ADU Rules in Spokane Valley, Washington

Spokane Valley (population ~105,000) is a suburban city in Spokane County, incorporated in 2003 as one of Washington's newest and fastest-growing cities. Located along the Spokane River immediately east of the City of Spokane, Spokane Valley is now one of the 10 largest cities in Washington State. Despite sharing a name and geography with its neighbor, Spokane Valley has its own independent municipal government, zoning code, and permit system. The city is subject to Washington's statewide ADU reform laws.

Washington State ADU Law: HB 1337 (2023)

Washington HB 1337 (2023) is the foundational statewide ADU law that applies to Spokane Valley. Core requirements:

• Cities must allow up to 2 ADUs per lot — one attached/internal + one detached — by right on any lot with a single-family home
• No owner-occupancy requirement permitted
• No ADU-specific impact fees allowed
• Cities may not require ADUs smaller than 1,000 square feet
• Setback, lot coverage, and height standards for ADUs are limited by state law

Washington HB 1110 (2023) accompanies HB 1337, requiring Spokane Valley to allow duplexes and middle housing in residential zones.

Spokane Valley is subject to the Washington Growth Management Act (GMA) and has a comprehensive plan with an Urban Growth Area coordinated with Spokane County.

Spokane Valley Local ADU Code

Spokane Valley's Community & Public Works Department administers local zoning and building permits. As a relatively young city, Spokane Valley's code was developed after incorporation in 2003 and has been updated to incorporate state mandates including HB 1337.

Permitted ADU Types

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

Up to 2 ADUs per lot are permitted (one attached/internal + one detached).

Size Limits

State law prohibits Spokane Valley from requiring ADUs smaller than 1,000 square feet. Confirm current maximum size limits for your zoning district with Spokane Valley's Planning Division.

Setbacks

HB 1337 limits Spokane Valley's ability to impose setbacks that would prevent reasonable ADU construction. Setback requirements vary by zone. Verify current standards with the Permit Center.

No Owner-Occupancy Requirement

State law prohibits owner-occupancy mandates. Spokane Valley may not require property owners to live on-site to rent an ADU.

Critical Areas Ordinance (CAO)

Spokane Valley's CAO protects the Spokane River corridor (a significant fish and wildlife habitat), wetlands, frequently flooded areas, steep slopes and geologically hazardous areas, and critical aquifer recharge areas. The Spokane-Rathdrum Prairie Aquifer, a sole-source aquifer providing drinking water to the Spokane region, is particularly protected under the CAO. Properties near the Spokane River, wetlands, or on steep valley slopes may have CAO-imposed buffers restricting ADU siting. Review Spokane Valley's GIS mapping tools to identify CAO-regulated features on your property.

Seismic and Wildfire Risk

Spokane Valley has lower seismic risk than western Washington but is not immune to earthquake hazard from the Cascadia Subduction Zone or local faults. All construction must meet Washington State Building Code seismic requirements.

Eastern Washington's drier climate creates significant wildfire risk. Parts of the Spokane Valley urban-rural interface are in or near Wildland-Urban Interface (WUI) zones. Properties at the WUI boundary may be subject to additional fire-resistant construction requirements. Check Spokane County's WUI maps for your property's classification.

Permit Process

1. Verify your property's zoning and any CAO constraints using Spokane Valley's GIS tools
2. Contact Spokane Valley's Planning Division for pre-application guidance
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application online at spokanevalley.org/permits or in person at 10210 E Sprague Avenue
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Spokane Valley Permit Center: (509) 720-5240 | spokanevalley.org

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