Bay Area region / California
Hillsborough ADU rules
& permit guide.
Planning an ADU in Hillsborough? Review local size, setback and parking requirements, then confirm the details for your property with the permitting agency.
Local source collected 2026-05-20 · View sources
Local requirements at a glance
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.
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
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
Process
Confirm your parcel and ADU type with the local planning department, prepare the required plans, and follow the city's building permit checklist. Ask which utility, fire and site reviews apply before submitting.
Your next three steps
- Confirm the property's jurisdiction, zoning and site constraints with Hillsborough's planning department.
- Discuss the ADU type, dimensions and utility needs with your designer before finalizing a layout.
- Ask the permitting agency for its current application checklist, fee estimate and review process.
2026 state-law context
ADUs and JADUs have different occupancy rules
California generally prohibits local owner-occupancy requirements for ADUs. A narrow exception applies to certain separately sold affordable ADUs. For JADUs, owner occupancy generally applies when the bathroom is shared with the main home; separate-bathroom JADUs are treated differently under 2026 law. Check the HCD handbook and your project's permit conditions.
Older local summaries may not reflect the latest state changes. Read HCD’s March 2026 handbook, pages 32–33.
Questions for your first planning conversation
- Which approval path applies to my building and ADU type?
- Do easements, trees, slope, access or fire conditions affect placement?
- Which utility upgrades and agency reviews should be included in my budget?
- Are preapproved plans available, and what site work still needs review?