ADU rules in Rancho Santa Margarita

A detached ADU is a principal permitted use (P) in every residential district (RL, RLM, RM and RH in Table 9.03.2), in the Mixed-Use district and in the Workforce Housing Overlay, and Sec. 9.04.190(d)(1) allows ADUs on any lot zoned for single-family or multifamily use that holds a proposed or legally developed dwelling. A single-family lot may carry one detached new-construction ADU in addition to one attached or converted ADU and one JADU; a lot with an existing multifamily building may add up to eight detached ADUs (never more than its existing unit count), and a lot with a proposed multifamily building up to two. Ord. No. 25-03 (adopted 10-8-2025) restated the section and added ADUs to the RH column of the use table.

Attached ADUs (additions) and converted ADUs inside the home, an attached garage or an accessory structure are allowed by right on the same lots, one attached or converted ADU plus one JADU per single-family lot, and on existing multifamily buildings at least one and up to 25 percent of the existing unit count in non-livable space such as storage rooms, attics, basements or garages. An attached or converted ADU needs independent exterior access. JADUs (150 to 500 sq ft) must sit within the walls of a proposed or existing single-family home, an attached garage included, on a lot zoned for single-family use.

Sec. 9.04.190(e)(4) caps a detached ADU at 1,200 sq ft of total floor area and an attached ADU at the lesser of 1,200 sq ft or 50 percent of the existing primary dwelling, but never so low that an 800 sq ft unit is barred; converted ADUs that add no floor area are uncapped, and an accessory-structure conversion may add up to 150 sq ft for ingress and egress. The minimum is 150 sq ft, and JADUs run 150 to 500 sq ft. A detached unit may be 16 ft tall, 18 ft within one-half mile walking distance of a major transit stop or high-quality transit corridor (plus 2 ft to match the main roof pitch) or on a lot with a multistory multifamily building; an attached unit may reach the zone height or 25 ft, whichever is lower, and two stories. Lot coverage, floor area ratio, open space, front setback and minimum lot size standards are waived where they would block an 800 sq ft unit (e)(5), and state-exempt detached ADUs on multifamily lots are not held to the 1,200 sq ft cap (h)(6).

Sec. 9.04.190(g)(3)(a) states that owner occupancy of either the primary dwelling or the ADU is not required, consistent with Gov. Code 66315. For JADUs the code still requires the owner to live in the JADU or the main home in every case, through (g)(3)(b) and the deed restriction in (f)(9)(c); since 1-1-2026 Gov. Code 66333(b) allows that condition only where the JADU shares sanitation facilities with the main home and bars it where the JADU has its own bathroom, so the local clause yields for separate-bath JADUs. The recorded JADU deed restriction (one JADU, no separate sale, size and attributes) remains required before the building permit issues.

Sec. 9.04.190(e)(7) requires one off-street space for an attached or detached ADU, which may sit in a setback area or as tandem parking on a driveway, and garage, carport or uncovered spaces removed for an ADU need not be replaced. No space is required within one-half mile walking distance of public transit, in a historic district, for converted ADUs, where on-street permits are required but not offered, within one block of a car-share station, or when the ADU is filed together with a new single-family or multifamily dwelling; (h)(6) excuses state-exempt ADUs under Gov. Code 66323 from (e)(7), and (f)(6) adds no parking for JADUs. The code does not say whether a single-family detached unit larger than 800 sq ft still counts as the state-exempt 66323(a)(2) unit (66323(a)(2)(A) lets a city cap that unit at 800 sq ft of livable space; the city's text neither imposes nor waives the cap), and Gov. Code 66314(d)(10)(A) limits parking to one space per unit or per bedroom, whichever is less, which on a plain reading the one-space rule exceeds for a studio.

An ADU or JADU needs the city's ADU application (Planning Division form and fee) and a building permit; the Development Services Director approves or disapproves a complete application ministerially, without discretionary review or a public hearing, within the time state law allows (Gov. Code 66317: a 15-business-day completeness determination and 60 days to act), and Table 9.08.1 lists ADUs as a Planning Director decision with no hearing. Review is limited to compliance with Sec. 9.04.190, nonconforming zoning conditions need not be corrected, a detached-garage demolition permit is issued with the ADU permit, and state-exempt units under Gov. Code 66323 are approved ministerially without the local standards that state law displaces.

Sec. 9.04.190(g)(2) requires any rented ADU to be let for a term longer than 30 days and prohibits short-term rental of 30 days or less, and (g)(1) lets an ADU or JADU be rented separately but never sold or conveyed apart from the primary residence except under Gov. Code 66341. Ord. No. 25-03 deleted the old JADU short-term-rental bar after HCD's 10-11-2024 finding that state law then set no JADU rental minimum, but Gov. Code 66333(g) (effective 1-1-2026) now requires JADU rentals to run longer than 30 days, as 66323(e) does for state-exempt ADUs; for ordinary ADUs Gov. Code 66315 lets a city require terms of 30 days or longer, so the local rule is one day stricter than that floor. The municipal code has no short-term rental chapter or permit and treats any use not listed in a zone as prohibited (Sec. 9.03.050); the 2024-2025 Orange County Grand Jury report lists Rancho Santa Margarita among the 19 Orange County cities that ban STRs, and the city's 8-14-2025 response agreed with the findings directed at those cities.