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.

Transforming Spaces: Construction Contracting for All Your Needs

The Art of Construction Contracting

When it comes to transforming spaces, construction contracting is the art that brings dreams to life. Whether you’re planning to build a new home, renovate your office, or add an extension to your existing property, a reliable construction contractor is your key to success.

At our construction contracting company, we understand that each project is unique and requires a personalized approach. We take pride in our ability to offer comprehensive services that cater to all your needs, ensuring a seamless construction process from start to finish.

Quality Craftsmanship and Attention to Detail

When you choose our construction contracting services, you can expect nothing but the highest quality craftsmanship and attention to detail. Our team of skilled professionals is experienced in handling a wide range of construction projects, from residential to commercial.

We believe that every detail matters, no matter how small. From the foundation to the finishing touches, we strive for perfection in every aspect of our work. Our commitment to excellence ensures that your project is completed to the highest standards, surpassing your expectations.

Exceptional Service and Customer Satisfaction

Customer satisfaction is at the heart of what we do. We understand that embarking on a construction project can be a daunting task, which is why we are dedicated to providing exceptional service and support throughout the entire process.

From the moment you contact us to discuss your project, our team will work closely with you to understand your vision and goals. We will guide you through the various stages of construction, offering professional advice and expertise along the way. Our goal is to make the journey as smooth as possible, ensuring your complete satisfaction.

Transforming Dreams into Reality

With our construction contracting services, the possibilities are limitless. Whether you have a specific design in mind or need help envisioning the perfect space, our team of experts is here to turn your dreams into reality.

From concept to completion, we will be by your side, ensuring that every detail is executed with precision and care. Our commitment to excellence and customer satisfaction sets us apart in the industry, making us the go-to choice for all your construction needs.

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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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