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.

🏡

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.

How to Get a Building Permit in Renton, WA

Target keywords: Renton building permit | deck permit Renton WA | Renton building department | permit cost Renton


Renton has grown significantly over the past decade, and the city’s Building Division has kept pace with a modern online permit system and responsive staff. For homeowners in Renton — from the Highlands to Talbot Hill to Benson Hill — here’s what you need to know.

Does My Project Need a Permit in Renton?

Decks Attached decks require a permit. Detached decks over 200 SF or 30+ inches above grade require a permit.

Fences Fences up to 6 feet in rear and side yards are typically exempt. Front yard fences are subject to height limits (typically 4 feet maximum in front setback areas).

ADUs Renton allows both attached ADUs and detached accessory structures. Building permit required.

Interior Remodels Standard: structural, electrical, plumbing, and HVAC require permits.

Renton Permitting Department

City of Renton Building Division – Website: rentonwa.gov/building – Permit portal: https://permitting.rentonwa.gov – Phone: (425) 430-7200 – Address: 1055 S Grady Way, Renton, WA 98057

Renton has an online permit portal for submittal and inspection scheduling.

Permit Fees in Renton

ProjectEstimated Fee
Deck (200–400 SF)$400–$800
Fence (if required)$150–$350
ADU$2,000–$5,500+
Kitchen remodel (with plumbing)$600–$1,400
Room addition$1,200–$3,000

How Long Does Permitting Take in Renton?

  • Simple projects: 2–4 weeks
  • Standard residential: 5–12 weeks
  • Complex projects: 3–6 months

What Renton Inspectors Check

Renton inspectors pay close attention to setbacks, lot coverage limits, and stormwater drainage for exterior projects. The city has steep-slope regulations in the Highlands and Talbot Hill areas — exterior work near slopes may trigger geotechnical review.

Let Prolific Handle the Permits

Prolific pulls permits for every project we build — no permitting headaches for you. Get an estimate →


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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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