— Backyard Cottage

    Detached ADU (DADU) Builders — Seattle, Tacoma & Puget Sound

    A fully independent structure built in your backyard. This is the most popular ADU type in the Puget Sound region — offering maximum privacy, the best rental income potential, and the highest property value increase. We've built over 25 DADUs across King and Pierce County.

    400–900 sq ft
    $185k–$320k
    6–8 month construction phase
    Custom or pre-approved plans

    Why a backyard cottage is the strongest ADU investment

    A detached ADU is a second legal home on your lot: its own entrance, kitchen, bath, and address, with nothing shared but the parcel. That independence is why DADUs out-earn attached units as rentals, why they carry the highest appraised-value increase of the three ADU types, and why they are the most popular ADU we build across King and Pierce County. Under Washington's HB 1337, every single-family lot has the right to two ADUs — a DADU can stand alone or pair with a basement suite.

    Custom design or pre-approved plans

    There are two routes to a permitted DADU. A custom design gives you a cottage shaped around your lot, trees, and light — our architects handle it end to end. Pre-approved plan sets (like Seattle's ADUniverse program) trade some flexibility for a meaningfully faster permit review. We build both; feasibility tells you which fits your parcel and timeline.

    Not sure whether your parcel supports a backyard cottage at all? Read will your lot qualify for a DADU for the five site factors — size, setbacks, slope, sewer, and access — we check before quoting.

    One fixed price, permit to keys

    The quote covers the whole project: architectural drawings, engineering stamps, site survey and soil testing, every permit application and city fee, foundation through roofing, full MEP, interior finishes, landscaping restoration, and the final inspection with certificate of occupancy. The number on page one is the number at closeout.

    What's Included

    • Full architectural design & drawings
    • Engineering stamps & structural calcs
    • Site survey & soil testing
    • All permit applications & city fees
    • Foundation, framing, roofing
    • MEP (plumbing, electrical, HVAC)
    • Interior finishes & fixtures
    • Landscaping restoration
    • Final inspection & Certificate of Occupancy

    From our portfolio

    West Seattle Sound-View DADU

    A finished detached ADU from our portfolio — see the layout, materials, and yard integration.

    View the project →

    Detached ADU (DADU) FAQs

    How much does a detached ADU cost in the Puget Sound?

    Our detached ADUs run $185,000–$320,000 turnkey for 400–900 sq ft, depending on size, finish level, and site conditions. That covers design, engineering, permits, full construction, utility connections, and certificate of occupancy on one fixed-price contract.

    How long does a DADU take to build?

    The construction phase is 6–8 months for most DADUs. The full journey — design, permitting, then construction — typically lands at 10–16 months depending on the city and whether you use a pre-approved plan.

    Can I put a DADU on my lot?

    Under Washington's HB 1337, every single-family lot has the right to two ADUs, and DADUs are allowed up to 1,000 sq ft in most Puget Sound cities. What actually decides it is your specific parcel — setbacks, slope, sewer location, and access — which is exactly what our free feasibility review checks.

    What does a DADU rent for?

    Typical ADU rents across the Puget Sound market run $1,600–$2,800/mo depending on city, size, and finish. City-by-city context is on our service-area pages.

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