What a real Seattle ADU builder does
Hiring an ADU builder in Seattle is not the same as hiring a remodeler. An accessory dwelling unit is a second legal home on your lot — it triggers zoning review under SMC 23.44.041, structural engineering, separate utility connections, and its own certificate of occupancy. A real Seattle ADU builder owns all of that, on a single contract, with one price.
What that looks like in practice: feasibility study on your specific parcel, schematic design, SDCI permit submittal with every correction cycle handled in-house, foundation through final inspection, side-sewer and electrical service coordination with SPU and Seattle City Light, and a walkthrough with a tenant-ready unit at the end.
Our Seattle service area
We build across Seattle proper — Ballard, Greenwood, Phinney Ridge, Wallingford, Green Lake, Ravenna, Wedgwood, Maple Leaf, Beacon Hill, Columbia City, West Seattle, Queen Anne, Magnolia, and the rest of the city's single-family zones (now Neighborhood Residential). We also serve Bellevue, Kirkland, Redmond, and the broader Puget Sound — see all service areas.
2026 Seattle ADU pricing
- 400–500 sq ft studio DADU: $185,000–$220,000
- 600–800 sq ft 1-bed DADU: $200,000–$280,000 (most common)
- 900–1,000 sq ft 2-bed DADU: $270,000–$350,000
- Garage conversion AADU: $140,000–$190,000
- Basement AADU: $120,000–$200,000
All-in: design, engineering, SDCI permits, full construction, utility connections, certificate of occupancy.
Our 5-step process
- Feasibility (free, 1 week): zoning, setbacks, sewer location, utility capacity.
- Design & fixed-price contract (3–6 weeks): floor plan, elevations, finish selections, locked price.
- SDCI permitting (2–14 weeks): pre-approved plans clear fastest; custom designs go through standard intake.
- Construction (6–8 months): weekly written progress reports.
- Closeout: final inspections, certificate of occupancy, 2-year workmanship warranty, tenant-ready handover.
How to vet any Seattle ADU builder
- Active Washington L&I contractor license (verify at lni.wa.gov).
- Fixed-price contract — not cost-plus, not "T&M with a not-to-exceed."
- At least 10 finished Seattle ADUs you can drive past.
- SDCI experience — ask which reviewers they last worked with.
- References from owners who closed within the last 24 months.
Related reading: City of Seattle DADU requirements (2026).
Seattle ADU FAQs
How much do Seattle ADU builders charge in 2026?
Turnkey pricing from licensed Seattle ADU builders in 2026 runs $185,000–$220,000 for a 400–500 sq ft studio, $200,000–$280,000 for a 600–800 sq ft 1-bedroom DADU, and $270,000–$350,000 for a 900–1,000 sq ft 2-bedroom. Pricing covers design, engineering, permits, full construction, utility connections, and certificate of occupancy.
How long does it take to build an ADU in Seattle?
From signed contract to certificate of occupancy: 9–14 months total. Design and permitting take 3–5 months (2–6 weeks with a SDCI pre-approved plan; 8–14 weeks for custom). Construction is 6–8 months for most DADUs.
Do Seattle ADU builders handle permits?
Yes. A real Seattle ADU builder runs the entire SDCI permit package — zoning review, MUP if needed, building, mechanical, electrical, plumbing, and side-sewer permits — and tracks every correction cycle in writing. Avoid any builder who asks you to pull permits yourself.
What's the difference between an ADU, AADU, and DADU?
ADU is the umbrella term (Accessory Dwelling Unit). AADU is an Attached ADU built inside or attached to the main house (basement conversion, second-story addition). DADU is a Detached ADU — a freestanding backyard cottage on the same lot.
How do I choose a Seattle ADU builder?
Five checks: (1) Washington L&I contractor license and bond, active and clean. (2) Fixed-price contract — not cost-plus. (3) At least 10 completed Seattle ADUs you can drive past. (4) In-house design or a dedicated architect partner familiar with SDCI. (5) References from owners who finished in the last 24 months.
Can I finance an ADU build in Seattle?
Yes. The three common routes are a HELOC against your existing home equity, a renovation/construction loan (Fannie Mae HomeStyle, FHA 203k), or a cash-out refinance. Washington State also has an ADU loan program through some local credit unions specifically for ADUs returning rental income.
How many ADUs can I build on my lot in Seattle, WA in 2026?
In Seattle, Washington's HB 1337 gives every single-family lot the right to two ADUs — attached, detached, or a combination. Under HB 1337, every SF lot in Seattle can host two ADUs (attached, detached, or two DADUs), with no owner-occupancy requirement and no off-street parking mandated. DADUs can reach 1,000 sq ft or 60% of the main home. Seattle's ADUniverse pre-approved plans can compress permit review to about 6 weeks.
Do I have to live on the property to rent out my Seattle ADU?
No. HB 1337 removed statewide owner-occupancy requirements, including in Seattle. You can rent both the main home and the ADU on long-term leases. Short-term rentals remain separately regulated.