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.

Get a Free ADU Estimate (425) 800-4775
$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.

🏡

Detached ADU (DADU)

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

🏗

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.

🏠

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.

Tell Us What Happened — We'll Show You What's Possible
Insurance Claim? We Handle Everything.

Your Insurance Company Has Adjusters.
Now You Have Us.

STORM DAMAGE RESPONSEthousands more for homeowners just like you.

GET YOUR FREE CLAIM REVIEW → 📞 (425) 800-4775

Licensed & Insured · PROLISN776L6 · Serving All of King County

Facebook Instagram Twitter
Prolific Design-Build and Restoration logo - insurance restoration contractor King County WA
Get a Free Estimate

Build

Building More Space Shouldn’t Mean More Stress.

Whether you need an ADU for rental income, a garage conversion for a growing family, or structural additions that change how your home works — we handle the permits, the trades, and the timeline so you don’t have to.

What We Build

ADU / DADU Construction

Detached accessory dwelling units built to King County code. Perfect for rental income, multigenerational living, or a private home office. We handle permits through final inspection.

Garage Conversions

Transform underused garage space into livable square footage — bedrooms, studios, in-law suites. Insulation, electrical, plumbing, and finishes all included.

Structural Additions

Second-story additions, bump-outs, and room extensions. Engineered, permitted, and built to integrate seamlessly with your existing home.

Aging-in-Place Modifications

Barrier-free showers, wider doorways, stair lifts, and first-floor bedroom conversions. Stay in the home you love, safely and independently.

Permits, Trades, Timeline — We Handle It All

New construction in King County means permits, inspections, and coordinating multiple trades. We manage the entire process: architectural plans, permit applications, structural engineering, and every subcontractor on site. You get a single point of contact and a clear schedule from groundbreaking to move-in.

Permit Management
Licensed & Bonded
King County Code Compliant
Fixed-Price Proposals

How It Works

1

Site Visit & Feasibility

We visit your property, assess zoning and setback requirements, and confirm what’s buildable before you spend a dime on plans.

2

Plans, Permits & Proposal

Architectural drawings, engineering, permit submission, and a detailed fixed-price proposal. You know exactly what you’re getting and what it costs.

3

Build & Deliver

Foundation to finishes, we manage every phase. Regular progress updates, a clean jobsite, and a final walkthrough before handoff.

Ready to Add Square Footage That Pays for Itself?

ADUs in King County can generate $1,500–$2,500/month in rental income. Let’s talk about what’s possible on your lot.

Get a Free Estimate
(425) 800-4775

Licensed & Insured · PROLISN776L6 · Serving All of King County, WA

Commitment to Excellence

At Prolific Design-Build and Restoration, our background in the industry, combined with our mission-driven approach, sets us apart. Our team of dedicated professionals brings extensive experience and a passion for excellence to every project. We prioritize client satisfaction and believe in transparent, collaborative relationships.

Free Estimate

Facebook Instagram Twitter

© 2026 Prolific Design-Build and Restoration | All Rights Reserved

Get a Free Estimate
Get a Free Estimate

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
Back to Home

Prolific Design-Build & Restoration — Federal Way, WA

📋 Get a Free Estimate