Idaho Falls, ID Accessory Structures: ADU Rules (2026)

Idaho has no statewide ADU mandate, so accessory dwelling units in Idaho Falls are governed entirely by the city's own Title 11 Comprehensive Zoning ordinance. Following a 2022 ordinance change, the city allows ADUs in the RP and R1 low-density residential zones and the RMH medium-density zone. The maximum size of an accessory dwelling is 750 square feet. A detached ADU must meet the same side yard requirement as a primary structure and keep a minimum setback of twelve feet (12') from the rear property line, except when adjacent to a public or private alley at least sixteen feet (16') wide. Only one ADU is permitted per lot, and it cannot be sold separately or converted to a different form of ownership from the principal dwelling. The property owner must occupy either the principal dwelling or the ADU as their primary residence, enforced through a deed restriction recorded with the Bonneville County Recorder. One additional off-street parking space is required for the ADU beyond the principal dwelling's minimum; a driveway may satisfy this. Recreational vehicles are prohibited from being used as ADUs, and a garage cannot be converted into an ADU unless the required parking is provided elsewhere on the lot.