Atherton - San Mateo County ADU Resource Center

Home » Local Rules » Atherton

Local ADU Rules

Atherton

Last Updated October 1, 2024

ADU Contact:

Brittany Bendix: bbendix@ci.atherton.ca.us – 408.688.2432

Standards	Details
Zones allowed	All residential zones (R-1A and R-1B)
Lot Restrictions	None
Minimum Lot Size	None
Min/Max ADU Size	Detached and Attached: 1200 square feet if setback requirements met Attached: less than 50% of primary dwelling, no more than 1200 feet JADU: 500 square feet
ADU Building Height	Attached: height of main dwelling Detached: 16-18 feet
Setbacks	Attached: <800 sqft ADUs: Up to 4 feet. Same as primary dwelling in R-1A and R-1B. >800 sqft ADUs: Can encroach 20% into the required side and rear setbacks. Detached: ADUs 800-1,200 sqft: 120 feet from front property line or 30 feet behind front line of the main residence, whichever is less. 10 feet side yard and rear. ADUs <800 sqft: 4 foot side and rear setback.
Parking Requirements	JADUs: No parking required ADUs: One spot may be required (tandem allowed). No parking required if: a. ADU is located within one-half mile of public transit. b. ADU is part of a proposed or existing primary residence or an existing accessory structure. c. On-street parking permits are required but not offered to the occupant of the ADU. d. A car share vehicle is located within one block of the ADU.
Owner Occupancy	1. ADUs and JADUs Permitted Before January 1, 2020. The owner-occupancy requirements applicable to the ADU or JADU at the time of its permitting shall apply. 2. ADUs and JADUs Permitted Between January 1, 2020, and January 1, 2025. No owner-occupancy requirements shall apply. 3. ADUs and JADUs Permitted After January 1, 2025. Prior to finaling of the project for an ADU or JADU, the property owner shall record a deed restriction requiring that the owner of the property occupy either the primary dwelling unit, ADU, or JADU, or, if the owner will not be residing in one of the units, lease the entire property including the primary dwelling unit, ADU, and JADU to a single tenant.
Sample fees from recent permits	Detached ADU, 1,199 square feet, $515,550 valuation: Planning: $1,380.41; Building Dept Permit fees: $5,601.62
Other requirements	One JADU and two ADUs per parcel No short term rentals
Process	Making an appointment to meet with a planner in the initial stages of the project can help avoid challenges and is highly recommended. For construction of new units, Staff will review for compliance with physical standards within 60 days. Process can be found here: Plans & Specifications / Submittal Requirements (atherton.ca.us)
Exceptions	ADUs 800-1200sqft exempt from FAR based on setbacks

Wondering what you can build?

Make sure you check out our Learning the Rules page for more step-by-step details