Cupertino refers to ADUs both as Accessory Dwelling Units, Secondary Dwelling Units and Granny Units.

Cupertino Development Standards:

You may build an Accessory Dwelling Unit if you are located in R1, RHS, A and A-1 Zoning districts.

Minimum Size Maximum Size
Size of Accessory Dwelling Units 150 s.f. 10% of the net lot area, up to a maximum of 1,000 s.f., or 50 percent of the existing living space of the principal dwelling unit, whichever is more restrictive.

This separate residential unit may be detached if the lot is greater than 10,000 s.f. but should be attached if the lot is smaller than 10,000 s.f. It may be detached on lots less than 10,000 s.f., if the proposed architecture, colors, materials etc are consistent with the main house.

An accessory dwelling unit:

  • Must have direct outside access without going through the principal dwelling
    • May have secondary access through the principal dwelling
  • Entrance must be screened from a public street
  • May be located on the second story if:
    • It is conversion of a portion or all of an existing second story
    • It is attached to the main house
    • Entry is not through an exterior/exposed staircase
    • Does not result in privacy intrusion to adjoining dwellings (must provide privacy planting)

for more, see The City of Cupertino Guidelines