Accessory dwelling unit permit 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.
Frequently asked in Federal Way
What are prefab ADUs in Federal Way?
What does 'accessory dwelling unit' mean in Federal Way?
What are the best accessory dwelling units available in Federal Way?
What are prefabricated accessory dwelling units in Federal Way?
What is the ADU cost in Federal Way?
Are there accessory dwelling units for rent in Federal Way?
How do I find an ADU builder 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: Woodmont, Lakeland South, Dash Point, Mirror Lake — and every surrounding area.
Areas we serve
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