Atherton Accessory Dwelling Unit (ADU) Standards

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


Lisa Costa Sanders - This email address is being protected from spambots. You need JavaScript enabled to view it., 650.572.0544

ADU Ordinance

Zones allowed

All residential zones (R-1A and R-1B)

Lot restrictions


Minimum lot size

R-1A: 1 acre

R-1B: 12,520 sf

Min / Max ADU size

None / 1,200 sf

ADU building height

Attached: 32 feet

Detached:15 feet


Attached: same as primary dwelling (60 feet front, 50 feet rear and sides)

Detached: 48 feet front, 40 feet rear and sides

(applies to typical 1 acre lots)

Parking requirements
One parking space per unit is required unless state exemptions are met (ADU is within 1⁄2 mile of transit, in existing structures, in historic districts, within one block of car share locations, or in an area with residential parking permit rules that do not allow second units to get a permit). Parking is allowed in setbacks. Tandem parking is not allowed.
Owner occupancy

Owner must live in the main dwelling or the ADU

Sample fees from recently built projects* n/a
Other requirements
  • Only one ADU per property is allowed

Staff will review for compliance with physical standards. Making an appointment to meet with a planner in the initial stages of the project can help avoid challenges and is highly recommended.


Extra square footage is allowed in the main dwelling if an ADU is included.

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

Download ADU Standards PDF

Updated: 12/11/2017