Twain Harte, CA Accessory Structures: ADU Rules (2026)

California Government Code §65852.2 preempts local ADU bans and sets minimum standards that Tuolumne County codified in Ordinance Code Chapter 17.36 (adopted 2020). On a single-family lot, the County must allow one ADU and may also permit a Junior ADU (JADU, max 500 sq ft inside the existing primary dwelling per §65852.22) if the property is owner-occupied. ADU floor area generally ranges from 150 sq ft minimum up to 800 sq ft for a one-bedroom unit, with larger sizes allowed under state law and the County's development standards. Detached ADUs are limited to 16 feet in height; ADUs attached to the primary residence may reach 25 feet. Minimum setbacks are 4 feet from rear and interior side property lines for new construction; conversions of existing legal structures are exempt from setback requirements. Parking is capped at one space per bedroom and is waived entirely if the parcel is within one-half mile walking distance of public transit. No replacement parking is required when a garage or carport is demolished or converted to create an ADU. Per Gov. Code §65852.2(f)(3), ADUs under 750 sq ft are exempt from local impact fees, and fees on larger ADUs must be proportional. The County must approve or deny a complete ADU application within 60 days (ministerial review). Twain Harte sits in a designated High or Very High Fire Hazard Severity Zone, so ADUs must also meet Chapter 7A of the California Building Code (ignition-resistant construction).