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

Glenn County's Unified Development Code (Title 15) regulates ADUs as 'second dwellings.' Chapter 15.175 establishes the permitting procedure: a second-dwelling application is filed with the planning authority, must meet the standards in Chapter 15.590 (Minimum Residential Construction Standards), and is approved once the Planning Director determines it complies. Section 15.590.020(B) requires second units to be on a permanent foundation, to have an entrance separate from the primary dwelling, and provides that the off-street parking requirement of Chapter 15.610 is waived where there is insufficient space for an additional vehicle. The code states that, per California Government Code Section 65852.2(a)(1)(B)(i), no maximum size is imposed on a second dwelling so long as it does not exceed lot coverage requirements. The Title 15 text dates to 2018 and cites the older Section 65852.2. State ADU law has since been recodified into Government Code Sections 66310-66342 (effective January 1, 2025). Under that controlling state law, an ADU and a junior ADU (JADU) must be approved ministerially; a 'state-exempt' ADU under Section 66323 must be allowed at up to 800 square feet and 16 feet in height with 4-foot side and rear setbacks regardless of local lot-coverage or design standards, and a JADU is limited to 500 square feet within an existing single-family residence. Where the county's older ordinance conflicts with current state law, state law preempts. Owners should confirm requirements with Glenn County Planning & Community Development Services.