.