ADU type
Garage Conversion ADU
Converting an existing garage into a livable ADU reuses a structure that is already built, which can make it one of the lower-cost ways to add a unit. The right fit depends on the garage, the lot, and your jurisdiction.
Why a garage conversion can cost less
A garage conversion starts with an existing foundation, walls, and roof, so you are adapting a structure rather than building one from the ground up. That can reduce site work and shell costs compared with a new detached unit. The savings vary widely based on the condition of the garage and how much new plumbing, insulation, and electrical the unit needs. Compare it with the other ADU types in our Spokane ADU cost guide.
Typical scope of work
- Insulating walls, floor, and roof to meet residential energy requirements.
- Adding or upgrading plumbing for a kitchen and bathroom.
- Upgrading electrical service and adding heating and cooling.
- Replacing the garage door with a wall, windows, and an entrance.
- Raising or finishing the slab and addressing drainage where needed.
Feasibility considerations
- Whether the existing slab and framing can support residential use, which the builder and an engineer assess.
- Setbacks and whether the garage already sits where an ADU is allowed.
- How losing covered parking interacts with any parking rules in your jurisdiction.
- Ceiling height, since some older garages are below residential minimums.
- Utility access from the main house to the converted unit.
What the builder handles
A licensed local builder evaluates the garage, designs the conversion, manages permitting with your jurisdiction, and performs the construction. You contract with that builder directly.
Keep researching
What it costs, and what happens after you send it
- What does an ADU cost in the Spokane area?
- For a garage conversion, published estimates put the all-in figure at $50,000 to $120,000. Across types: detached new-build $110,000 to $260,000, garage conversion $50,000 to $120,000, prefab or modular installed $80,000 to $180,000. Add roughly $3,000 to $5,000 in permit, plan review and impact fees, which is an estimate from one source rather than a published fee schedule, so confirm it with your permitting jurisdiction.
- How solid are those numbers?
- Treat them as planning ranges, not prices. They come from two third-party estimator sites, ADU Zoning and ADU Wizard, both read in full on 2026-08-17, neither of them a government publication. The two land in nearly the same place on total project cost, which is why totals are shown here. They differ by roughly a factor of two on cost per square foot, so a per-square-foot rate is not a reliable way to budget an ADU here and none is quoted.
- How fast will someone get back to me?
- Your request goes to an independent local ADU builder, usually within about an hour during the day. The builder then contacts you to look at the property and price the project on their own schedule.
- What types are covered?
- Detached ADUs, attached ADUs, garage conversions and basement junior ADUs. See every type.
Only a builder standing on your lot can price your actual project.
Get a free quote from a Spokane ADU builder
Tell us about your lot and project. A builder who serves your jurisdiction prices it, free and with no obligation.
Updated