Accessory Structures in Summit County, CO (2026)

ADU Rules

Unincorporated Summit County (the resort corridor outside Breckenridge, Dillon, Frisco, and Silverthorne town limits) allows accessory dwelling units in most residential zoning districts under the Summit County Land Use and Development Code, subject to a recorded restrictive covenant requiring the occupant of either the ADU or the primary residence to work in Summit County at least 30 hours per week on average. Summit County has deed-restricted ADUs to the local workforce since 1984. The approval process has been streamlined to require only a building permit in most cases (no separate planning approval), although Class 2 planning review is still triggered on duplex lots and in PUDs that specify it. The County waives all county-administered fees (building permit, planning, engineering) for at least 10 years if the covenant is honored, and the Summit County Housing Department's ADU Assistance Program reimburses up to 25% of construction cost. Inside the Town of Breckenridge, the Town's Development Code Policy 51 (Section 9-1-19-51A) caps an ADU at the lesser of one-third the density of the primary unit or 1,200 square feet, with its own Town deed restriction. Summit County is a mountain county outside any of Colorado's five metropolitan planning organizations, so HB24-1152 (the 2024 statewide ADU law effective June 30, 2025) does not preempt local rules here.