Foster City Accessory Dwelling Unit (ADU) Standards

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


Timothy Maier, Associate Planner


ADU Ordinance

Zones allowed

R-1, R-1/PD, R-2

Lot restrictions

Must be single-family dwelling

Minimum lot size 5,000 sf
Min / Max ADU size

150 sf / 640 sf

ADU building height 25 feet (for an attached ADU placed at the second story of a single-family home); for all other ADU configurations, consult City Planning staff


ADU is subject to the same setbacks as primary dwelling (typically 20 feet front, 5 feet side and 20 feet rear). There is a minimum 10-foot setback between a detached ADU and the primary dwelling.

Parking requirements

One parking space is required unless state exemptions are met (ADU is within 1⁄2 mile of transit, in existing structures, or within one block of car share locations). Parking can be uncovered and in tandem with covered parking. Tandem parking and parking in setbacks are allowed (assuming no public safety concerns).

Owner occupancy

Owner must live in the main dwelling or the ADU

Sample fees from recently built projects*

ADU (430 sf, attached): $12,094

Other requirements
  • Fire sprinklers are required, unless the ADU is built within the existing primary residence and not otherwise required.
  • ADU must be clearly subordinate to primary dwelling by size, location, and appearance.
  • Provisions of Municipal Code and City’s Architectural and Solar Guidelines apply.
  • Utility connections as required by Utilities and/or Building and/or other Code.
  • ADU is subject to solar impact requirements applicable to primary residences or room additions.
  • Owner-occupancy deed restriction is required.
  • ADUs must comply with all requirements of the underlying zoning district.
  • Only one ADU per property is allowed.

ADUs are subject to Architectural Review (design review), which requires that staff make specific findings for any residential additional project. A Planning Commission hearing is required for waterfront additions of 200+ square feet or second-story additions of 400+ square feet. 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