What is the difference between an ADU and a DADU?

An ADU (accessory dwelling unit) is a secondary living space attached to or inside your main home, like a basement or garage conversion. A DADU (detached accessory dwelling unit), often called a backyard cottage, is a separate standalone structure on the same lot. Both have a full kitchen, bathroom, and sleeping area, and both can typically be rented out or used for family.

How much does it cost to build a DADU in the Seattle–Tacoma area?

Cost depends on size, site conditions, and finish level, but detached units in the Puget Sound region commonly range from about $250,000 to $450,000 or more. We provide a fixed-price contract after a site evaluation, so your number does not move once the scope is set.

How long does an ADU or DADU project take?

Plan on roughly 10 to 16 months end to end for a detached unit: design and engineering (1 to 3 months), permitting (varies by jurisdiction, often 3 to 6 months), and construction (4 to 7 months). Timelines vary by city and site, and we manage all three phases.

Do I need a permit, and can you handle it?

Yes. ADUs and DADUs require permits, and the rules differ between Seattle, King County, Pierce County, and individual cities. We handle design, engineering, and the full permitting process as part of the contract, so you do not deal with the jurisdiction directly.

Can I rent out my ADU?

In most Puget Sound jurisdictions, yes. ADUs can be rented long term, and many homeowners use them for rental income, multigenerational living, or a home office. Specific rules such as short-term rental limits vary by city, and we confirm what applies to your lot.

What areas do you serve?

We build throughout King County and Pierce County, including Seattle, Tacoma, Bellevue, Renton, Kent, Federal Way, and Puyallup.

How much does an ADU cost in Seattle?

ADU costs in the Seattle area range from $85,000 for a basic garage conversion to $350,000+ for a custom detached cottage. The most popular build — a 600–800 sq ft DADU — typically runs $200,000–$280,000 including design, permits, and construction.

How long does the permit process take?

Using pre-approved plan sets, we can secure permits in 2–6 weeks in most King County jurisdictions. Custom designs take 8–12 weeks. Seattle DCI has expedited ADU review pathways that we leverage on every project.

Can I use my ADU as a rental?

Yes. Washington state allows ADU rentals in most residential zones. In Seattle, you can rent both a DADU and an attached ADU (two ADUs per lot). Average rental income for a well-finished ADU in Seattle is $2,200–$3,000/month.

Do I need to move out during construction?

No. For detached ADUs, construction happens entirely in your backyard. For garage conversions or basement ADUs, there may be 1–2 weeks of interior disruption during utility connections.

What areas do you serve?

We serve all of King County, Pierce County, and Snohomish County including Seattle, Bellevue, Kirkland, Redmond, Tacoma, Puyallup, Federal Way, Everett, and Lynnwood.

Home / How It Works

How It Works

Our proven 5-step process — refined across 93+ builds.

— 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.

Free Site Visit

We visit your property, assess zoning, soil, setbacks, utility connections. Same-day feasibility verdict.

1–2 days

Design & Quote

Architectural floor plans, 3D renders, engineering, detailed fixed-price proposal.

1–2 weeks

City Permits

We submit and track permits with Seattle DCI / Pierce County. We handle all revisions and inspector communications.

4–8 weeks

Construction

Site prep, foundation, framing, MEP, insulation, finishes. Weekly photo updates via text.

3–6 months

Move-In Ready

Final inspection, punch list, CO (Certificate of Occupancy). You get keys. We help you set rental price.

1 week

How It Works

From backyard to rental income in 5 steps.

Free Site Visit

Design & Quote

City Permits

Construction

Move-In Ready

Frequently Asked Questions

How much does an ADU cost in Seattle?

How long does the permit process take?

Can I use my ADU as a rental?

Do I need to move out during construction?

What areas do you serve?