ADU Rules in Kent, Washington

Kent (population ~135,000) is one of the largest cities in King County and an important manufacturing, warehousing, and logistics hub in the Green River Valley between Seattle and Tacoma. Kent is one of Washington's most ethnically diverse cities and home to major Boeing operations. The Green River Trail — a regional recreational corridor — runs through the city. Kent is subject to Washington's statewide ADU reform laws that apply to all cities in the state.

Washington State ADU Law: HB 1337 (2023)

Washington HB 1337 (2023) is the controlling statewide ADU law for Kent and all Washington cities. Its 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 Kent to allow duplexes and middle housing in residential zones.

Kent is subject to the Washington Growth Management Act (GMA) and has a comprehensive plan with an Urban Growth Area. King County coordinates growth planning with Kent and other county cities.

Kent Local ADU Code

Kent's Community & Economic Development Department administers zoning and building permits locally. Local ADU regulations must comply with 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 an existing garage, basement, or other space within the primary structure

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

Size Limits

HB 1337 prohibits Kent from requiring ADUs smaller than 1,000 square feet. Confirm current maximum size limits with Kent's Permit Center for your specific zoning district.

Setbacks

State law limits Kent's ability to impose setbacks that would prevent reasonable ADU construction. Setback requirements vary by zone. Verify current standards with the Permit Center before beginning design.

No Owner-Occupancy Requirement

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

Critical Areas Ordinance (CAO)

Kent's CAO protects the Green River and its tributaries (including Big Soos Creek and other salmon-bearing streams), wetlands in the valley floor, frequently flooded areas, steep slopes on the east and west valley walls, and seismically hazardous areas. The Green River valley floor has significant FEMA-mapped floodplains. CAO buffers from streams and wetlands can restrict ADU siting. Kent's GIS mapping system identifies CAO-regulated features — check your property early in the planning process.

Flood Zone Considerations

Much of Kent's flat valley floor is subject to Green River flooding and is mapped in FEMA flood zones. Properties in Special Flood Hazard Areas (SFHAs) face strict building requirements including elevated foundations, which adds cost and complexity to ADU construction. Kent participates in the National Flood Insurance Program (NFIP). Verify your property's flood zone status at msc.fema.gov.

Seismic Hazard

Kent and the greater Puget Sound region face significant earthquake risk from the Cascadia Subduction Zone (CSZ). Kent's Green River Valley has alluvial soils highly susceptible to liquefaction during strong shaking. USGS and Washington DNR seismic maps identify liquefaction-prone areas in the valley. ADU foundations on valley-floor lots should include geotechnical review. All construction must meet Washington State Building Code seismic requirements.

Permit Process

1. Check your property's zoning, flood zone, and CAO status using Kent's online GIS system
2. Contact Kent's Permit Center for pre-application guidance
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application online at kentwa.gov/permits or in person at 220 Fourth Avenue South
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Kent Permit Center: (253) 856-5200 | kentwa.gov/permits

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