Backyard 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
This is a detached unit built on your property, separate from your main home. It is a practical solution if you have extra yard space and want to add living quarters for family, guests, or tenants. These structures offer privacy while keeping you close to your primary residence.
Frequently asked in Federal Way
What's involved in ADU construction in Federal Way?
What are the different types of ADU units available in Federal Way?
How do I find local ADU services in Federal Way?
What does 'accessory dwelling unit' mean in Federal Way?
What are the accessory dwelling unit financing options in Federal Way?
What ADU companies serve the Federal Way area?
Where can I find an accessory dwelling unit near me 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, Chase Lake, Twin Lakes, Lake Dolloff, Brighton — and every surrounding area.
Areas we serve
Browse by state, then city.