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Portola Valley CA ADU Guidelines

Accessory Dwelling Unit (ADU) City Regulations


Attached/Detached: R1/RE

Lot Size:

Min. 1 Acre

Maximum ADU Floor Area:

Lot Size                   Max Floor Area

1 to 1.99 acres            1,000 sq.ft.
2 to 3.49 acres            1,200 sq.ft.
>3.5 acres                     One 1,500 sq.ft. unit or two 1,000 sq.ft. units

No. of Bedrooms:    

No min/max


No min/max


Must have separate kitchen and full bathroom.


1 space for studio or 1 bedroom; 2 spaces for 2+ bedroom must be provided in addition to parking required for main dwelling, tandem parking permitted; ADU spaces do not have to be covered. No additional spaces required if ADU created by conversion of existing space within main dwelling. Second unit and main dwelling must be served by same vehicular access to main street.


Front, side and rear yard setbacks vary depending on both parcel size and combining district. Refer to Table 1 in Section 18.48.010 of municipal code.

No setback required for existing garage conversion and setback of no more than 5' from side and rear lot lines required for ADU constructed above garage.


Max: 18' to 24'. However, with ASCC approval, can be up to 34'.


Cannot be visible from a local scenic corridor without ASCC approval.

Rear Yard Coverage:



Must comply with site development and design standards of applicable district, additionally, all ADU projects must meet the 2013 Cal Green Code requirements. Colors, materials, and architecture must match main dwelling unless approved by ASCC.

ADU applications submitted to Town Planner must be reviewed by Town Geologist, Director of Public Works, Fire Chief, and County Health Department.



For more ADU Information:

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