Exterior
Western Red Cedar Siding
Rain-screen gap · stainless fasteners
Locally milled cedar with a vented rain-screen behind every plank. Water drains, the wall dries — no rot, no warping after the first wet winter.
Seattle · Tacoma · Est. 2007
NW ADU Builders — Premium ADU & DADU Construction in Seattle, Tacoma & the Puget Sound
Premium detached ADUs, garage conversions, and basement cottages crafted for Pacific Northwest homes. We don't just build square footage — we curate places to live.
5.0· Google Reviews
WA Licensed · Bonded · Insured93+
ADUs Built
6mo
Avg. Timeline
3
Counties Served
Quick Answer
What NW ADU Builders does — in one paragraph.
NW ADU Builders designs, permits, and builds ADUs and DADUs (backyard cottages) across Seattle, Tacoma, and the Puget Sound. A detached ADU typically costs $250,000–$450,000 and takes about 10–16 months end to end — with design, permitting, and construction covered in one fixed-price contract.
- 93+ ADUs built across the Puget Sound
- Fixed-price contracts (design + permits + build)
- Serving King & Pierce Counties
- Licensed, bonded & insured in Washington
- Free site evaluation
Free AI Feasibility Report
What can you build on YOUR lot?
Get a free AI-powered feasibility report for your property — zoning, what fits on your lot, cost range, and rental potential.
Bellevue DADU · 780 sq ft · $268k ● Seattle Backyard Cottage · 650 sq ft · $241k ● Tacoma Garage Conversion · $112k ● Kirkland DADU · 900 sq ft · $310k ● Renton ADU · 550 sq ft · $198k ● Redmond DADU · 720 sq ft · $258k ● Bellevue DADU · 780 sq ft · $268k ● Seattle Backyard Cottage · 650 sq ft · $241k ● Tacoma Garage Conversion · $112k ● Kirkland DADU · 900 sq ft · $310k ● Renton ADU · 550 sq ft · $198k ● Redmond DADU · 720 sq ft · $258k ●
Instant Estimate
See your ADU's monthly rent & payback in 10 seconds.
Type your zip code and size. We'll show local rent estimates, build cost, and how fast it pays for itself — based on 93+ Puget Sound builds.
ADU ROI Calculator
What could yours earn?
Market match: Bellevue / Medina
Est. rent
$2,808
per month
Build cost
$281k
turn-key
Payback
10.2 yr
simple
Net cash flow assumes 18% operating costs. Free site visit refines numbers.
— Why Choose Us
One team. Zero headaches. Guaranteed.
Most contractors juggle three different subcontractors for design, permits, and construction. We do it all in-house — which means faster timelines, clearer communication, and no finger-pointing when something goes wrong.
We've built over 40 ADUs across the Puget Sound. We know every inspector at Seattle DCI, every permit shortcut in Pierce County, and every zoning rule in Snohomish. That knowledge saves you months and thousands.
Our fixed-price model means the number we quote is the number you pay. Period.
📐
Design Included
Full architectural drawings, engineering stamps, site plans — included in every quote. No surprise design fees.
⚡
Fast Permits
We use Seattle & Tacoma's pre-approved ADU plan sets. Permits in 2–6 weeks instead of 4–6 months.
💰
Fixed-Price Contracts
Detailed scope. Locked price. No change orders unless YOU request changes. Guaranteed in writing.
🌲
NW Local Experts
We live and build here. We know PNW soil conditions, rainfall considerations, and neighborhood design review processes.
— What We Build
Every ADU type, built to last 50 years.
01Most Popular
Backyard Cottage
A fully independent structure in your backyard. Maximum privacy for tenants, maximum rental income for you. Most popular build type in King & Pierce County — we've built 25+.
- ✓ Custom or pre-approved plans
- ✓ 400–900 sq ft
- ✓ 6–8 month build
- ✓ $185k–$320k
02
Garage Conversion
Transform your existing garage into a fully permitted, livable space. Fastest permit path available. Uses existing structure — significant cost savings vs. new construction.
- ✓ Attach to existing structure
- ✓ 400–650 sq ft
- ✓ 3–5 month build
- ✓ $95k–$160k
03Multi-Gen Favorite
Attached or Basement ADU
Add a self-contained suite to your existing home — basement conversion, above-garage addition, or attached unit. Perfect for multi-generational living.
- ✓ Leverages existing foundation
- ✓ 300–700 sq ft
- ✓ 4–6 month build
- ✓ $85k–$180k
— How It Works
From backyard to rental income in 5 steps.
We've refined this process across 93+ builds. You barely have to lift a finger.
1
Free Site Visit
We visit your property, assess zoning, soil, setbacks, utility connections. Same-day feasibility verdict.
1–2 days2
Design & Quote
Architectural floor plans, 3D renders, engineering, detailed fixed-price proposal.
1–2 weeks3
City Permits
We submit and track permits with Seattle DCI / Pierce County. We handle all revisions and inspector communications.
4–8 weeks4
Construction
Site prep, foundation, framing, MEP, insulation, finishes. Weekly photo updates via text.
3–6 months5
Move-In Ready
Final inspection, punch list, CO (Certificate of Occupancy). You get keys. We help you set rental price.
1 weekFrequently Asked Questions
— Our Work
93+ ADUs built across the Puget Sound.
View Project →
DADUBellevue, WA
Bellevue Backyard Cottage
780 sq ft·$268k·5.5 months
View Project →
DADUIssaquah, WA
Issaquah Forest Retreat
820 sq ft·$289k·6 months
View Project →
DADUSeattle, WA
Ballard Modern Studio
560 sq ft·$215k·4.5 months
View Project →
GarageSeattle, WA
Seattle Capitol Hill
520 sq ft·$118k·4 months
View Project →
DADUSammamish, WA
Sammamish Two-Story DADU
1,050 sq ft·$372k·8 months
View Project →
DADUTacoma, WA
Tacoma Point Defiance
650 sq ft·$231k·6 months
View Project →
DADUKirkland, WA
Kirkland Tech Row
900 sq ft·$312k·7 months
View Project →
DADUSeattle, WA
West Seattle Sound View
680 sq ft·$278k·5.5 months
View Project →
BasementRenton, WA
Renton Highlands
480 sq ft·$142k·4.5 months
View Project →
DADURedmond, WA
Redmond East
720 sq ft·$258k·5 months
— Built for the Rain
150 wet days a year. Engineered for every one.
Most builders use the same wall assemblies they'd use in Phoenix. We don't. Every NW ADU is detailed for Puget Sound rain from the foundation up.
Roof
Standing-Seam Metal Roof
26-gauge steel · 50-year finish
Concealed-fastener standing seam sheds Puget Sound rain at any pitch. Snow slides off, moss can't take hold, and it outlasts comp shingles 3-to-1.
Envelope
Vapor-Permeable WRB
Class-III WRB · taped seams
A weather-resistive barrier that blocks bulk water but lets the wall breathe outward — the only assembly that survives 150 rainy days a year.
Hover any material to see the rain.
— Client Stories
What homeowners say after living in their ADU.
"NW ADU Builders took a complicated Bellevue permit process and made it completely painless. They knew exactly which inspectors to call and what they needed. Our DADU was done in 5.5 months and is now renting for $2,800/mo."
Michael T.
Bellevue · Backyard Cottage
"The fixed-price contract was a game-changer. Other contractors gave us ranges. NW ADU gave us a number and stuck to it. Not a single surprise charge over 6 months. Highly recommend."
Sarah & James K.
Kirkland · 900 sq ft DADU
"We wanted a place for my mother-in-law to live nearby but with privacy. The team designed a perfect 650 sq ft cottage with its own entrance, laundry, and small garden. She loves it. So do we."
Rachel M.
Seattle · DADU
— Investment
Transparent pricing. What you see is what you pay.
These ranges reflect our recent builds. Every project gets a custom quote — we'll give you a number within 48 hours of site visit.
Garage / Basement
Conversion
$85k–$160k
300–650 sq ft · 3–5 months
- ✓Design & drawings
- ✓Permit application
- ✓All city fees
- ✓Licensed construction
- ✓MEP (plumbing/electrical/HVAC)
- ✓Interior finishes
- ✓Final inspection
- –Custom architecture
- –Premium finishes
- –Smart home pre-wire
- –Landscaping
- –Priority scheduling
Most Popular
DADU · New Build
Detached Cottage
$185k–$320k
400–900 sq ft · 5–7 months
- ✓Design & drawings
- ✓Permit application
- ✓All city fees
- ✓Licensed construction
- ✓MEP (plumbing/electrical/HVAC)
- ✓Interior finishes
- ✓Final inspection
- –Custom architecture
- –Premium finishes
- –Smart home pre-wire
- –Landscaping
- –Priority scheduling
Large Custom ADU
Premium Custom
$320k+
800–1,200 sq ft · 7–10 months
- ✓Design & drawings
- ✓Permit application
- ✓All city fees
- ✓Licensed construction
- ✓MEP (plumbing/electrical/HVAC)
- ✓Interior finishes
- ✓Final inspection
- ✓Custom architecture
- ✓Premium finishes
- ✓Smart home pre-wire
- ✓Landscaping
- ✓Priority scheduling
ROI Calculator
$1,700
Monthly Net
9.8 yrs
Payback Period
$100,000
10-Year Gain
— Service Area
We build ADUs across the Greater Puget Sound.
Licensed and actively building in King County, Pierce County, and Snohomish County.
King CountyPrimary
Snohomish County
Not sure if we serve your area? Call us — we may travel for larger projects.
Frequently Asked
ADU & DADU questions, answered.
Comparing your options? Read our prefab vs site-built ADU comparison for real 2026 Puget Sound cost and timeline numbers.
— Get Started
Ready to build?
Let's talk about your property.
Free on-site consultation. We come to you, assess your lot, tell you exactly what you can build and for how much. No pressure. No obligation.
⚡We typically respond within 2 business hours