Portola Valley Accessory Dwelling Unit (ADU) Standards

        New laws were recently passed, and updates will be coming soon


Arly Cassidy, Associate Planner
650.851.1700 x 230 – This email address is being protected from spambots. You need JavaScript enabled to view it.

ADU Ordinance

Zones allowed

All residential zones

Lot restrictions


Minimum lot size


Min / Max ADU size

Min: None

Max for External ADUs: 1,200 sf

Max for Internal ADUs: 1,700 sf

ADU building height

28 feet


Varies depending on zoning district and size of the parcel
Parking requirements
Internal ADUs: None
External ADUs: One parking spot is required but may be shared with primary unit on parcels 1 acre or greater. Tandem parking and parking in setbacks are allowed.
Owner occupancy

Owner must live in the main dwelling or the ADU. Short-term rentals are not allowed.

Sample fees from recently built projects*

ADU 1(800 sf, detached): $14,048
ADU 2 (500 sf, garage conversion): $8,839

Other requirements
  • Second Addresses allowed
  • ADUs must comply with all requirements of the underlying zoning district
  • Existing buildings and ADU(s) cannot exceed the total amount of allowable floor area or impervious surface for the parcel
  • If the primary dwelling has sprinklers, the ADU must have sprinklers
  • Single family lots with 3.5+ acres can have two ADUs, otherwise only one ADU is allowed
There are three review levels:
  • Ministerial Review - up to 1,000 sf that comply with certain design requirements.
  • Staff Discretionary Review - Multiple design related issues requiring discretionary review.
  • ASCC Review - Special review needed, such as historic, second driveway or non-residential zone.

Making an appointment to meet with a planner in the initial stages of the project can help avoid challenges and is highly recommended.


Some parcels under 1 acre may not qualify for ADUs based on location and fire safety requirements.

Disclaimer: standards and process may vary. Consultation with the contact is recommended before starting any project.

*Fees are specific to each project and will vary. Fees change regularly. These are provided as examples only.

Download ADU Standards PDF

Updated: 12/11/2017