ADU Rules in Richland, Washington

Richland (population ~60,000) is a Benton County city in the Tri-Cities region of southeastern Washington, with a unique identity shaped by its origins as a US government-built town to house workers at the Hanford Nuclear Site during World War II's Manhattan Project. Today Richland is home to Pacific Northwest National Laboratory (PNNL), a major US Department of Energy national laboratory conducting nuclear and environmental science research. The city sits along the Columbia River near the Hanford Reach National Monument. Richland 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 Richland. 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
• State law limits how restrictive local setback, lot coverage, and height standards for ADUs can be

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

Richland is subject to the Washington Growth Management Act (GMA) and has a comprehensive plan with an Urban Growth Area coordinated with Benton County and the Tri-Cities regional planning framework.

Richland Local ADU Code

Richland's Community Development Department administers local zoning and building permits. Local ADU regulations must comply with HB 1337 and cannot be more restrictive than state law allows.

Permitted ADU Types

• Detached ADU: A standalone 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 Richland from requiring ADUs smaller than 1,000 square feet. Confirm current maximum size limits for your zone with Richland's Community Development Department.

Setbacks

HB 1337 limits Richland's ability to impose setbacks that would prevent reasonable ADU construction. Setback requirements vary by zoning district. Verify current standards with the city before designing.

No Owner-Occupancy Requirement

State law prohibits owner-occupancy mandates. Richland cannot require property owners to live on-site to rent an ADU.

Hanford Nuclear Site — Environmental Legacy

The Hanford Site is the most contaminated nuclear site in the United States, containing an estimated 56 million gallons of high-level nuclear waste in underground storage tanks and extensive soil and groundwater contamination. The US Department of Energy (DOE) manages an ongoing, multi-billion-dollar cleanup effort. Key considerations for Richland property owners:

• Columbia River: Hanford groundwater contaminated with various radionuclides (including tritium, iodine-129, and others) flows toward the Columbia River. Washington DOE and EPA monitor the Columbia River and provide public updates
• PNNL: Pacific Northwest National Laboratory operations within Richland are managed under strict DOE environmental and safety protocols
• Residential properties: Richland's residential neighborhoods are physically separated from the Hanford Site, which has its own security perimeter. However, proximity to Hanford is a factor some buyers research carefully

Consult Washington DOE's Hanford Cleanup program (ecology.wa.gov/Hanford) and the DOE Hanford Site website for the most current environmental data.

Critical Areas Ordinance (CAO)

Richland's CAO protects the Columbia River shoreline (including the Hanford Reach, a free-flowing stretch of the Columbia and protected salmon habitat), riparian corridors, wetlands, and other critical areas. The Hanford Reach National Monument directly borders Richland to the north. CAO buffers along the Columbia River and other water features can restrict ADU siting near the waterfront. Check Richland's GIS mapping for CAO constraints.

Wildfire Risk

Eastern Washington's dry climate creates significant wildfire risk. Sagebrush steppe and dry grasslands surrounding Richland are fire-prone. Properties at the urban-rural interface may be in WUI zones subject to additional fire-resistant construction standards.

Seismic Hazard

Richland and eastern Washington face seismic risk from the Cascadia Subduction Zone (CSZ) and local fault systems. All construction must meet Washington State Building Code seismic requirements.

Permit Process

1. Check your property's zoning and CAO constraints at Richland's online GIS portal
2. Contact Richland's Community Development Department for pre-application guidance
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application at ci.richland.wa.us or in person at 625 Swift Blvd
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Richland Community Development: (509) 942-7560 | ci.richland.wa.us

Disclaimer: This guide provides general information based on Washington HB 1337 (2023) and Richland's municipal code as of April 2026. Hanford-related environmental information is for general awareness — consult Washington DOE and US DOE for current site-specific data. Always verify current zoning requirements with City of Richland Community Development before making development decisions. This is not legal advice.