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.

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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.

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

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Privacy Policy

Last updated: June 3, 2026

This Privacy Policy describes how Prolific Solutions NW (Washington L&I #PROLISN776L6, UBI 604 750 488) collects, uses, and protects information from our customers and subcontractors.

Information We Collect

We collect contact information (name, email, mobile phone number, mailing address) and project information (property address, scope of work, photos, signed agreements) from customers who request our services. We collect equivalent information from subcontractors who enter into a Master Subcontractor Agreement with us.

How We Use Your Information

We use the information you provide solely to deliver the services you engaged us for: scheduling, project coordination, document delivery via secure portals, billing and payment processing, and operational communications including SMS notifications as described below. We do not sell or rent your personal information.

SMS / Text Messaging

We collect mobile phone numbers from customers and subcontractors solely to deliver transactional SMS messages related to active projects, signed agreements, and operational notifications. We do not share, sell, rent, or distribute mobile numbers or SMS message content to any third party. SMS metadata (delivery status, opt-out events) is retained only to comply with carrier opt-out rules and to provide customer service. You can opt out at any time by replying STOP to any SMS from us, or by contacting (425) 800-4775. Full SMS terms: prolificsolutionsnw.com/sms-terms.

Third-Party Sharing

We share your information only with vendors and service providers that help us deliver our services (such as scheduling and accounting software, payment processors, and licensed subcontractors assigned to your project). We require these parties to handle your information consistent with this policy. We do not sell your information.

Data Retention

We retain customer records for the duration required to fulfill our contractual and legal obligations (including warranty periods, tax records, and Washington L&I compliance). You can request deletion of records not subject to retention requirements by emailing info@prolificsolutionsnw.com.

Your Rights

You can request access to, correction of, or deletion of your personal information by contacting us at info@prolificsolutionsnw.com or (425) 800-4775. We will respond within 30 days.

Contact

Prolific Solutions NW
Email: info@prolificsolutionsnw.com
Phone: (425) 800-4775
WA L&I PROLISN776L6 · UBI 604 750 488

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.

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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.

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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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