Detached accessory dwelling unit — 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
A detached ADU is a standalone building separate from your main house, like a cottage or a converted garage. You choose this style if you want maximum privacy for your tenants or family members. Because it requires its own foundation and utility lines, it is a significant construction project. Exact pricing confirmed free on the call.
Frequently asked in Federal Way
What is the accessory dwelling unit cost in Federal Way?
What are the accessory dwelling unit permit costs in Federal Way?
Where can I find an ADU company in Federal Way?
What are 24-hour ADU services in Federal Way?
Are prefabricated accessory dwelling units a good option in Federal Way?
What are the accessory dwelling unit permit requirements in Federal Way?
What are accessory dwelling unit rules in Massachusetts?
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: Twin Lakes, Dash Point, West Campus, Woodmont, Mirror Lake — and every surrounding area.
Areas we serve
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