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

Modoc County codifies state ADU law at Section 18.100.010(E) of Title 18 (Zoning), which allows accessory dwelling units (ADUs) and junior ADUs (JADUs) in all zones permitting single-family or multifamily residential uses. The County's published ADU comparison table lists the zones where one ADU per site is allowed as LIC, AG, LI, RR, RL, RH and RT. A 'statewide-exemption' ADU may be up to 800 square feet of floor area, no more than 16 feet peak roof height, with side and rear setbacks of at least four feet (the building official and fire chief must confirm the setbacks are sufficient for fire safety). A JADU is no more than 500 square feet, contained entirely within an existing or proposed single-family residence, and must include an efficiency kitchen. On a single-family lot you may add one ADU plus one JADU; lots with existing multifamily structures may convert up to 25 percent of units and add up to two detached ADUs. Applications are considered and approved ministerially, without a public hearing, and the County must act within 60 days of a complete application. Fire sprinklers are required only if required in the primary residence. An ADU may be rented for terms of 30 days or longer but may not be sold separately from the primary dwelling or used as a short-term rental. The County ordinance cites Government Code 65852.1 and 65852.22; the state ADU statute was renumbered to Government Code 66310-66342 by SB 477 in 2024, and the more permissive of County or state standards applies.