Hillsborough - San Mateo County ADU Resource Center

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Local ADU Rules

Hillsborough

Last Updated January 5, 2025

ADU Contact:

Planning Division – 650.375.7422

Standards	Details
Zones allowed	All residential areas
Lot Restrictions	Floor area ratio & lot coverage requirements for underlying zone apply, unless these would preclude the construction of an ADU that is 800 square feet.
Minimum Lot Size	None
Min/Max ADU Size	JADU: 500 sq. ft. Building Permit Only: 800 sq. ft. Detached/Attached ADU Planning Permit (one bedroom or less): 850 sq. ft. Detached/Attached ADU Planning Permit (2+ bedrooms): 1,000 sq. ft. Applicant can request an ADU Exception Review, which allows more permissive standards through a discretionary review process.
ADU Building Height	Detached: Up to 16 feet. If site is within ½ mile walking of transit, then 18 feet is allowed (Up to 20 feet if necessary to accommodate a roof pitch). Detached with increased setbacks: Up to 22 feet, if ADU has side and rear setbacks of at least 20 feet and is at least 25 feet from all public right-of-way. Attached: Up to height of primary dwelling or 25 feet, whichever is lower.
Setbacks	Side and Rear: 4 feet Front: 25 feet, unless these would preclude the construction of an ADU that is 800 square feet No setback is required for an ADU that is constructed in the same location and to the same dimensions as an existing structure
Parking Requirements	JADUs: No parking required ADUs: One spot may be required (tandem or within setback allowed). No parking required if: ½ mile walking distance from public transit, in a historic district, or one block from a car-share vehicle, or on-street parking permits are required but not offered to ADU occupant when the ADU application is submitted with an application to create a new primary dwelling
Owner Occupancy	JADU: Required ADU: Not required for ADUs created on or after January 1, 2020
Sample fees from recent permits	ADU 1 (2019, 674 sf, detached): $4,800 ADU 2 (2019, 437 sf, detached): $3,400 No impact fees if ADU is under 750 square feet
Other requirements	ADUs must comply with Building and Fire Code requirements. No short-term rentals (less than 30-days). ADU Planning permits subject to all objective standards, including Architecture and Landscaping Requirements. Additional requirements may apply if: the site is within a HFSZ or WUI Zone the structure is or lot contains a historic resource the ADU or necessary site work is within 20 feet of the top of bank of a creek
Process	Please contact our ADU Specialist via email at adu@hillsborough.net, or make an appointment here (https://outlook.office365.com/book/VirtualADUSpecialistBooking@hillsborough.net/s/ ZOlGkmYc7UmoPbxPIIwf5w2).
Exceptions	Applicant can request an ADU Exception Review, which allows more permissive standards through a discretionary review process. An ADU or JADU that does not comply with every applicable objective standard may be approved through a staff-level the design review.

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