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.

🏗

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.

James Hardie vs. LP SmartSide — Fiber Cement Siding Comparison

URL slug: /cost-guides/fiber-cement-siding-comparison/ Target keywords: fiber cement siding comparison Seattle | Hardie vs LP SmartSide | best siding Pacific Northwest | siding cost Seattle WA


Fiber cement siding has become the dominant exterior cladding material for home remodels and new construction in western Washington. James Hardie and LP SmartSide are the two most-specified products in the region. Here’s a side-by-side breakdown.

James Hardie HardiePlank

James Hardie is the market leader in fiber cement siding. HardiePlank lap siding is the most common product, but Hardie also makes vertical panels (HardiePanel), shingles (HardieShingle), and trim.

Composition: Portland cement, sand, and cellulose fiber. 100% non-combustible.

For the Pacific Northwest: Hardie makes HardieZone products specifically engineered for high-moisture climates like western Washington (HZ10). The HZ10 formulation has enhanced moisture-resistant additives.

Warranty: 30-year non-prorated product warranty, 15-year ColorPlus finish warranty.

LP SmartSide

LP SmartSide is an engineered wood siding — it’s made from treated wood fiber, not cement. It’s significantly lighter than Hardie, easier to cut and install, and has a very natural wood-grain appearance.

Composition: Wood fiber treated with zinc borate and resin overlay.

Warranty: 50-year limited product warranty, 5-year finish warranty (much shorter than Hardie’s 15-year finish warranty — relevant in a climate with significant UV and rain).

Cost Comparison — Installed, King County

ProductCost Installed (1,500 SF home)
LP SmartSide Lap$14,000–$20,000
Hardie Plank (primed + painted)$16,000–$24,000
Hardie ColorPlus (pre-finished)$19,000–$28,000

Pricing includes removal of existing siding, installation, trim work, caulking, and final paint coat where applicable.

Which Is Better for Western Washington?

In the Puget Sound climate, the key concerns are:

Moisture: Both products handle moisture well if properly installed. Hardie’s cement core is inherently moisture-resistant. LP SmartSide’s wood fiber is treated but can absorb moisture if the finish is breached — this matters more in western Washington’s wet climate.

Fire resistance: Hardie is non-combustible. LP SmartSide is not. For homes in the wildland-urban interface east of the Cascades, this matters significantly. For most Puget Sound properties, it’s less of a factor.

Installation: LP SmartSide installs faster (lighter, easier cuts) — some contractors prefer it. Hardie is heavier and requires specialized cutting tools. A licensed, experienced contractor makes either product perform correctly.

As a James Hardie preferred contractor, Prolific’s installations are backed by the Hardie installation warranty — the only fiber cement warranty that covers both product and labor.

Get a siding 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

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