Building an ADU in Cupertino

What you can build in Cupertino

Cupertino allows ADUs on lots in any residential or mixed-use residential zone. The lot must already have a single-family home. On a multifamily or mixed-use lot, it needs at least one home. On a vacant lot, you can propose an ADU only together with a new home. The rules are in Chapter 19.112 of the Municipal Code, last amended in 2025. The code says state law prevails if the two conflict.

The code sorts ADUs into two groups:

• Streamlined ADUs follow state law (Gov. Code 66323). These are conversions of space inside your home or an existing accessory building, plus new attached or detached ADUs of 800 sq ft or less with 4-foot side and rear setbacks.
• Non-streamlined ADUs are larger new ADUs. They must meet the lot coverage, floor area and open space rules of your zone.

On a single-family lot, the code allows up to three ADUs in total, in any mix of an attached ADU, a conversion ADU, a detached ADU and a junior ADU. The city's ADU web page still says the limit is two (a detached ADU of 800 sq ft or less plus a JADU), and that a JADU can't be combined with an attached ADU. Confirm the count for your lot with the Planning Division.

On a multifamily lot, you can convert non-living space such as storage rooms, attics, basements or garages: at least one ADU, and up to 25% of the existing units. With an existing multifamily building, you can also add up to eight detached ADUs, but no more than the number of existing units. With a proposed multifamily building, you can add up to two detached ADUs. [1][2]

Size, height and setbacks

Streamlined ADUs (800 sq ft or less). A new attached or detached ADU can be up to 800 sq ft of living space, not counting decks. It needs 4-foot side and rear setbacks. A detached ADU can be 18 feet tall, or 20 feet within a half mile of a major transit stop or high-quality transit corridor if the roof pitch matches the main home. An attached ADU can be 25 feet or the height limit for the main home, whichever is lower. These ADUs are not limited by lot coverage, floor area ratio (FAR) or open space rules.

Conversions. Converting space inside your home or an existing accessory building has no size cap. You may add up to 150 sq ft to an accessory building for an entrance. The conversion can't raise the building's height. Setbacks only need to be enough for fire and life safety.

Larger ADUs (over 800 sq ft). These can be up to 850 sq ft for a studio or one bedroom, or 1,000 sq ft with two or more bedrooms. An attached ADU can't be more than 50% of the existing main home. They count toward your lot's FAR, lot coverage and open space limits. An attached one needs 4-foot side and rear setbacks. A detached one follows the city's accessory structure setback and height rules, except that it may be up to 18 feet tall within half a mile of a major transit stop or transit corridor.

Every ADU must be at least 150 sq ft and have its own outside entrance. Only a JADU that shares a bathroom with the main home may have an inside door to it. Larger ADUs in some areas, such as Eichler (R1-e) and hillside (RHS) zones, must also meet those areas' design standards.

Two stories. The city's ADU page says a two-story ADU is allowed only when you convert existing second-story space. The 2025 code table lists a second story as allowed for a new streamlined ADU of 800 sq ft or less. HCD's handbook says a city can't deny a two-story detached ADU that fits the state height limits and the building code. Ask the Planning Division before you design a second story. [1][2][4][5]

Parking

A streamlined ADU needs no parking. If you convert or demolish a garage or other parking to build an ADU, you don't have to replace it.

For a larger ADU, the code asks for one extra off-street space only if your main home has fewer spaces than your zone requires. No space is needed if the ADU is within half a mile of a public transit stop, within one block of a car share pick-up spot, in a historic district, or part of your home or an existing accessory building. No space is needed either when the ADU's occupant isn't offered a required on-street parking permit. A junior ADU never needs parking under state law. [1][4][5]

Fees

Cupertino's code says no impact fees apply to an ADU or JADU of less than 750 sq ft. Impact fees on an ADU of 750 sq ft or more are charged in proportion to the size of the main home. The city's ADU page names these as park, storm drain and school impact fees. State law, as HCD explains it, exempts ADUs of "750 square feet of interior livable space or less." So if your ADU is exactly 750 sq ft, ask Public Works how it will be charged. HCD's handbook also says school districts may charge fees on ADUs over 500 sq ft.

For impact fee questions, call Public Works at (408) 777-3354 or the Cupertino Union School District at 408-252-3000 ext. 61-373.

You also pay building plan check and inspection fees. Plan review fees are due before plan review starts. The pre-approved plans page points to the city's Fiscal Year 2020/21 building fee schedule for ADU plan check and inspection fees, so ask the Building Division for current amounts. Ask your water provider and PG&E whether you need separate meters. Your property taxes will go up, because the County Assessor values new construction at fair market value. See our ADU cost guide. [1][2][3][5][6]

How long it takes

The Building Division's timeline table lists 10 days for the first review of a detached or attached ADU, and 10 days for each resubmittal. The same page says that, because of high volume, average plan review currently takes 20 to 30 business days for the first review and 10 to 20 business days for each later review. Plan the schedule around the longer numbers.

State law sets deadlines too. The city must tell you within 15 business days whether your application is complete. It must approve or deny a complete application within 60 days when there's already a home on the lot. Cupertino's code says ADU applications are reviewed ministerially, without discretionary review. See our ADU permit process guide. [1][3][5]

Garage conversions and junior ADUs

You can convert a garage into an ADU without replacing the parking. The city says you can't use part of a converted garage as extra living space for the main home. See our garage conversion guide.

A junior ADU (JADU) in Cupertino is up to 500 sq ft. It must be inside an existing or proposed home, made from living space, and fit within the 45% FAR limit. The city says a JADU can't be made from a garage. HCD's handbook says an attached garage counts as part of the home for a JADU, so ask the Planning Division if you want to convert an attached garage. It needs at least an efficiency kitchen. The bathroom can be shared with the main home or separate.

Cupertino's code requires that you or the owner live in either the main home or the JADU. State law has changed: HCD's handbook says owner occupancy is required only when the JADU shares a bathroom with the main home. If your JADU has its own bathroom, confirm with the Planning Division. You must record a deed restriction that bars selling the JADU separately and limits its size. The city's permit steps say to get the covenant from Planning, have it notarized and record it with the Santa Clara County Recorder before the final building inspection. [1][2][4][5][7]

Renting, selling and legalizing an ADU

You can rent out an ADU, but not for less than 30 days. The city says ADUs, including JADUs, may not be used for short-term rentals. You can't sell an ADU separately from the main home, except under the state's ADU condominium rules (Gov. Code 66340-66342). A detached ADU must have its own address; other ADUs may have one.

If you have an ADU or JADU built without permits before January 1, 2020, the code says the city can't deny a permit to legalize it just because it breaks building standards or ADU rules. It can still require fixes for conditions that are unsafe under state health and safety law. The city also won't make you fix nonconforming zoning conditions on your lot as a condition of your ADU permit. [1][2]

Lot splits (SB 9)

Cupertino's code bars any ADU or JADU on a single-family (R-1 or RHS) lot that has been split under SB 9 and has SB 9 homes approved on it. HCD's handbook says a city isn't required to allow more than two units on each lot created by an SB 9 lot split. See our SB 9 lot split guide. [1][5]

Where Cupertino and state law differ

In April 2025, the state housing agency HCD wrote to Cupertino that its 2024 ADU ordinance did not comply with state law. Among other things, HCD flagged the limit of two ADUs on a duplex lot, a 1,200 sq ft cap on detached ADUs on multifamily lots, a missing parking exemption and a design rule that wasn't objective. The city amended Chapter 19.112 later in 2025. The current code adds the eight-detached-ADU rule for multifamily lots, drops the 1,200 sq ft cap and adds a parking exemption for an ADU applied for with a new single-family home (HCD's letter also names new multifamily buildings). It still limits duplex-zoned lots to two ADUs, while HCD said a duplex lot can get up to eight detached ADUs. We found no later HCD letter on the amended code.

Other differences are the JADU owner-occupancy rule and the 750 sq ft fee line (both explained above). Where a city rule is stricter than state law, ask the Planning Division how it applies to your lot. See our California ADU law overview. [1][5][8]

Permit steps in Cupertino

1. Check the rules for your lot

   Read the city's ADU page and Development Standards. Email preliminary plans or questions to planning@cupertino.gov. [2][4]

2. Choose a design

   Hire a designer, or use a pre-approved detached ADU plan if your lot is in the Valley Floor Zone. A pre-approved application still needs a boundary survey and a site plan. [6]

3. Submit your building permit application

   Email the application, drawings and documents to permitcenter@cupertino.gov, following the city's electronic submittal format on the Building Permits page. A detached ADU also needs a new address form. [3][7]

4. Pay plan review fees and go through review

   Staff send you a payment link; plan review fees are due before review starts. Staff then send a link to start plan review. The city lists 10 days for a first ADU review, but says average first reviews currently run 20 to 30 business days. [3]

5. Pay remaining fees and get the permit

   Once your plans are approved, pay the remaining fees through the link staff send you. If the project is ready to issue, the city issues the permit shortly after payment. [3][7]

6. Build and pass inspections

   Schedule inspections online or by calling the Building Division at (408) 777-3228. For a JADU, record the deed restriction with the Santa Clara County Recorder before the final inspection. [3][7]

Pre-approved and sample plans

• Pre-Approved ADU Plans

  City-reviewed detached ADU plans from listed vendors, about 476 to 991 sq ft, for lots in the Valley Floor Zone (not fault rupture, slope instability, hillside or liquefaction areas). You still add a boundary survey and site plan. [6]

Who to call

• Planning Division

  ADU rules for your lot and preliminary review of plans (planning@cupertino.gov)

  408.777.3308

  [2][3]

• Building Permit Center

  Building permit applications, plan review and inspections (permitcenter@cupertino.gov)

  408-777-3228

  10300 Torre Avenue, Cupertino, CA 95014

  [3]

• Public Works Department

  Park, storm drain and school impact fee questions

  (408)-777-3354

  [2]

Questions people ask