
About Our ADU Construction Service in Seattle
Key Features & Benefits
Seattle + Eastside service area
Transparent estimates & timelines
Material and finish guidance
Clean job sites & respectful crews
Code-aware, detail-focused work
Quality craftsmanship & durable finishes
Flexible remodeling scopes (single room to full home)
On-site walkthroughs and progress updates
PNW-ready materials (moisture, wear, and maintenance friendly)
Our ADU Construction Process
Free Consultation & Walkthrough
Plan, Design & Materials
Detailed Quote & Schedule
Build & Project Updates
Final Walkthrough & Punch List
Free Consultation & Walkthrough
We visit your home, learn your goals, take measurements, and confirm scope, constraints, and priorities.
Plan, Design & Materials
We help you finalize layout, finishes, and materials that match your style, budget, and Seattle-area home needs.
Detailed Quote & Schedule
You get a clear estimate and timeline. We align expectations before work starts, not after things go sideways.
Build & Project Updates
Our team completes demolition, construction, and installation with consistent communication and job-site cleanliness.
Final Walkthrough & Punch List
We verify details, address touch-ups, and hand off a finished space you’ll actually enjoy living in.
Recent ADU Construction Projects in Seattle

Plan Your ADU Construction Project
How Much Does it Cost to Build an ADU in Seattle? (2026 Guide)
What a Seattle ADU really costs in 2026 — $77.7K–$219.1K attached vs. $199K–$303K+ detached. Full line-item breakdown, soft costs, build timeline, and rental ROI.
Read the guideEstimate your adu construction cost
Configure scope and get an itemized material + labor breakdown for your specific Seattle project.
Open the calculatorADU Construction in Seattle: Common Questions
How much does an ADU cost to build in Seattle?
Kolmo's estimator prices a 600–1,000 sq ft detached ADU (DADU) in Seattle at about $199,000–$303,000 with standard finishes. Attached ADUs run about $77,700 for a 400 sq ft basement conversion to $219,100 for a 1,000 sq ft attached addition, and a garage-conversion ADU about $76,500–$99,800. Each is ±15%, priced 2026-10-28, and includes design, permits, foundation, framing, systems and finishes.
How long does ADU construction take in Seattle?
The full ADU process in Seattle takes 12–18 months: 1–3 months for design, 3–6 months for Seattle DCI permit approval, and 4–8 months for construction. Prefab ADUs can shorten construction to 2–3 months after permit approval.
What ADU types are allowed in Seattle?
Seattle allows detached ADUs (DADUs) up to 1,000 sq ft, attached ADUs, and garage conversions on most single-family lots. Seattle removed owner-occupancy requirements in 2019, allowing you to rent both the main home and the ADU simultaneously.
Ready to Start Your ADU Construction Project in Seattle?
Contact us today to schedule a free consultation and get a detailed quote. Our licensed team is ready to bring your vision to life with expert craftsmanship and attention to detail.
Or call us directly at (206) 410-5100

