Building an ADU in Rancho Cucamonga

Which rules apply in Rancho Cucamonga

The rules are in Chapter 17.100 of the Development Code, adopted as Ordinance No. 1049 on December 3, 2025. They apply to all lots zoned for single-family or multifamily homes, including mixed-use zones.

The city's ADU Handbook is dated May 2024, before the new ordinance. Some of its numbers are now out of date. For example, it gives attached ADUs a height limit of the house's height or 16 feet, whichever is higher (the code now says 25 feet), and it limits apartment lots to two detached ADUs (the code now allows up to eight). The handbook itself says that where it and the Municipal Code differ, "the standards found in the Municipal Code shall prevail."

State law sets the floor for what any California city must allow; see our California page. [1][3]

What you can build

Chapter 17.100 starts with the four kinds of ADUs that state law makes cities approve under simpler rules:

• Converted ADU and JADU: one ADU and one JADU on a lot with a single-family home, inside the house or an existing accessory structure. A converted accessory structure can grow by up to 150 sq ft for entry and exit.
• New detached ADU: one detached ADU of up to 800 sq ft with 4-foot side and rear setbacks, 16 feet tall (18 feet near major transit, plus 2 feet to match the roof pitch). It can be combined with a JADU.
• Apartment conversions: at least one ADU, and up to 25% of the units, in non-living space of an existing apartment building, such as storage rooms, attics, basements or garages.
• Detached ADUs at apartment buildings: up to eight on a lot with an existing apartment building (no more than the number of units), or two with a proposed one.

The code says the new detached ADU "may be combined with a JADU." HCD's handbook goes further: it says cities must let these categories be combined, so a single-family lot can have a converted ADU, a new detached ADU and a JADU. Ask Planning how the city applies this to your lot.

Big lots. On a lot of at least 20,000 sq ft with a single-family home, you can add one more ADU, attached, detached or converted. It must meet the full development standards below and is approved without a hearing.

ADUs that don't fit those categories, such as a detached ADU over 800 sq ft, follow the development and design standards in the rest of the chapter. [1][4]

Size, height and setbacks

For ADUs outside the state's four categories, Table 17.100.050-1 of the code sets:

• Attached ADU: 220 sq ft minimum; maximum is 50% of the house or 1,200 sq ft, whichever is less; up to 25 feet tall.
• Detached ADU: 350 sq ft minimum, 1,200 sq ft maximum. Height is 16 feet, or 18 feet within a half mile of a major transit stop or high-quality transit corridor (20 feet to match the house's roof pitch). On a lot with a multi-story apartment building it's 18 feet.
• Above a garage: no taller than the zone's height limit.
• Setbacks: at least 4 feet from side and rear lot lines. The front setback follows the zone, unless that would block an 800 sq ft ADU that is 16 feet tall with 4-foot side and rear setbacks. No setback is needed for an ADU inside an existing structure or rebuilt in the same place and size.
• Lot coverage: the zone's limit applies, except where it would block that same 800 sq ft ADU.
• Facilities: an ADU needs its own entrance, kitchen and bathroom. It may have its own meters, and doesn't need fire sprinklers unless the house requires them.

HCD's handbook says a city's minimum size can't rule out an efficiency unit, which can be as small as 150 sq ft. Rancho Cucamonga's minimums are 220 sq ft (attached) and 350 sq ft (detached), so ask Planning if you want a smaller unit. [1][4]

Parking and garage conversions

A newly built detached ADU needs one parking space, which can be tandem, in a garage or in a setback area. If the space is in a garage shared with the house, it must be walled off with its own garage door. The ADU must generally use the same driveway as the house, and a driveway to required parking must be at least 10 feet wide.

No parking is required when the ADU is:

• within a half-mile walk of public transit, such as a bus stop or train station,
• in an architecturally and historically significant district,
• part of the house or an existing accessory structure,
• where on-street parking permits are required but not offered to the ADU occupant,
• within one block of a car-share station, or
• applied for together with a new home on the same lot and meets one of the cases above.

A JADU needs no parking. If you convert or demolish a garage, carport or covered parking to build an ADU, you don't have to replace those spaces "as long as the ADU remains in use as a legal ADU." See our garage conversion guide. [1]

Design standards

ADUs and JADUs outside the state's four categories that are in the front yard, next to the house, or visible from the street must meet these design standards:

• The roof and walls must have substantially the same color, material and texture as the house.
• Exterior stairs can't be visible from a public street (alleys and trails excepted), other than steps from the ground to the first floor.
• Driveways and walkways can't take up more than 50% of the front yard.
• Properties listed on the California Register of Historical Resources may need additional design considerations, and an ADU or JADU on a property under a Mills Act contract must follow the Mills Act guidelines.

[1]

Fees

The city's fee schedule for fiscal year 2026-27 (effective July 1, 2026) lists these Building and Safety fees for residential new construction, including mechanical, electrical and plumbing:

• R3 Accessory Dwelling Unit: $1,822 up to 500 sq ft, plus $44 for each additional 100 sq ft, and $2,715 at 2,500 sq ft.
• Pre-Approved ADU Plan: $1,363, up to 1,200 sq ft.
• Processing: $343 for a routed residential permit.

Building fees are subject to an additional 12% technology fee and/or a 10% General Plan Maintenance Fee unless the schedule says otherwise.

Other agencies may review the plans or charge fees before the city issues a permit. These include the Cucamonga Valley Water District, Rancho Cucamonga Municipal Utility, Southern California Edison, SoCalGas, the Fire District, your HOA, and the local school districts.

Under state law, an ADU with 750 sq ft of interior livable space or less pays no impact fees, and a larger one pays in proportion to the size of the house. ADUs under 500 sq ft don't pay school impact fees. For typical building costs see our ADU cost guide. [4][5][6]

How long it takes

The code says an ADU or JADU application "shall be approved or denied within 60 days after the city receives the completed application." An application using a pre-approved detached ADU plan must be approved or denied within 30 days. Minor exceptions from the ADU rules aren't allowed.

State law also requires a written completeness decision within 15 business days. The city's handbook says to expect at least two rounds of comments, with several weeks for each round. See our ADU permit process guide. [1][3][4]

Junior ADUs

A JADU is 220 to 500 sq ft, not counting a shared bathroom, entirely within the walls of a single-family home, which can include an attached garage. JADUs aren't allowed in detached accessory buildings. It needs its own exterior entrance and an efficiency kitchen with a cooking appliance, counter and storage. If it shares a bathroom with the house, it needs an interior entry too. See our junior ADU guide.

Owner occupancy. The code says the owner "must reside in either the remaining portion of the primary dwelling or in the newly created JADU." Since 2026, state law requires that only when the JADU shares bathroom facilities with the house. Ask Planning how the city applies the rule to a JADU with its own bathroom. [1][4]

Renting, selling and unpermitted units

You don't have to live on the property to have an ADU. Any rental of an ADU or JADU must be for more than 30 consecutive days, so short-term rentals aren't allowed. An ADU can't be sold separately from the house unless a qualified nonprofit built the ADU or the house and the other conditions listed in the code, such as affordability restrictions, are met.

Unpermitted units. For an ADU or JADU built without permits before January 1, 2020, the city won't deny a permit because it doesn't meet building or ADU standards. The exception is when a fix is needed for health and safety. You won't pay impact fees or connection charges to legalize it, except in limited cases. You can get a confidential inspection from a licensed contractor first. [1][3]

Permit steps in Rancho Cucamonga

1. Talk to Planning about your lot

   Email Planning@CityofRC.us or call 909-477-2750 to discuss options and site issues such as slopes, septic systems or existing accessory structures. [3][7]

2. Check septic, fire and solar rules

   If you're on septic, check with Building and Safety early; projects within 300 feet of an existing sewer must connect to it. Lots in the Wildland-Urban Interface Fire Area need a defensible-space landscaping plan, and new detached ADUs generally need solar. [3]

3. Prepare plans

   Use the city's residential submittal requirements for ADUs. Depending on the ADU's type, size and height, Planning may also need to clear the plans. [3][6]

4. Apply online

   Create your building permit application in the Online Permit Center. Building and Safety takes all plan submittals electronically and doesn't issue permits over the counter. [2]

5. Respond to plan check and other agencies

   Expect at least two rounds of comments. Water, utility, fire and school agencies, and your HOA, may also need to review the plans or collect fees. [3][6]

6. Pay fees and get the permit

   Permits are issued by email through the permit technicians at EDRnotification@CityofRC.us and the Online Permit Center. [2]

7. Build and pass inspections

   For inspection questions, text (909) 303-1786 or call (909) 477-2710. [2]

Who to call

• Rancho Cucamonga Planning Division

  ADU eligibility and zoning questions (Planning@CityofRC.us)

  909-477-2750

  10500 Civic Center Drive, Rancho Cucamonga, CA 91730

  [7]

• Rancho Cucamonga Building and Safety

  Permits and plan check (EDRnotification@CityofRC.us; text for quick questions)

  (909) 488-4668

  10500 Civic Center Drive, Rancho Cucamonga, CA 91730

  [2]

• Rancho Cucamonga building inspections

  Inspection questions (or text (909) 303-1786)

  (909) 477-2710

  [2]

Questions people ask