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.

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About NW ADU Builders

Local builders. Honest pricing. 93+ ADUs across the Puget Sound since 2007.

— Our Story

Built by locals, for locals.

NW ADU Builders was founded in 2007 by a team of Pacific Northwest builders who saw a problem: homeowners wanted to build ADUs, but the process was fragmented, confusing, and full of hidden costs.

We created a one-stop solution — design, permits, and construction under one roof — with transparent, fixed-price contracts. No subcontractor finger-pointing. No surprise change orders. Just honest building.

Since then, we've completed 93+ ADU projects across King, Pierce, and Snohomish counties. We know every permit office, every inspector, and every zoning nuance in the region. That local knowledge is our biggest advantage — and it saves our clients time and money on every build.

— Our Values

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Transparency

Fixed-price contracts, detailed scopes, no hidden fees. You know exactly what you're paying for.

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Craftsmanship

We build to last 50 years. Quality materials, skilled trades, thorough inspections at every phase.

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Accountability

One team, one point of contact, no finger-pointing. We own every aspect of your project.

— Milestones

Our journey so far.

2007

Founded in Seattle by local builders focused on residential construction

— The Team

A licensed architect, a 22-year GC, and a former Seattle DCI plans examiner.

Every ADU we build is led by a named expert. Meet the people who design, permit, and construct your project.

Meet the team →

Ready to work with us?

Schedule Your Free Consultation →