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

Plumas County's Board of Supervisors adopted an ADU ordinance (introduced April 16, 2024) adding Article 45 to Title 9, Chapter 2 of the County Code. Attached, detached, and conversion ADUs and junior ADUs are permitted in any zone where a dwelling unit is allowed (Sec. 9-2.4502). On a single-family parcel the county permits one attached or conversion ADU, one detached new-construction ADU, and one JADU (Sec. 9-2.4505(a)). A detached ADU may not exceed 1,200 sq ft; an attached ADU is capped at 50 percent of the primary dwelling's living area or 800 sq ft, whichever is greater, but never more than 1,200 sq ft (Sec. 9-2.4505(c)). The ordinance guarantees a 'statewide exemption ADU' of up to 800 sq ft, 16 ft in height, with 4-foot side and rear setbacks that cannot be prohibited (Sec. 9-2.4505(b)). Maximum height is 35 ft; side and rear setbacks are 4 ft (none for conversions of existing structures) (Secs. 9-2.4505(d)-(e)). The Building Department must approve or deny a complete ministerial application within 60 days or it is deemed approved (Sec. 9-2.4504). New detached ADUs must install a solar PV system; ADUs are exempt from impact fees. These provisions implement Government Code 66310-66342 (recodified in 2025 from former 65852.2), which preempts more restrictive local rules and is relevant to Dixie Fire rebuilds and rural ranch parcels.