Accessory Structures in Summit County, UT (2026)

ADU Rules

Summit County regulates Accessory Dwelling Units (ADUs) under two separate development codes: the Snyderville Basin Development Code (Title 10 of the Summit County Code), which governs the unincorporated west side of the county around Park City (Kimball Junction, Pinebrook, Jeremy Ranch, Silver Creek, Promontory), and the Eastern Summit County Development Code, which governs the rural east side around Coalville, Henefer, Oakley, Kamas and Francis. Section 10-8-5 of the Snyderville Basin Code caps standalone or attached ADUs at 1,000 square feet, allows only one ADU or one Internal ADU (IADU) per lot (never both), requires the ADU to share the lot with a single-family detached dwelling, and treats the ADU as a Conditional Use in some zones. Park City Municipal Corporation, the incorporated city inside the county, has its own Land Management Code (LMC) Title 15 with separate accessory apartment rules (LMC 15-4-7) requiring 280-1,000 sf, owner occupancy, a recorded Notice to Purchaser, and a strict prohibition on rentals shorter than 90 days. State law (Utah Code Sections 10-21-303 and 17-80-303, originating in 2021's H.B. 82) preempts certain local IADU regulations in primary residential zones countywide.