Hillsborough Accessory Dwelling Unit (ADU) Standards

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


Planning Department – 650.375.7422

ADU Ordinance

Zones allowed

All residential areas
Lot restrictions


Minimum lot size


Min / Max ADU size

None / 1400 sf

ADU building height

32 feet, 22 foot wall height (same as primary residence)


Same as primary residence – minimum 25’ from front property line and 20’ from side property lines. Conversion of a legally nonconforming structure within the required setbacks is permitted however.

Parking requirements
For 1-2 bedroom units, one unenclosed space is required and for 3+ bedroom units, two unenclosed spaces are 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). Tandem parking and parking in setbacks is allowed.
Owner occupancy

No requirement

Sample fees from recently built projects*
ADU 1 (674 sf, detached): $4,847
ADU 2 (437 sf, detached): $3,445
Other requirements
  • ADUs must comply with Building and Fire Code requirements.
  • Design must be consistent with primary residence and neighborhood.
  • Removal of trees over 36” in diameter (at breast height) or groves of any size trees requires a permit for removal.
  • Additional requirements may apply if structure is a historic resource and/or if ADU is within 20 feet of a creek.
  • Only one ADU per property is allowed.
  • ADUs must comply with all requirements of the underlying zoning district.

ADUs require administrative review without public notification, hearing, or fee. Design review is also required to ensure architectural consistency. Making an appointment to meet with a planner in the initial stages of the project can help avoid challenges and is highly recommended.



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