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.

Trex vs. AZEK vs. Fiberon — Composite Decking Comparison (Seattle)

URL slug: /cost-guides/composite-decking-comparison/ Target keywords: composite decking comparison Seattle | Trex vs AZEK cost | best composite decking Pacific Northwest | Fiberon vs Trex


Composite decking has largely replaced pressure-treated wood as the material of choice for new decks in the Puget Sound. The main brands — Trex, AZEK, and Fiberon — each have a distinct product lineup, warranty structure, and price point. Here’s how they compare for homeowners in the Seattle metro.

The Three Main Composite Brands

Trex is the largest composite decking manufacturer in North America and the most widely specified by contractors in King County. Trex is made from 95% recycled wood and plastic film — it’s one of the most environmentally responsible products in the category. The main product lines, from entry-level to premium, are: Trex Select, Trex Enhance, and Trex Transcend.

AZEK (now part of the TimberTech brand family) is a PVC-based composite — it contains no wood fiber, which makes it more resistant to moisture and staining than wood-blended products. It’s the premium choice for homes close to water, like Puget Sound waterfront properties, where moisture exposure is highest.

Fiberon is a wood-polymer composite with good durability at a slightly lower price point than AZEK. It’s the value play among premium composites.

Cost Comparison — Installed, King County

Prices below reflect installed cost by a licensed contractor in King County, including framing, decking, a basic post railing, and permit. Not materials only.

ProductMaterial TierInstalled Cost (400 SF deck)
Trex SelectEntry$16,000–$21,000
Trex EnhanceMid$19,000–$25,000
Trex TranscendPremium$24,000–$32,000
AZEK Harvest / LandmarkEntry-Mid$22,000–$29,000
AZEK Arbor / VintagePremium$28,000–$38,000
Fiberon Good Life / PromenadeMid$18,000–$24,000

Costs vary by project complexity, site conditions, and current material pricing. Get a project-specific estimate from Prolific — free estimate here →

Warranty Comparison

BrandFade & StainStructuralNotes
Trex Transcend25 years25 yearsRequires certified contractor for full warranty
Trex Enhance25 years25 years
AZEK (TimberTech)30 years30 yearsNo-sand, no-stain guarantee
Fiberon Promenade25 years25 years

Which One Is Right for the Pacific Northwest?

The Puget Sound climate — high moisture, significant UV variation, pollen and debris — tests composite decking differently than drier climates. A few notes:

Moisture resistance: AZEK’s PVC core gives it the edge in high-moisture environments. If your deck is shaded, north-facing, or near the water, AZEK is worth the premium.

Heat retention: Dark composite colors can get hot in direct summer sun. Trex Transcend and AZEK both offer cooler-surface technology in their premium lines.

Mold and mildew: All three brands resist mold better than wood, but shaded decks in western Washington still benefit from periodic cleaning. AZEK requires the least maintenance.

As a Trex Pro certified contractor, Prolific can offer Trex’s full 25-year residential fade and stain warranty — only available through certified installers.

The Bottom Line

For most King County homeowners: Trex Enhance is the sweet spot — mid-range price, 25-year warranty, widely available locally. Go up to Trex Transcend or AZEK if you’re on or near the water, have a shaded north-facing deck, or are building a show deck before selling.

Get a composite deck estimate from Prolific →


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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

📋 Get a Free Estimate