ADU & DADU Contractor — King County, WA
From permit application to final walkthrough — Prolific handles design-build ADU and DADU projects across Federal Way, Issaquah, Renton, Kent, and greater King County.
Every ADU project is custom-designed for your lot, your goals, and King County code.
A standalone dwelling in your backyard. Most flexible for rental or multigenerational living. Requires setback compliance and separate utility connections.
Connected to the primary home via a shared wall. Lower cost than detached, faster permitting. Ideal for in-law suites or long-term rental income.
Converted from existing interior space — garage, basement, or bonus room. Lowest cost entry point. Limited to 500 sq ft per King County code.
Prolific handles every step. Most homeowners have never pulled a permit — we've done hundreds.
We verify your parcel's zoning, setbacks, lot coverage, and utility capacity before design starts. Catches 80% of project-killers on day one.
Architectural plans drawn to King County standards. Structural engineering included where required. Typical design phase: 3–6 weeks.
We submit to King County DPER or the applicable city (Federal Way, Renton, Issaquah, Kent). Electronic submission with full plan set.
County review typically takes 6–12 weeks. We respond to all correction requests and manage the back-and-forth until permit issuance.
Construction with milestone inspections. Final inspection and certificate of occupancy required before the unit can be rented or occupied.
Rough estimates — every project varies by site, size, and finish level. Free estimate available after a site visit.
| ADU Type | Size Range | Typical Cost Range |
|---|---|---|
| Junior ADU (JADU) | Up to 500 sq ft | $60,000 – $120,000 |
| Attached ADU | 400–800 sq ft | $120,000 – $200,000 |
| Detached ADU (DADU) | 400–1,200 sq ft | $160,000 – $320,000 |
Free site consultation. We'll tell you what's possible on your lot before you spend a dollar.
Get Your Free ADU EstimateProlific's Differentiator
Most contractors patch the damage and leave. We use the restoration as a launchpad — pairing insurance coverage with a remodel that upgrades what you had.
Insurance covered the roof and siding. While we had the crew on-site, the homeowners financed a kitchen remodel they'd been putting off for years. One mobilization, two wins.
A burst pipe triggered an insurance claim for the subfloor and drywall. We rebuilt the bathroom larger than it was — same timeline, carrier paid the base, owner paid the delta.
Garage total loss became a permitted two-car garage with a studio ADU above. Insurance rebuilt what burned. The ADU now generates rental income to offset the mortgage.
7 questions to ask before hiring any contractor in King County — takes 2 minutes to read.
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Prolific Design-Build & Restoration — Federal Way, WA