ADU Rules in Renton, Washington

Renton (population ~110,000) is a diverse, fast-growing city in southern King County at the southern tip of Lake Washington. Renton is known for the Boeing 737 assembly plant — one of the most significant aerospace manufacturing facilities in the world — and the Cedar River, an ecologically critical salmon-bearing stream that flows through the city into Lake Washington. Renton 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 Renton. 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 to be 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 Renton to allow duplexes and middle housing in residential zones, significantly changing the density allowed in Renton's single-family neighborhoods.

Renton is subject to the Washington Growth Management Act (GMA), with a comprehensive plan and Urban Growth Area designation coordinated with King County.

Renton Local ADU Code

Renton's Community & Economic Development Department administers local zoning and building permits. Renton's local ADU regulations must comply with HB 1337 and may not 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 to the primary home sharing at least one wall
• Internal/Converted ADU: Conversion of existing garage, basement, or attic space

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

Size Limits

State law prohibits Renton from requiring ADUs smaller than 1,000 square feet. Confirm current maximum size limits with Renton's Community & Economic Development Department for your specific zone.

Setbacks

HB 1337 limits Renton's ability to impose setbacks that would effectively block ADU construction. Setback requirements vary by zoning district. Verify current standards with Renton's Permit Center.

No Owner-Occupancy Requirement

State law prohibits owner-occupancy mandates. Renton may not require property owners to live on the property to rent an ADU.

Critical Areas Ordinance (CAO) and Shoreline Master Program

Renton has significant critical areas that affect ADU siting:

• Cedar River: A salmon-bearing stream critical for Puget Sound Chinook salmon recovery. Cedar River buffers (often 50–100+ feet) restrict construction near the river
• Lake Washington Shoreline: Regulated by both Renton's CAO and the Shoreline Master Program (SMP) under Washington's Shoreline Management Act. Shoreline jurisdiction typically extends 200 feet upland from the ordinary high water mark
• Wetlands: Black River area and other low-lying areas contain regulated wetlands
• Steep slopes: Hillsides above the valley floor may have landslide hazard designations

Check Renton's GIS mapping system to identify any CAO or shoreline regulations applicable to your property before designing an ADU.

Seismic Hazard

Renton and the Puget Sound region face significant earthquake risk from the Cascadia Subduction Zone (CSZ). The Cedar River valley and Lake Washington shoreline areas have alluvial and fill soils susceptible to liquefaction. Washington DNR and USGS seismic hazard maps identify high-risk areas. ADU foundations in these areas should be designed with geotechnical input. All construction must meet Washington State Building Code seismic requirements.

Permit Process

1. Research your property's zoning, CAO constraints, and shoreline jurisdiction via Renton's GIS portal
2. Consider a pre-application conference with Renton's Planning Division for waterfront or constrained sites
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application at rentonwa.gov or in person at 1055 South Grady Way
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Renton Permit Center: (425) 430-7200 | rentonwa.gov

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