ADUs & DADUs in Seattle
Since Seattle’s 2019 ADU reforms, most single-family lots can add a backyard cottage (DADU) or an attached unit (AADU). It’s the highest-value square footage you can build here — rental income, family space, or future flexibility.
We know Seattle’s ADU rules cold
Seattle now allows up to two ADUs on most single-family lots, removed owner-occupancy requirements, and eased parking and size limits. But the size caps, height limits, lot-coverage and tree rules still trip people up. We run a feasibility study first so you know exactly what your lot allows before you spend on design.
Detached (DADU) or attached (AADU)
A DADU is a standalone backyard cottage — the most popular choice for rental income and privacy. An AADU converts part of your home (often a basement) into a legal unit with its own entrance, egress and kitchen. We build both, and help you choose based on your lot, budget and goals.
Permits, utilities & the build
ADUs touch sewer, water, power and sometimes side-sewer capacity — plus the full SDCI permit set. We coordinate the whole thing: survey, design, structural and energy code, permitting, utility connections and construction, finished to rent or move in.
Typical Seattle pricing
| Option | Typical Seattle range |
|---|---|
| Basement AADU conversion | $150,000 – $300,000 |
| Detached DADU (1-bed) | $250,000 – $350,000 |
| Detached DADU (2-bed / larger) | $350,000 – $450,000+ |
| Feasibility study | flat fee, credited to your build |
Prices in USD. Every project gets a written, fixed-scope estimate after a free in-home consultation.
ADUs & DADUs — your questions
Can I build a DADU on my Seattle lot?
Most single-family lots qualify under Seattle’s 2019 ADU reforms, subject to size, height, lot-coverage and tree rules. We run a feasibility study to confirm exactly what your specific lot allows.
How much does a DADU cost in Seattle?
A typical detached backyard cottage runs $250k–$450k all-in (design, permits and construction), depending on size, finishes and site/utility conditions.
Will a DADU pay for itself?
Many Seattle owners rent a DADU for $1,800–$2,800/month, and it adds significant property value. We can model the numbers for your lot during feasibility.
Explore more
Get your free Seattle estimate
A licensed design-build team, honest numbers up front, and no surprise change-orders.