Cupertino's own ADU page still says a single-family lot can hold one streamlined detached accessory dwelling unit of up to 800 square feet plus a junior unit, for a total of two. In about seven weeks, that answer will be out of date. California's AB 956 requires cities to approve two detached, newly built ADUs on a lot with a single-family home. According to a legal alert from Allen Matkins, the law takes effect January 1, 2027.
That gap matters most to anyone buying or selling a Cupertino house this winter. A buyer touring a home in November is paying for a lot whose legal capacity grows on New Year's Day. In 2024 and again in 2025, Cupertino's own permit numbers show that backyard units made up more than half of the new homes the city permitted.
Who is actually building Cupertino's new homes
The state housing department collects every California city's permit counts in its Annual Progress Report dataset, which was last updated November 6, 2026. Cupertino's building permits break down like this:
| Calendar year | ADUs permitted | Detached single-family homes permitted | All units permitted | ADU share |
|---|---|---|---|---|
| 2023 | 17 | 51 | 68 | 25% |
| 2024 | 44 | 26 | 80 | 55% |
| 2025 | 59 | 45 | 111 | 53% |
The 2024 row matches Cupertino's own 2024 progress report. That report also shows how little the better-known state shortcut produced. Six SB 9 lot-split applications came in that year, and the SB 9 streamlining path yielded zero permitted units.
For two years running, then, more than half of the new homes permitted in Cupertino have been backyard units built by individual owners, one lot at a time. Splitting a parcel requires a lot of coordination. Adding a cottage behind the house does not, and Cupertino owners have chosen the cottage. AB 956 doubles the number of detached cottages a lot can carry.
What the January rule changes on a Cupertino lot
The new state language says a city "shall ministerially approve" an application for "two detached, new construction, accessory dwelling units that do not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling." Cities keep two controls. They may cap each detached unit at "not more than 800 square feet of livable space," and they may set a height limit within the ranges the statute specifies.
Here is how the current city guidance compares with AB 956's text:
| Cupertino city guidance today | AB 956, effective January 1, 2027 | |
|---|---|---|
| Detached ADUs on a single-family lot | One streamlined unit of up to 800 sq. ft., plus a JADU | Two detached, newly built units |
| Side and rear setbacks | As close as 4 feet, for units up to 800 sq. ft. | Setbacks of no more than 4 feet |
| Size | Up to 800 sq. ft. for the streamlined unit | Each unit may be capped at 800 sq. ft. of livable space |
| HOA and deed covenants | Not addressed on the city page | Covenants that effectively prohibit or unreasonably restrict ADUs are void |
The covenant row matters most to buyers looking at planned developments and older tracts with recorded restrictions. The amended Civil Code sections make void any deed covenant or HOA governing document that "effectively prohibits or unreasonably restricts" an ADU on a qualifying single-family lot. They still allow "reasonable restrictions," which the law defines as ones that don't unreasonably raise construction costs or effectively block an otherwise lawful unit. A set of CC&Rs that once looked like a firm "no" on a backyard unit may read differently after January.
Cupertino didn't ask for this change. An October 30, 2026 legislative recap to the City Council says the city's Legislative Review Committee opposed AB 956, and the Governor signed it on September 29, 2026. The same memo says the committee also opposed AB 1751, a new law that creates a ministerial approval path for qualifying townhome subdivisions on residentially zoned land.
Why 800 square feet is Cupertino's real threshold
The state law caps each unit at 800 square feet, and Cupertino's existing rules already reward staying at or under that size. City standards exempt ADUs of 800 square feet or less from floor area ratio, lot coverage and open space limits. Larger units count against all three. Go a little smaller and the fees drop too. Per the city, ADUs under 750 square feet don't pay park or storm drain impact fees.
On a typical lot with a house already near its floor-area limit, that exemption is the reason an ADU can be built at all. Two units that each stay under 800 square feet are, in principle, outside the floor-area math that limits the main house.
The city's pre-approved plan program shows what those units look like in practice. Most of the listed designs come in well under both thresholds:
- ADORE Homes ADU: 674 sq. ft., two bedrooms, one bath
- J. Kretschmer Architect: 476 sq. ft., one bedroom, one bath
- APEX Homes USA: 495, 749 and 991 sq. ft. options
- Basically Homes, powered by Vitalize Build Construction: 499 sq. ft., one bedroom, one bath
The program has two built-in limits. It covers only detached ADUs, and it is open only to parcels in what the city calls the Valley Floor Zone. Owners can check eligibility with the Zone Lookup tool on that page. The city also says each master plan has to be updated whenever Cupertino adopts new building codes, policies or zoning updates. Any local ordinance that follows AB 956 could therefore affect these plan sets as well as the lots they're built on.
What a Cupertino lot is carrying in today's market
The Santa Clara County Association of Realtors' September 2026 report is its latest monthly table. It shows the split in Cupertino's market. In September 2026, Cupertino single-family homes recorded 18 closed sales at a median of $3,210,000, or $1,661 per square foot. They averaged 14 days on market and sold for 106% of list price, with 31 homes in inventory. Cupertino condos and townhomes had 24 units in inventory that month and one closed sale.
One month of townhome sales is too small a sample to set a price. Still, the single-family figures show where demand was strongest in September 2026: detached homes on their own lots, selling quickly and above asking. Those are the lots AB 956 applies to. A single-family buyer in Cupertino was already paying for land. Starting January 1, 2027, that land can legally hold more.
That makes some questions worth adding to a single-family purchase or listing this winter:
- Is the parcel in the Valley Floor Zone? That decides whether the faster pre-approved plan path is available.
- What do the recorded CC&Rs or HOA documents say about ADUs? After January, those clauses are judged against the state's "reasonable restrictions" standard.
- Has the garage already been converted? Under current city guidance, a garage conversion has to be the property's only ADU, and no JADU can be added alongside it.
- How much of the house's floor-area allowance is used? Units at 800 square feet or under fall outside that limit. Larger ones count against it.
Some rules hold under both the current guidance and the new law. An ADU in Cupertino can be rented but not sold separately from the main house. ADUs and JADUs can't be used as short-term rentals. A second-story ADU is allowed only when it converts existing second-floor living space. This post is general information, not legal, tax or financial advice. Confirm how these rules apply to a specific parcel with the City of Cupertino Planning Division and your own attorney or tax professional.
Quick answers
Does Cupertino's ADU page already reflect AB 956? As of this writing, the city FAQ still describes one streamlined detached ADU plus a JADU for single-family property. The state law takes effect January 1, 2027. The city's Planning Division can be reached at 408.777.3008 or [email protected].
Does building an ADU raise property taxes? Yes. The city's FAQ says the County Assessor appraises new construction, including ADUs, at fair market value, and points owners to the Santa Clara County Assessor for details.
Do I need a separate utility meter? The city directs owners to their water provider and PG&E to find out.
If you're preparing a Cupertino home for sale, or weighing an offer this winter, the team at Rob Godar & Associates can help you work out what your lot can hold under the January rules, including the zone lookup and the CC&Rs, and build that into how the home is priced and presented. Start with a free home valuation and a conversation about your parcel.
