Accessory dwelling unit construction 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
The cost to build an ADU depends on factors like your foundation type, utility connection distances, interior finish choices, and whether you are doing a detached build or a garage conversion. We provide an exact pricing confirmed free on the call.
Frequently asked in Federal Way
What is an ADU unit, and how does it apply to Federal Way?
An ADU unit is a secondary, independent living space on your property in Federal Way. Think of it as a small, self-contained home. It could be a detached structure or an addition to your existing house. Pros can help you determine the best ADU type for your Federal Way property, whether for rental income or family use.
What are accessory dwelling unit homes like in Federal Way?
Are there '24 hour ADU' services available in Federal Way?
How affordable are ADUs in Federal Way?
What about accessory dwelling unit new hampshire regulations for Federal Way?
Can I get an accessory dwelling unit contractor 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: Kenter Canyon, Lake Dolloff, The Springs, Woodmont, Mirror Lake — and every surrounding area.
Areas we serve
Browse by state, then city.