Alpine County, CA Accessory Structures: ADU Rules (2026)

The entire county is unincorporated, so Alpine County's Community Development Department reviews all accessory (secondary) dwelling units. Per the county's ADU Information Sheet, Chapter 18.69 of the County Code predates current state law and does not comply, so the county applies state law (Government Code Section 65852.2 for ADUs and 65852.22 for JADUs) until a new ordinance is adopted. A junior ADU is defined as no more than 500 square feet contained entirely within a single-family dwelling, with one allowed per dwelling. New detached ADUs may be up to 1,200 square feet; new attached ADUs may not exceed 50% of the principal dwelling or 800 square feet, whichever is more. Conversions of an existing garage or part of the primary dwelling have no maximum size. New ADUs need at least a 4-foot setback from rear and side property lines; conversions of existing structures need no setback, and front setbacks cannot preclude an 800-square-foot ADU. Parking is one space per unit or per bedroom, whichever is less, and is waived in the Markleeville Historic District. ADUs are permitted in AG, AP, LP, TP, RE, RN, NC, C, INS, and PD zones. New detached units (except HUD-code manufactured homes) require solar panels. Once an application is complete, the county has 60 days to act when a primary dwelling already exists.