ADU CraftSeattle
Small dark backyard cabin with a deck among trees at dusk
Craftsman house with a covered porch framed by trees
New open living room with a gray sectional and big windows onto trees
ADU builder · Seattle, WA

Backyard cottages and in-home units for Seattle lots.

Detached ADUs, attached and basement units and garage conversions. We check your lot against Seattle and Washington rules, design it and build it.

Check what my lot allows Seattle ADU costs
  • Up to two ADUs
  • No parking required
  • Licensed & insured

How many ADUs can I build in Seattle?

Up to two on most residential lots, as of November 2026: two attached, two detached, or one of each. Seattle's 2025 changes raised the height limit for ADUs in Neighborhood Residential zones to 32 feet and kept a 1,000-square-foot cap on above-ground floor area, with more allowed when converting existing space. Off-street parking is not required, and the owner does not have to live on site.

See the full cost guide

What kinds of ADUs do we build in Seattle?

Five ways to add a unit, from a backyard cottage to a basement conversion.

Small blue backyard cottage with a covered porch

Backyard cottage (DADU)

A free-standing backyard home with its own kitchen, bath and entry.

Backyard cottage (DADU)
Garage converted with French doors and a window, car parked in front

Garage conversion

Reuse the slab, walls and roof you already have.

Garage conversion
Small bungalow with a covered porch and a lawn

Attached ADU

A side or rear addition that is a full, separate unit.

Attached ADU
Living room with a fireplace, plants and an orange pendant lamp

In-home ADU

Turn a basement or part of the house into a separate home.

In-home ADU
Floor plan drawing with symmetrical rooms on pale green paper

Design and permits

Custom or pre-approved plans, submitted and tracked.

Design and permits

Why Seattle builds so many backyard cottages

Seattle removed owner-occupancy and off-street parking requirements for ADUs in 2019, and its 2025 updates raised ADU heights in Neighborhood Residential zones. Washington's HB 1337 also requires cities to allow two ADUs per lot.

The city's 2025 middle-housing rules count ADUs toward the number of homes allowed on a lot. Your plan should fit that total as well as the ADU rules.

Purple house behind a wood trellis, garden steps and fall foliage

How does an ADU project work?

  1. Lot checkZoning, setbacks, easements and utility routes for your address.
  2. DesignFloor plans sized to the yard and the budget.
  3. PermitsPlans submitted and followed through city review.
  4. BuildConstruction, inspections and final sign-off.

Inside the units we build

Kitchens, living spaces and baths for small Seattle homes.

Open kitchen with stools and a living area under a sloped ceiling
Open kitchen with stools and a living area under a sloped ceiling
Small dining area with a round table beside the kitchen
Small dining area with a round table beside the kitchen
Bathroom with a navy vanity, brass faucet and a tub-shower
Bathroom with a navy vanity, brass faucet and a tub-shower
Backyard gazebo among flowering shrubs with a house beyond
Backyard gazebo among flowering shrubs with a house beyond

Seattle neighborhoods we serve

All of Seattle. Four pages cover what we see most.

Row of waterfront houses below a wooded hillside in autumn

Ballard

Craftsman lots and alley access.

ADUs in Ballard
Shingled rooftop below tall evergreen trees

West Seattle

Hillside lots and view considerations.

ADUs in West Seattle
Blue-gray two-story house with a balcony and a brick chimney

Beacon Hill

Older homes and near light rail.

ADUs in Beacon Hill
Street of older houses with a garage under bare spring trees

Wallingford

Compact lots and basement units.

ADUs in Wallingford

Is your lot ready for an ADU?

Send your address and a sentence about what you want. We look up the zoning, setbacks and utility routes and reply with the ADU types that fit.

We build in Seattle, WA.

We use your details only to answer this request. Your address is never published.

Seattle ADU questions

What are the ADU rules in Seattle? Can I build two ADUs in Seattle? Do ADUs need parking in Seattle? How much does an ADU cost in Seattle? How long does it take to build an ADU in Seattle?