ADU Rules in Spokane, Washington

Spokane is eastern Washington's largest city (population ~230,000), the county seat of Spokane County, and the regional economic and cultural hub for the Inland Pacific Northwest. Located along the Spokane River, Spokane is home to Gonzaga University and serves as a gateway between Washington and Idaho. The city is subject to Washington's statewide ADU reform laws, making it significantly easier to add dwelling units to residential lots.

Washington State ADU Law: HB 1337 (2023)

Washington HB 1337 (2023) is the primary statewide ADU law governing Spokane and all Washington cities. Its key requirements:

• Cities must allow up to 2 ADUs per lot on any lot with a single-family home — one attached/internal + one detached — by right
• No owner-occupancy requirement permitted
• No ADU-specific impact fees allowed
• Cities may not require ADUs to be smaller than 1,000 square feet
• Restrictions on setback, lot coverage, and height standards that would effectively prevent ADU construction

Washington HB 1110 (2023) accompanies HB 1337 by requiring cities to allow duplexes and other middle housing types in residential zones, expanding Spokane's housing density options.

Spokane is subject to the Washington Growth Management Act (GMA), which requires the city to have a comprehensive plan with an Urban Growth Area (UGA) and to zone consistently with planned growth targets.

Spokane Local ADU Code

Spokane's zoning code is administered by the Spokane City Planning and Development Services Department. Local ADU rules must comply with HB 1337 and cannot be more restrictive than state law allows.

Permitted ADU Types

• Detached ADU: A separate structure in the rear or side yard
• Attached ADU: An addition sharing at least one wall with the primary home
• Internal/Converted ADU: Conversion of existing basement, attic, or garage space

Up to 2 ADUs per lot are permitted — one attached/internal and one detached.

Size Limits

State law prohibits Spokane from requiring ADUs smaller than 1,000 square feet. Consult Spokane Planning and Development Services for the current maximum size standards in your zone.

Setbacks

State law limits Spokane's ability to impose setbacks that would prevent reasonable ADU placement. Typical residential setbacks in Spokane include front, side, and rear yard requirements that vary by zoning district. Confirm current setback standards with the city's planning department.

No Owner-Occupancy Requirement

HB 1337 prohibits owner-occupancy mandates. Spokane cannot require property owners to live on-site to rent out an ADU.

Critical Areas Ordinance (CAO)

As a GMA jurisdiction, Spokane maintains a Critical Areas Ordinance protecting wetlands, fish and wildlife habitat (Spokane River corridor), frequently flooded areas, geologically hazardous areas including steep slopes, and critical aquifer recharge areas. The Spokane-Rathdrum Prairie Aquifer, a sole-source aquifer that supplies drinking water to the region, is particularly sensitive. CAO buffers can restrict where on a lot an ADU may be sited. Review Spokane's CAO maps before finalizing ADU placement.

Seismic Hazard

Spokane is in eastern Washington, which has lower seismic risk than the Puget Sound region but is not immune to earthquake hazard. The Cascadia Subduction Zone offshore can produce shaking throughout Washington. Local fault systems in eastern Washington are also a consideration. ADU construction should meet Washington State Building Code seismic provisions. Geotechnical review may be advisable for sites with poor soils.

Wildfire Risk — WUI Considerations

Parts of Spokane and the surrounding Spokane County urban-rural interface lie in the Wildland-Urban Interface (WUI). Eastern Washington receives significantly less rainfall than western Washington, and the region experiences periodic large wildfires. Properties in WUI areas may be subject to additional construction requirements under the Washington State Building Code, including ignition-resistant construction materials and defensible space standards. Check Spokane County's WUI maps to determine your property's fire hazard classification.

Permit Process

1. Check your property's zoning and any CAO constraints using Spokane's online GIS portal
2. Consult Spokane Planning and Development Services for pre-application guidance
3. Prepare construction drawings meeting Washington State Building Code requirements
4. Submit a building permit application to Spokane's Permit Center
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Spokane Planning & Development Services: (509) 625-6300 | spokanecity.org/permittingcenter

Disclaimer: This guide provides general information based on Washington HB 1337 (2023) and Spokane's municipal code as of April 2026. Zoning regulations change frequently. Always verify current requirements with the City of Spokane before making development decisions. This is not legal advice.