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 Contracting: Why One Team Does It Better

Two Models, Very Different Experiences

When you’re planning a home renovation or restoration project, one of the most important decisions you’ll make isn’t about materials or finishes — it’s about how your project is managed. The two main approaches are design-build and traditional contracting (also called design-bid-build). Understanding the difference can save you time, money, and a lot of headaches.

At Prolific Design-Build and Restoration, we use the design-build model for every project — from kitchen remodels and bathroom renovations to full storm damage restorations and ADU construction. Here’s why, and what it means for you.

What Is Traditional Contracting?

In the traditional model, a homeowner hires separate companies for each phase. You might hire an architect or designer to create plans, then shop those plans to multiple general contractors for bids, then the winning contractor hires subcontractors for each trade (plumbing, electrical, framing, etc.).

The problem? Each party has their own timeline, budget, communication style, and priorities. The architect designs something beautiful but may not account for construction realities. The contractor bids based on the plans but finds issues during construction that require expensive change orders. The subcontractors work on their own schedules. And you, the homeowner, are stuck in the middle coordinating between all of them.

What Is Design-Build?

In the design-build model, one company handles everything — design, planning, permitting, construction, and project management. You have a single point of contact, a single contract, and a single team accountable for the entire project from concept to completion.

The design and construction teams work together from day one, which means designs are practical and buildable, budgets are realistic, and problems are solved before they become change orders.

Why Design-Build Delivers Better Results

Faster project timelines. In traditional contracting, design must be fully complete before construction bidding begins, and bidding takes weeks. In design-build, design and pre-construction planning overlap. This can shave weeks or months off your total project timeline.

Fewer change orders and budget surprises. Because the construction team is involved during design, they flag potential issues early — before they’re drawn into plans and before you’ve fallen in love with something that’s going to blow your budget. In traditional contracting, change orders are one of the biggest sources of cost overruns and homeowner frustration.

Single point of accountability. If something goes wrong in a traditional project, the architect blames the contractor, the contractor blames the subcontractor, and you’re left trying to figure out whose problem it is. In design-build, there’s one team responsible for everything. If there’s an issue, it’s on us to fix it.

Better communication. Instead of relaying messages between your designer, your contractor, and various subs, you talk to one project manager who knows every detail of your project. This alone reduces errors, delays, and misunderstandings dramatically.

Cost efficiency. Design-build projects consistently come in at lower total cost than traditional projects of similar scope. The elimination of the adversarial bidding process, reduced change orders, and streamlined communication all contribute to real savings.

Design-Build for Insurance Restoration

The design-build advantage is even more pronounced in insurance restoration projects. When your home has suffered water damage, fire damage, or storm damage, you don’t have time to separately hire an assessor, a mitigation company, and a reconstruction contractor. You need one team that can respond to the emergency, manage the insurance claim, perform the mitigation, and rebuild your home — all under one roof.

That’s exactly what we do at Prolific. From the first phone call through the final walkthrough, you work with one team. No gaps between mitigation and reconstruction. No finger-pointing between companies. No delays while you search for a builder after the emergency company finishes.

Questions to Ask Any Contractor

Whether you choose design-build or traditional, here are essential questions to ask before hiring:

Are you licensed and insured in Washington State? Do you handle design and construction, or will I need separate companies? Who will be my primary point of contact throughout the project? How do you handle change orders and unexpected issues? Do you have experience with insurance restoration claims? Can you provide references from recent projects similar to mine? What is your warranty on workmanship?

Experience the Design-Build Difference

Ready to see what one team managing your entire project feels like? Prolific Design-Build and Restoration offers free consultations for homeowners in Issaquah, Sammamish, Bellevue, Renton, and throughout King County.

Call (425) 800-4775 or request a free consultation. Black-owned and Latino-owned — one team, one vision, one standard of excellence.

Related: Kitchen Remodeling Guide | Bathroom Remodeling Guide | High-Value Home Restoration

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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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