El Cajon, CA Accessory Structures: ADU Rules (2026)

180 governs both accessory and junior accessory dwelling units on any lot zoned for single-family or multifamily use. Subsection A requires a building permit for any new ADU or JADU, but the process is ministerial once the objective standards are met, with no discretionary hearing. On a single-family lot, an owner may add up to one ADU and one JADU alongside the existing or proposed primary home. Multifamily lots get a separate allowance: at least one unit, and up to 25% of the existing unit count, may be converted from non-livable space such as storage rooms, basements, garages or attics, and a proposed multifamily project may add up to two detached ADUs subject to four-foot side and rear setbacks at a 16-foot height, or three-foot setbacks at 12 feet; an existing multifamily property may add up to eight detached ADUs, or one per primary unit, whichever is fewer.

Size is capped at 1,200 square feet of habitable space for an attached or detached ADU, and a junior ADU tops out at 500 square feet, contained entirely within the existing single-family structure. Detached units built outside the primary dwelling's setback area get graduated height limits: 20 feet with a five-foot setback, 16 feet with four feet, or 12 feet with three feet, dropping to 18 feet within a half mile of a major transit stop. Parking is one additional space per ADU unless the unit sits within a half mile of transit, in a historic district, is a JADU, or several other listed exceptions apply.

No lot coverage or open space limit can block an ADU permitted under Government Code § 66323, and no fire sprinklers are required unless the primary home already has them.