Accessory dwelling unit cost — Federal Way, WA
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
Total costs for an ADU vary based on the size of the unit, the complexity of the site, and the quality of materials you select for the kitchen and bathroom. Things like trenching for new sewer lines or upgrading your main electrical panel can also impact the bottom line. We provide an exact pricing confirmed free on the call.
Frequently asked in Federal Way
Who is an accessory dwelling unit contractor in Federal Way?
How do I get an ADU permit in Federal Way?
Where can I find an ADU near me in Federal Way?
What are the options for an accessory dwelling unit rental in Federal Way?
Where can I find accessory dwelling unit builders in Federal Way?
What are some accessory dwelling unit companies in Federal Way?
What are the considerations for a detached accessory dwelling unit in Federal Way?
Also serving nearby: Tacoma · Kent · Renton · Seattle · Bellevue
More on this: HUD ADU resources — ADU policy and financing research.
Service area details
Serving all of Federal Way — population 97,701; about 4,375 residents per square mile across 22.3 sq mi. ZIP codes covered include 98003, 98023, 98063, 98093.
Neighborhoods served in Federal Way: Lake Dolloff, The Commons, Midway, Miracle, Woodmont — and every surrounding area.
Areas we serve
Browse by state, then city.