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.

Mold in Your King County Home? Here’s What You Need to Know

Understanding Mold in Pacific Northwest Homes

Living in King County means living with moisture. Our region averages 152 rainy days per year, and that persistent dampness creates ideal conditions for mold growth — especially in the hidden spaces of your home like crawlspaces, behind walls, under sinks, and in attics.

At Prolific Design-Build and Restoration, mold remediation is one of our most common service calls. Here’s what every King County homeowner should know about mold — the risks, the signs, and the solutions.

Why Mold Is More Than a Cosmetic Problem

Mold isn’t just unsightly — it’s a health hazard and a structural threat. Common household molds like Cladosporium, Aspergillus, and the more dangerous Stachybotrys (black mold) can cause respiratory issues, allergic reactions, headaches, and chronic fatigue. Children, elderly residents, and anyone with respiratory conditions are especially vulnerable.

Structurally, mold breaks down organic materials — wood framing, drywall paper, insulation, and carpet backing. Left unchecked, mold can compromise structural integrity and cause damage far exceeding the cost of early remediation.

Signs You May Have a Mold Problem

Not all mold is visible. Watch for these warning signs: persistent musty or earthy odors (especially in basements, bathrooms, or crawlspaces), visible discoloration on walls, ceilings, or grout, condensation on windows or pipes, recent water damage that wasn’t professionally dried, unexplained allergy symptoms that worsen at home, and warping or bubbling of paint, wallpaper, or flooring.

If you notice any of these signs, don’t wait. Mold colonies can double in size every 24-48 hours under favorable conditions, and King County’s climate provides those conditions most of the year.

The Mold Remediation Process

Professional mold remediation follows a proven protocol. It starts with a thorough assessment including air quality testing to identify mold types and concentration levels. Then the affected area is isolated with physical containment barriers and negative air pressure to prevent spore spread during removal.

Contaminated materials are safely removed — this often includes drywall, insulation, carpet, and sometimes structural members depending on the severity. Remaining surfaces are treated with antimicrobial agents, and the air is filtered using HEPA filtration until post-remediation testing confirms safe levels.

Here’s where Prolific’s design-build advantage matters: after remediation, most contractors leave you with a stripped-down space and a recommendation to \”call a builder.\” We handle the entire rebuild in-house — new drywall, insulation, flooring, paint, and any structural repairs. One contractor, one timeline, one point of contact.

Does Insurance Cover Mold Remediation?

The answer depends on the cause. Mold resulting from a covered peril — like a burst pipe or storm damage — is typically covered under your homeowner’s insurance. Mold from long-term moisture issues, maintenance neglect, or gradual leaks is usually excluded.

The key is connecting the mold to a sudden, accidental event. Prolific’s documentation process is designed to establish this connection clearly, giving your insurance claim the best chance of approval. We photograph the water source, document the timeline, and create Xactimate estimates that adjusters recognize and accept.

Preventing Mold in Your King County Home

Prevention starts with moisture control. Keep indoor humidity below 50% (use a hygrometer to monitor), ensure your home has adequate ventilation — especially in bathrooms and kitchens, fix any leaks immediately no matter how small, maintain your gutters and downspouts, and have your crawlspace inspected annually for moisture issues.

If you suspect mold in your King County home, call Prolific Design-Build and Restoration at (425) 800-4775. We provide free mold assessments and can have a remediation crew on-site within 24 hours.

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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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