Antioch, CA Accessory Structures: ADU Rules (2026)

1 and 18007. An ADU is defined as an attached or detached residential dwelling unit that provides complete independent living facilities, located on a lot with a proposed or existing primary residence or located in the IH Overlay District. Detached ADUs may be up to 1,200 square feet of floor area; attached ADUs may be the lesser of 50% of the primary dwelling's living area or 1,200 square feet; and JADUs are capped at 500 square feet and must be created within the walls of an existing or proposed single-family residence.

A new-construction detached ADU on a single-family lot must observe a minimum four-foot setback from the rear and interior side property lines, and a height of up to 16 feet is allowed for a detached ADU. If the site is within one-half mile walking distance of a major transit stop or a high-quality transit corridor, the detached ADU may be up to 18 feet by right (and up to 20 feet if necessary to match the roof pitch of the primary dwelling). Attached ADUs may go up to 25 feet.

Required parking may not exceed one space per bedroom, and parking is fully exempt for JADUs, for ADUs created within an existing structure, for sites within one-half mile of public transit, in historic districts, and where on-street parking permits are required. ADUs constructed on or after January 1, 2020 are not subject to any owner-occupancy requirement; JADUs remain subject to the state-law requirement that a natural person with legal or equitable title occupy either the primary dwelling or the JADU. Antioch processes ADU permits ministerially with a 60-day review clock and offers Pre-Approved ADU Plans through the Community Development Department to expedite design review.