Adu building — 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
Frequently asked in Federal Way
What's the cost to build an accessory dwelling unit in Federal Way?
What are the permit requirements for an ADU in Federal Way?
Where can I find an ADU near me in Federal Way?
What are the rules for accessory dwelling units in Washington State?
Can I build a modular ADU in Federal Way?
What is the cost of an accessory dwelling unit in Federal Way?
What are the benefits of accessory dwelling unit rental 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: Mirror Lake, Lake Holm, The Springs, Downtown Federal Way, Dash Point — and every surrounding area.
Areas we serve
Browse by state, then city.