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

Mariposa County's Planning Department states plainly: 'Currently Mariposa County does not have its own ordinance to dictate the rules for ADUs and therefore defers to the state law.' A local Development Code update that would adopt county ADU standards is still in progress. Until then, State ADU Law controls. Because the County has no compliant local ordinance, the state default maximum size applies: up to 1,200 sq ft of interior livable space for a new detached ADU (Gov. Code 66314(d)(4)), and an attached ADU up to 50% of the primary dwelling's floor area, but always allowing at least 800 sq ft. A four-foot side and rear setback is the maximum the County may require (Gov. Code 66314(d)(7)), and no setback may be required for an ADU created within an existing structure. State law sets no maximum height, but a local agency cannot limit a detached ADU to less than 16 feet. Under Gov. Code 66323, a property with a single-family home may add one converted ADU, one detached ADU (up to 800 sq ft), and one JADU. Owner-occupancy cannot be required for ordinary ADUs (Gov. Code 66315). Apply through the County's online permitting system.