Short answer
Converting a garage into an ADU in Bellevue, Kirkland, Redmond or Seattle costs about $90,000 to $160,000 in 2026 and takes 8 to 14 months from design to move-in. It is usually cheaper than building a new detached ADU because the foundation, walls and roof already exist.
How much does a garage ADU conversion cost?
| ADU type | Typical 2026 cost | Design to move-in |
|---|---|---|
| Interior or basement ADU | $60,000 to $120,000 | 6 to 10 months |
| Garage conversion ADU | $90,000 to $160,000 | 8 to 14 months |
| Detached ADU (new build) | $180,000 to $320,000+ | 12 to 18 months |
The biggest swing factors are whether the slab needs to be raised or insulated, how far water and sewer lines must run, and whether you add a full kitchen and bathroom.
Are garage ADUs allowed in Washington?
Yes. Washington’s House Bill 1337, passed in 2023, requires cities inside urban growth areas to allow up to two ADUs on most residential lots and makes it easier to convert existing structures such as garages. Each city adopts its own code, and local rules still control size, height, parking and utilities, so checking your city early is the first step.
What a garage conversion includes
- Feasibility check. Lot, setbacks, utilities, slab condition and city ADU rules.
- Design and permit drawings. Floor plan, insulation, windows, kitchen and bath layout.
- Slab and envelope. Moisture barrier, insulated floor, framed and insulated walls, and replacing the garage door with a wall, windows or a door.
- Utilities. Water, sewer, electrical panel capacity and heating, often a ductless heat pump.
- Finishes. Kitchen or kitchenette, bathroom, flooring and lighting.
- Inspections and final approval.
What are the biggest surprises?
- Floor height. Garage slabs sit lower than the house and slope toward the door. Leveling and insulating the floor is often required.
- Sewer connection. If the sewer line is far or uphill, a pump may be needed.
- Electrical service. Many older homes need a panel or service upgrade to add a kitchen and heat.
- Parking. Some cities have parking rules for ADUs, so we check them during feasibility.
We build garage ADUs in Kirkland, Redmond, Bellevue, Bothell and across the Eastside. Thinking about family rather than rental? See our mother-in-law suite guide.
Planning a project? Get a free consultation with Renovision Design & Build. Call (425) 276-6501 or send us your project details. Learn more about ADU construction on the Eastside.
Frequently asked questions
How much does it cost to convert a garage into an ADU in Seattle?
About $90,000 to $160,000 in 2026 for a full ADU with a kitchen and bathroom in the Seattle and Eastside area.
Is a garage conversion cheaper than a detached ADU?
Yes. A garage ADU costs about $90,000 to $160,000, compared with $180,000 to $320,000+ for a new detached ADU.
How long does a garage ADU conversion take?
Plan on 8 to 14 months from the first design meeting to move-in, including permit review.
Can I rent out a garage ADU in Washington?
Generally yes, ADUs can be rented, but check your city’s current code and any HOA covenants before you plan on rental income.
Can I turn half a garage into living space?
Yes. Converting part of a garage into an office or studio is a smaller project and may not need to meet full ADU rules.
