ADU & DADU Contractor — King County, WA

Add a Legal Dwelling Unit
to Your King County Property

From permit application to final walkthrough — Prolific handles design-build ADU and DADU projects across Federal Way, Issaquah, Renton, Kent, and greater King County.

$180KAverage ADU Cost (King County)
6–12moTypical Timeline Permit to Move-In
$1,800+Monthly Rental Income Potential
3–5yrAverage ROI Payback Period

What We Build

Every ADU project is custom-designed for your lot, your goals, and King County code.

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Detached ADU (DADU)

A standalone dwelling in your backyard. Most flexible for rental or multigenerational living. Requires setback compliance and separate utility connections.

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Attached ADU

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.

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Junior ADU (JADU)

Converted from existing interior space — garage, basement, or bonus room. Lowest cost entry point. Limited to 500 sq ft per King County code.

The King County Permitting Process

Prolific handles every step. Most homeowners have never pulled a permit — we've done hundreds.

1

Site & Zoning Review

We verify your parcel's zoning, setbacks, lot coverage, and utility capacity before design starts. Catches 80% of project-killers on day one.

2

Design & Engineering

Architectural plans drawn to King County standards. Structural engineering included where required. Typical design phase: 3–6 weeks.

3

Permit Submission

We submit to King County DPER or the applicable city (Federal Way, Renton, Issaquah, Kent). Electronic submission with full plan set.

4

Review & Corrections

County review typically takes 6–12 weeks. We respond to all correction requests and manage the back-and-forth until permit issuance.

5

Build & Final Inspection

Construction with milestone inspections. Final inspection and certificate of occupancy required before the unit can be rented or occupied.

Cost Ranges for King County ADUs

Rough estimates — every project varies by site, size, and finish level. Free estimate available after a site visit.

ADU TypeSize RangeTypical Cost Range
Junior ADU (JADU)Up to 500 sq ft$60,000 – $120,000
Attached ADU400–800 sq ft$120,000 – $200,000
Detached ADU (DADU)400–1,200 sq ft$160,000 – $320,000

Ready to Add a Unit to Your Property?

Free site consultation. We'll tell you what's possible on your lot before you spend a dollar.

Get Your Free ADU Estimate

Prolific's Differentiator

While We're Restoring Your Home, Let's Make It Better Than Before

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.

Storm + Remodel

Federal Way — Hail Damage + Kitchen Upgrade

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.

Water + Addition

Renton — Burst Pipe + Primary Bath Expansion

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.

Fire + Rebuild

Issaquah — Garage Fire + ADU Conversion

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.

Insurance Claim? We Handle Everything.

Your Insurance Company Has Adjusters.
Now You Have Us.

STORM DAMAGE RESPONSEthousands more for homeowners just like you.

Why Hiring a Licensed General Contractor in King County Matters for Your Project

Hiring a general contractor for a home renovation or restoration project in King County is one of the most important decisions you’ll make as a homeowner. The difference between a licensed, experienced contractor and an unlicensed operator can mean the difference between a project that adds lasting value to your home and one that creates years of headaches.

What a General Contractor Actually Does

A general contractor serves as the single point of accountability for your entire project. They coordinate all trades — framing, electrical, plumbing, HVAC, drywall, painting, flooring — ensuring each phase completes on schedule and passes inspection. They pull permits with King County or your local municipality, manage the budget, and handle the inevitable surprises that come with any construction project.

For restoration projects — water damage, fire damage, storm repairs — a general contractor who also specializes in restoration brings an additional layer of expertise. They understand insurance claim processes, mitigation requirements, and the specific building science involved in restoring a structure to pre-loss condition.

Licensing Requirements in Washington State

Washington State requires all contractors performing work over $800 to hold a valid contractor license through the Department of Labor and Industries. This license ensures the contractor carries a surety bond and has current liability insurance. You can verify any contractor’s license at secure.lni.wa.gov/verify.

Beyond state licensing, King County requires permits for most structural, electrical, plumbing, and mechanical work. A licensed general contractor handles permit applications and coordinates inspections — something unlicensed operators typically skip, leaving you liable for code violations that surface when you try to sell your home.

Design-Build: The Modern Approach

The traditional model of hiring an architect to design your project and then a separate contractor to build it is giving way to design-build — where a single firm handles both design and construction. This approach eliminates the communication gaps and finger-pointing that occur when designers and builders operate independently. Changes are handled in real-time because the design team and construction team sit in the same office.

At Prolific Design-Build and Restoration, our design-build approach means your renovation or restoration project moves from concept to completion under one contract, one timeline, and one point of contact. Whether you’re remodeling a kitchen in Bellevue, restoring storm damage in Kent, or adding a home office in Kirkland, the process is seamless.

Questions to Ask Before Hiring

Before signing with any general contractor in King County, verify their Washington State contractor license number and check for complaints, confirm they carry general liability insurance and workers’ compensation coverage, ask for references from recent King County projects you can actually visit, get a detailed written estimate — not a verbal quote, understand their payment schedule and never pay more than 10% upfront (per Washington State law), and confirm they pull all required permits and schedule all inspections.

Ready to Start Your Project?

Prolific Design-Build and Restoration is a licensed general contractor serving all of King County. From design through final walkthrough, we handle every aspect of your renovation or restoration project. Call us at (425) 800-4775 to discuss your project.

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Dealing with storm damage? We're here — call now or submit your info and we'll call you within the hour.

We Got Your Request

We respond within 2 business hours — same day for emergencies.

A member of our team will reach out shortly to schedule your free estimate or inspection. Here's what to have ready when we call:

What to Have Ready

  • Photos of the damage or area of concern (phone photos are fine)
  • Your insurance carrier name and claim number (if applicable)
  • Best time and number to reach you
  • A rough idea of when the damage occurred or project timeline
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Prolific Design-Build & Restoration — Federal Way, WA

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