ADU rules in Rancho Cucamonga

Detached ADUs are allowed on every lot zoned for single-family or multifamily use with an existing or proposed home: 17.100.020 applies Chapter 17.100 to all such lots, Table 17.30.030-1 lists Accessory Dwelling Unit as P (permitted by right) in the VL, L, LM, M, MH and H residential zones, Hillside Residential (HR) and Open Space Conservation (OSC), and Table 17.136.020-1 permits them in all eleven form-based zones of Article VIII (they are not permitted in the Neo-Industrial, Industrial Employment, Parks and Flood Control/Utility Corridor zones). Chapter 17.100, restated in full by Ord. No. 1049 (adopted December 3, 2025, effective January 2, 2026), offers the Gov. Code 66323 'Category 2' unit (one new detached ADU of up to 800 sq ft with 4-foot side and rear setbacks on a single-family lot, combinable with a JADU) and a locally regulated detached ADU of up to 1,200 sq ft under 17.100.060. On multifamily lots, 'Category 4' allows up to eight detached ADUs with an existing building (never more than its existing unit count) or two with a proposed one. A Bonus ADU program (17.100.050, a Prohousing Designation commitment) allows one additional attached, detached or converted ADU on single-family lots of at least 20,000 sq ft, reviewed ministerially.

Attached and conversion ADUs are allowed on the same lots. 'Category 1' (17.100.040.A, tracking Gov. Code 66323(a)(1)) allows one ADU within the existing or proposed space of a single-family home or an existing accessory structure, with up to 150 sq ft of expansion limited to ingress and egress, plus one JADU; 'Category 3' allows at least one ADU, and up to 25 percent of the existing unit count, in non-livable space of an existing multifamily building such as storage rooms, attics, basements or garages. New attached additions under the local standards may reach 50 percent of the main home or 1,200 sq ft, whichever is less, and 25 feet in height (Table 17.100.050-1). JADUs of 220 to 500 sq ft must sit entirely within the walls of a single-family home (attached garages count as part of the home), need their own exterior entry and an efficiency kitchen, and are not allowed in accessory structures (17.100.070).

Table 17.100.050-1 in 17.100.060.F caps locally regulated ADUs at 1,200 sq ft detached and, for attached units, at 50 percent of the main dwelling or 1,200 sq ft, whichever is less, with minimum sizes of 350 sq ft detached and 220 sq ft attached; garages and other optional accessory structures do not count toward the cap. Heights are 16 feet for detached units, 18 feet (or 20 feet to match the main roof pitch) within half a mile of a major transit stop or high-quality transit corridor, 18 feet on a lot with a multistory multifamily building, 25 feet for attached units, and the zone's limit for an ADU built above a garage. The state-exempt Category 2 detached unit is capped at 800 sq ft and 16 feet (18 feet near major transit, plus 2 feet to match the roof pitch), JADUs at 500 sq ft, and lot coverage and front setbacks yield where they would block an 800 sq ft, 16-foot ADU with 4-foot side and rear setbacks (17.100.060.G, H.2). The local text has no such floor for the 50 percent attached cap, but Gov. Code 66321(b)(3) forbids a percentage-based limit that does not allow at least 800 sq ft of interior livable space and 66325 makes the state article supersede conflicting local text, so an attached ADU on a home smaller than 1,600 sq ft may still reach 800 sq ft.

No for ADUs: Chapter 17.100 imposes no owner-occupancy condition on an ADU, and Gov. Code 66315 bars one. For JADUs, 17.100.090.C (Ord. No. 1049) still requires the owner to live in the rest of the home or in the JADU in every case, exempting only a governmental agency, land trust or housing organization owner. Since January 1, 2026, Gov. Code 66333(b) as amended by AB 1154 allows that condition only where the JADU shares sanitation facilities with the house, and 66339.5(a) makes the state JADU article supersede a conflicting local ordinance, so a JADU with its own bathroom carries no owner-occupancy requirement. Ord. No. 1049 was adopted December 3, 2025, after AB 1154 was chaptered (Stats. 2025, ch. 507) but before it took effect, and HCD's December 5, 2025 technical assistance letter to the city listed exactly this change; the city's May 2024 handbook also states a JADU owner-occupancy requirement without the sanitation distinction.

New detached ADUs built under the local standards must provide one off-street space (17.100.060.I.1), which may be tandem, in an enclosed garage or in setback areas; a space in a garage shared with the main home must be walled off with its own door, and access must use the main dwelling's driveway unless the lot has alley or permitted corner-lot access. No space is required within a one-half mile walk of public transit (any bus stop or train station), in an architecturally and historically significant district, for a unit that is part of the existing or proposed home or an existing accessory structure, where on-street permits are required but not offered, within one block of a car-share station, or when the ADU is filed with a new home (17.100.060.I.5, mirroring Gov. Code 66322(a)). The text sets no requirement for attached additions, the state-exempt units of 17.100.040 or JADUs (17.100.070.F), and one space per unit is the Gov. Code 66314(d)(10) ceiling. Garage, carport or covered spaces lost to an ADU need not be replaced (17.100.060.I.4); Gov. Code 66314(d)(11) extends that to uncovered spaces and carries no 'as long as the ADU remains in use as a legal ADU' qualifier.

Every ADU and JADU needs only a building permit checked against the Building Standards Code, Gov. Code Chapter 13 and Chapter 17.100 (17.100.030.A), and Table 17.30.030-1 lists ADUs as P, permitted by right. The city must approve or deny within 60 days of a complete application (17.100.030.B, whose citation to 'Government Code Section 63317' is a typo for 66317), no minor exception may be granted or even accepted for processing (17.100.030.C), an ADU filed with a home that needs discretionary review is decided separately without discretionary review or a hearing (17.100.030.D), and Bonus ADUs are ministerial too (17.100.050.D). Detached ADUs using a city-preapproved plan must be decided within 30 days (17.100.030.E), and Resolution No. 2026-024 (April 15, 2026) set a $1,363 plan-review fee for preapproved ADU plans against $2,063 for a standard ADU of up to 1,200 sq ft. State law adds the 15-business-day completeness determination and a written appeal to the governing body or planning commission decided within 60 business days (Gov. Code 66317(a)(2), (d)), which the local text does not restate. In the Hillside Overlay Zone or on slopes of 8 percent or more, 17.16.140 routes projects through hillside development review and its small-project exception excludes ADUs; Gov. Code 66317(a)(1) and (c) confine ADU review to objective, ministerial standards (see caveats).

ADUs may be rented, but 17.100.090.B requires any rental of an ADU or JADU to run longer than 30 consecutive days, which Gov. Code 66315 permits and 66323(e) and 66333(g) require for state-exempt units and JADUs. Citywide, Chapter 8.34 (Ord. No. 969, 2020) allows short-term rentals only as hosted or un-hosted stays at the host's primary residence under a city permit ($201 application fee on the city's page), business license and transient occupancy tax certificate; vacation rentals are prohibited, un-hosted stays are capped at 90 days a year, and 8.34.090.G separately bars short-term use of an ADU bound by a covenant against rentals of 30 days or less. Separate sale of an ADU is prohibited except under the qualified-nonprofit tenancy-in-common path of Gov. Code 66341 (17.100.090.A). The city has not adopted a Gov. Code 66342 ADU-condominium ordinance, and 17.100.090.A.6 says the section 'does not imply' a condominium sale is allowed outside those nonprofit conditions.