La Mesa, CA Accessory Structures: ADU Rules (2026)

Section 24.05.020(D)(8) sets La Mesa's accessory dwelling unit standards. One attached or one detached unit is allowed with an existing or proposed dwelling on single-family or multifamily zoned lots, capped at one thousand two hundred square feet of floor area. Lots of ten thousand square feet or less with an existing single-family residence get an additional five percent of lot coverage just for the ADU. Setbacks generally track the primary dwelling's zone standards, but the code sets a floor: not less than four feet from side and rear property lines or adjacent access easements, even where the underlying zone would otherwise demand more, unless the zone allows something smaller.

No lot-coverage limit, front setback, open-space rule or minimum lot size can block an ADU of at least eight hundred square feet built with four-foot side and rear setbacks. Four categories of ADU, covering conversions of existing space, new detached units at least eight hundred square feet, multifamily conversions of non-livable space, and up to two detached units on multifamily lots, must be approved ministerially, without discretionary review or a hearing, within sixty calendar days. New or additional parking is never required for an ADU, and removing a garage or carport to build one does not require replacing those spaces.

ADUs do not need fire sprinklers if the primary residence lacks them, and rentals must run longer than thirty days. A companion junior accessory dwelling unit, capped at five hundred square feet and built inside the existing home, is allowed on the same lot under Section 24.05.020(D)(9).