Downey, CA Accessory Structures: ADU Rules (2026)

06 makes ADUs and JADUs a permitted use in the City's residential zones, R-1, R-2, R-3, R-3-O, and M-U, wherever an existing or proposed single-family or multifamily dwelling sits, consistent with the General Plan designation for the lot. JADUs are barred on multifamily-zoned property. 08(a)(1) allows up to two ADUs, which can combine one newly built attached or detached unit with one converted from existing non-livable space, plus a single JADU converted from existing space, capped at 500 square feet, with its own exterior entrance.

08(b)(1)-(2) cap a studio or one-bedroom ADU at 850 square feet and a two-or-more-bedroom unit at 1,000 square feet, though an attached ADU is further limited to 800 square feet or 50% of the primary home's floor area, whichever is more. 08(b)(3)-(4). 08(c)(1) require a minimum of four feet to the side and rear property lines for new construction, with narrow exceptions letting an 800-square-foot ADU encroach into the front setback if plans document that placing it elsewhere on the lot is physically infeasible. 08(d) caps a detached ADU at 16 feet, rising to 18 feet (or 20 feet with a matching roof pitch) within a half-mile of a major transit stop, while an attached ADU can reach 25 feet or the zone's height limit, whichever is lower, but never more than two stories.