Renton, WA Accessory Structures: ADU Rules (2026)

Renton Municipal Code 4-2-115 and RMC 4-2-110 (residential development standards) govern Accessory Dwelling Units (ADUs), updated to comply with Washington House Bill 1337 (2023, effective July 2023, codified in RCW 36.70A.681 and related statutes). The state mandate requires cities planning under the Growth Management Act to allow at least 2 ADUs per single-family lot by right — Renton complies by permitting one attached ADU and one detached ADU, or two attached units, on lots with existing or proposed single-family homes. Maximum ADU size in Renton is 1,000 square feet of gross floor area (1,200 square feet allowed on larger lots with meeting certain design criteria). Owner-occupancy requirements have been removed per HB 1337. Off-street parking cannot be required for ADUs within one-half mile of major transit stops (such as South Renton Transit Center, Sounder station, and frequent bus routes). Standard setbacks apply: 5-foot side/rear for detached ADUs, 20-foot front. Height limit is typically 24 feet (may be higher in some zones). Design standards include matching primary dwelling architectural style. Permits required: building, plumbing, electrical, and mechanical. Impact fees have been reduced or waived for ADUs per city council action to encourage middle housing.