Portola Valley Second Units

Portola Valley has produced a Second Units Handout


To have an ADU on your property in Portola Valley, your parcel must be at least one acre in size, have a main house on it, and be located in a residential zoning district.

ADUs count towards the property’s overall allowable floor area and impervious surface. You will be responsible for ensuring the existing buildings and potential ADU do not exceed the total amount of allowable floor area or impervious surface for your parcel.

Maximum Floor Area

Parcel Size 1 – 1.99 acres, ADU can be up to 1,000 sq.ft.

Parcel Size 2 – 3.49 acres, ADU can be up to 1,200 sq.ft.

Parcel Size over 3.5 acres, one ADU can be up to 1,500 sq ft. or two can be built no more than 1,000 sq.ft. each


  • 1 space for studio or 1 bedroom; 2 spaces for 2+ bedrooms
  • Parking for ADUs must be provided in addition to the amount of parking needed for the main house.
  • Required parking spaces for the ADU do not have to be covered and can be provided as tandem spaces (behind other required parking, such as in a driveway).
  • No additional parking space is required if the ADU is created by conversion of existing space within the main dwelling unit.

Light Reflectivity Value:

  • Main body finish – 40% or less
  • Trims – 50% or less
  • Roof – 50% or less


  • The ADU shall have the same address as the main dwelling.
  • ADUs may not be sold separately from the main dwelling.
  • Either the ADU or the main dwelling shall be owner occupied. If the ADU is rented, any such rental shall not be for a term of less than 30 days.

For the full Ordinance, see Ordinance 2017-420

Portola Valley website