Cupertino / ADU construction
ADU Construction in Cupertino
In Cupertino, 800 square feet is the number that unlocks the easy ADU.
Cupertino permitted 59 ADUs in 2025. A detached unit of 800 square feet or less skips floor area and lot coverage limits and can pair with a junior ADU; one square foot more changes the rules. We design and build ADUs here with that line, the hazard zones and the plan review queue in view.
CUPERTINO AT A GLANCE
How Cupertino handles ADUs.
Planning answers the zoning questions, the Building Division issues the permit, and much of the city sits in mapped geologic or fire hazard areas. Here is who does what.
- 59
- ADUs issued building permits in 2025, up from 44 in 2024
- 64%
- of Cupertino homes built before 1980
- 20 to 30
- business days for an initial plan review, per the city
Zoning
Planning Division
Planning offers a free preliminary review of ADU plans by email at planning@cupertino.gov, and confirms which ADU types fit the lot before the permit set is drawn.
Cupertino ADU rules ↗Permits
Building Division and Permit Center
The application goes to permitcenter@cupertino.gov, fees are paid in the Accela Citizen Access portal and plans are reviewed online. The city's target for an ADU review is 10 days, but current initial reviews average 20 to 30 business days.
(408) 777-3228Building permits ↗Hazard zones
Valley floor or hillside
Cupertino sits among active faults, and much of the city is mapped as geologic or seismic hazard area. Preapproved ADU plans are limited to the Valley Floor Zone; hillside lots need site-specific review.
Preapproved ADU plans ↗CUPERTINO ADU RULES
At or under 800 square feet, or larger?
A detached ADU of 800 square feet or less is exempt from floor area ratio, lot coverage and open space limits, can sit 4 feet from side and rear lines and can be combined with a junior ADU. Larger detached units can reach 850 square feet for one bedroom or 1,000 for two or more, but must fit the lot's floor area and coverage limits, and rule out a junior ADU.
Streamlined detached ADU
Up to 800 square feet, 4 foot side and rear setbacks, exempt from floor area, lot coverage and open space limits. Needs its own address.
Larger detached ADU
Up to 850 square feet for one bedroom or 1,000 for two or more, within the lot's floor area and coverage. No junior ADU allowed alongside.
Attached ADU
Built onto the home with no interior connection. Cannot be combined with a junior ADU on the same lot.
Junior ADU
Up to 500 square feet inside the home, not the garage, within the 45 percent floor area ratio. Owner occupancy and a recorded covenant are required.
Second stories
A two-story ADU is allowed when it converts existing second-story space. Rules have changed often, so the current code is checked for each lot.
Preapproved plans
Detached only, and only on parcels in the Valley Floor Zone, outside fault rupture, slope instability, hillside and liquefaction areas.
THE 800 SQUARE FOOT LINE
Streamlined ADU or larger ADU.
Cupertino treats a detached ADU very differently on either side of 800 square feet. The choice decides what else the lot can hold.
| Detached, 800 sq ft or less | Detached, over 800 sq ft | |
|---|---|---|
| Maximum size | 800 sq ft | 850 sq ft one bedroom, 1,000 sq ft two or more |
| Floor area and lot coverage | Exempt | Must comply |
| Side and rear setbacks | 4 ft | Per accessory structure rules |
| Junior ADU on same lot | Allowed | Not allowed |
| Park and storm drain fees | None under 750 sq ft | Apply |
Planning the work
How a Cupertino ADU gets built.
Site check
Free visit. Lot, floor area left, hazard zone, utilities and whether 800 square feet or less fits the plan.
Preliminary review
Plans emailed to the Planning Division for a free preliminary review before the permit set is finished.
Permit
Application by email, fees in Accela, plan review online. Initial reviews currently average 20 to 30 business days.
Build and final
Inspections through Accela or by phone. For a junior ADU, the covenant is recorded before the final inspection.
BEFORE YOU APPLY
What Cupertino asks for.
Documents to gather
- Construction permit application
- Full plan set to the city's electronic submittal rules
- New address form for a detached ADU
- Boundary survey and site plan for a preapproved design
- AC unit sound rating worksheet if a condenser is added
A preapproved plan fits when
- The ADU is detached
- The parcel is in the Valley Floor Zone
- It is outside fault rupture, slope and liquefaction areas
- Site concerns are cleared with city staff first
Expect a longer path when
- The lot is on a hillside or in a mapped fire hazard zone
- The ADU exceeds 800 sq ft and the lot is near its floor area limit
- A second story is planned
- Earlier additions on the lot were never permitted
WHAT SLOWS ADUS IN CUPERTINO
Problems Cupertino owners run into, and how we plan around them.
Collected from Cupertino residents' posts, local news and the city's own ADU and permit pages.
Owners find conflicting answers on two-story ADUs, setbacks and easements.
We check the lot against the current Chapter 19.112 text and confirm questions with Planning in writing before design.
Plan review is running longer than normal, by the city's own notice.
The free preliminary Planning review comes first, so the full set clears zoning on the first round.
Earlier additions by a previous owner were never permitted, and as-built drawings are needed.
Existing structures are measured at the site visit, and legalization is planned alongside the ADU permit.
Fire safety and evacuation routes have become a flashpoint for building in Cupertino's hillside areas.
The fire hazard map is checked first, and wildland-urban interface construction rules are drawn in from the start on affected lots.
A preapproved plan turns out not to qualify because of a hazard zone.
The parcel is checked in the city's lookup before any plan is chosen; only Valley Floor Zone lots use preapproved designs.
Sources: r/Cupertino threads, 2025 to 2026; cupertino.gov ADU, preapproved plan and permit pages.
How big can an ADU be in Cupertino?
800 square feet for a streamlined detached ADU exempt from floor area and lot coverage limits, or up to 850 square feet for one bedroom and 1,000 square feet for two or more if the lot's floor area allows. A junior ADU is capped at 500 square feet, and detached ADUs on multifamily lots can reach 1,200.
How many ADUs can I build on a single-family lot in Cupertino?
Two at most: a junior ADU plus one detached ADU of 800 square feet or less. A junior ADU cannot be combined with an attached ADU or with a detached ADU larger than 800 square feet, so a bigger unit means one ADU only.
Can I build a two-story ADU in Cupertino?
Yes, when it converts existing second-story space in the home, according to the city's ADU information sheet. A new detached ADU is generally single-story, so height limits for the specific lot are confirmed with the Planning Division before design.
Are there impact fees for an ADU in Cupertino?
No park or storm drain fees for an ADU under 750 square feet. Larger ADUs pay impact fees, and ADUs of any size may owe school fees to the Cupertino Union and Fremont Union High school districts. Public Works answers fee questions at (408) 777-3354.
Can I use a preapproved ADU plan anywhere in Cupertino?
No. Cupertino limits preapproved ADU plans to detached units on parcels in the Valley Floor Zone, outside fault rupture, slope instability, hillside and liquefaction areas. The city's online lookup shows whether a parcel qualifies.
Can I sell or rent out an ADU in Cupertino?
Rent yes, sell no. Cupertino allows ADUs to be rented but not sold separately from the main home, and bans short-term rentals of ADUs and junior ADUs. For a junior ADU, the owner must live in the main home or the junior unit.
