Locations
Spokane ADU rules by jurisdiction
ADU rules differ by jurisdiction. The first step is identifying which one your lot falls under, then reading the current rules for that jurisdiction.
Jurisdiction
City of Spokane
ADU rules for homeowners inside Spokane city limits.
See the rules →Jurisdiction
Unincorporated Spokane County
County ADU rules for parcels outside any city, with the BP-75 and BP-76 sheets.
See the rules →Jurisdiction
Spokane Valley
ADU rules and the permit center for the City of Spokane Valley.
See the rules →Not sure which jurisdiction your property is in? Your county property record lists the jurisdiction, and the cities of Spokane and Spokane Valley each maintain their own permit offices. If your parcel is outside any city, the unincorporated Spokane County rules apply. Once you know your jurisdiction, check whether your lot can support an ADU.
What it costs, and what happens after you send it
- What does an ADU cost in the Spokane area?
- 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