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.

Design-Build vs. Traditional Contractor: Which Is Right for Your King County Renovation?

Understanding the Design-Build Advantage

If you’re planning a renovation, addition, or major repair on your King County home, you’ll face a fundamental choice: hire a traditional contractor and separate designer, or work with a design-build firm that handles both under one roof. As a design-build contractor ourselves, we’ll give you the honest pros and cons of both approaches.

The Traditional Model: Architect + Contractor

In the traditional model, you hire an architect or designer to create plans, then bid those plans out to general contractors for construction. This approach gives you maximum design flexibility and the ability to shop competitive bids. However, it comes with significant drawbacks that become apparent during the project.

Communication gaps between designer and builder are common — what looks great on paper may be impractical or prohibitively expensive to build. Change orders pile up when construction reality doesn’t match design assumptions. The timeline extends because design must be fully completed before construction can begin. And when problems arise, you’re caught between two parties who may disagree on responsibility.

The Design-Build Model: One Team, One Contract

Design-build consolidates design and construction under one company, one contract, and one point of accountability. Your design team works alongside your construction team from day one, which means designs are buildable from the start, cost estimates are accurate because the people pricing the work are the same people doing it, the timeline compresses because design and pre-construction can overlap, and there’s no finger-pointing when issues arise — one company owns the entire outcome.

Why Design-Build Makes Special Sense for Restoration

Here’s where our perspective as a restoration + design-build firm gives us unique insight. When your home suffers damage — whether from water, fire, storm, or mold — you’re not just repairing. You’re often rebuilding entire rooms, and many homeowners use this as an opportunity to upgrade.

In the traditional model, you’d need a restoration company for the cleanup, then an architect to redesign, then a contractor to rebuild. That’s three companies, three contracts, three timelines, and three parties for your insurance company to coordinate with. With Prolific’s design-build model, one team handles the entire journey from damage assessment through design and final construction — and your insurance company has one contractor to work with.

Cost Comparison

Design-build projects typically cost 6-12% less than traditional delivery for equivalent scope. The savings come from eliminated redesign costs, fewer change orders, compressed timelines that reduce general conditions costs, and integrated value engineering where the builder optimizes the design for cost without sacrificing quality.

For insurance restoration projects specifically, the savings can be even greater because the streamlined process reduces additional living expenses (ALE) by getting you back into your home faster.

When Traditional Might Be Better

If you’re building a custom architectural statement — a home where the design itself is the primary value — the traditional architect-led model may serve you better. For most residential renovations, additions, restorations, and remodels in King County, however, design-build offers better value, faster delivery, and less stress.

Ready to Explore Design-Build?

Prolific Design-Build and Restoration offers free design consultations for King County homeowners. Whether you’re recovering from property damage or planning an upgrade, we’ll show you what’s possible with an integrated design-build approach. Call (425) 800-4775 or visit our contact page to schedule your consultation.

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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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