Global Announcement Text

Portola Valley, California: ADU Regulations

City or County:

Portola Valley, California

Date Updated:




Types of ADUs:

External, Attached, Internal and Garage Conversion


Up to 2 stories allowed.

Lot Size:

Min. 1 acre

Maximum ADU Floor Area:

AMFA applies

Max 1,700 sq. ft.

External ADU maximum of 70% of main building

Max size is smallest of three numbers (unbuilt AMFA / 1,700 sq. ft. / 70%)

Note: ADU basement counts toward ADU size, but not AMFA

Lot Coverage:



No min/max


No min/max


ADUs must have separate kitchen facilities.


ADUs require a full bathroom.

Note: Drainage and sewer connections should be assessed on a project by project basis.


No parking required for internal ADU. 1 parking space required for external ADU. On 1 acre or more, ADUs < 1,200 sq. ft. can overlap guest & ADU parking. Separate driveway permitted rarely. Spaces do not have to be covered and can be in tandem. No additional parking space is required if the ADU is created by conversion of existing space within main dwelling.


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 the 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.

Note: Fire Department regulations should be assessed on a project by project basis.


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 residential design 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.

Note: Historic Neighborhoods or Districts should be assessed on a project by project basis.



Source Code:

Important Note: Rules and regulations are updated and changed frequently. It’s one of our jobs to be up to speed and navigate those regulations. Let us know if our website isn’t up to date or if you have any information that could help. Cheers!