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

ADUs in unincorporated Tuolumne County are governed by the County's Title 17 (Zoning) ADU chapter, which the County rewrote to comply with state law. Before the 2020-era update, ADUs (then called second units) were regulated under Tuolumne County Ordinance Code Section 17.52.200; the County's Accessory Dwelling Unit Ordinance project then reorganized that chapter to allow ADUs ministerially wherever single-family and multifamily residential uses are permitted, to allow junior ADUs (JADUs), and to clarify code-enforcement provisions. Because California's ADU statutes (relocated by SB 477 from Government Code Section 65852.2 into Government Code Sections 66310-66342, effective 2024) preempt conflicting local rules, the County must permit a detached ADU of at least 800 square feet at a height of at least 16 feet with 4-foot side and rear setbacks. Per state standards reflected in County practice, detached new-construction ADUs may reach 16 feet, attached ADUs up to 25 feet, and conversions of existing space have no added height or setback requirement. ADUs created entirely within an existing structure require no setback, and a limited 150-square-foot expansion is allowed where needed for ingress and egress. Required parking may not exceed one space per bedroom and is waived within one-half mile of transit. The County's draft ordinance limited rentals of all ADU types to terms of 30 days or longer (not retroactive to previously permitted units). Separate septic systems are not required by state law. Building permits for ADUs are reviewed ministerially.