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Local ADU Rules

Foster City

Last Updated August 29, 2024

ADU Contact:

Building@fostercity.org or Planning@fostercity.org

Standards	Details
Zones allowed	R-1, R-2, R-3, R-4, R-T, PD that allow for single-family and multifamily residences
Lot Restrictions	Attached and Detached ADUs not permitted in front yard
Minimum Lot Size	None
Min/Max ADU Size	Min:150 square feet Max ADU in single-family zoning districts: 1200 square feet or 50% of main home floor area (whichever is less), unless under 800 square feet (state law allows an ADU up to 800 square feet on every property, some exceptions may apply) Max ADU in multi-family zoning districts: 850 square feet for one bedroom, 1000 square for two or more bedrooms Max JADU: 500 square feet
ADU Building Height	JADU – Within existing structure Attached ADU: Shall not exceed 25 feet in height, or the height of the primary dwelling, whichever is lower. ADUs shall not exceed two stories in height. Detached ADU: 16 feet, except within ½ mile of major transit stop or high-quality transit corridor – 18 feet; 2 feet may be added to align with roof pitch of primary dwelling; 18 feet maximum for multi-family, multi-story ADU
Setbacks	Side and Rear: 4 feet Front: may not be located in the front yard.
Parking Requirements	JADUs: No parking required ADUs: One spot may be required (tandem allowed). No parking required if: The ADU is located within one-half mile walking distance of public transit. The ADU is a conversion ADU. When there is an approved car share vehicle for which a Foster City business license has been issued and remains active, located within one block of the accessory dwelling unit. ADU that only includes a studio with no bedroom.
Owner Occupancy	JADU: Required, ADU: not required for ADUs built recently (2020-2024)
Sample fees from recent permits	Fees are based off of the job valuation. Contact Foster City Building Division by emailing building@fostercity.org Attached ADU – 2020, 980 sq. ft., $198k, $8032.66 BP Fee Detached ADU – 2021, 564 sq. ft., $200k, $7,600.71 BP Fee JADU – 2021, 256 sq. ft., $64k, $4649.83 BP Fee
Other requirements	Shall comply with the California Building Code JADUs and ADUs shall provide exterior access separate from primary dwelling unit An ADU shall not be required to provide fire sprinklers if they are not required for the primary residence and may employ alternative methods for fire protection. Short term rentals are not allowed ADU must be clearly subordinate to primary dwelling by size, location, and appearance. Sale of JADU separate from the primary dwelling is prohibited (deed restriction required) Number of ADUs: 1 JADU; One ADU (attached or detached); or One new constructed detached ADU and one JADU
Process	ADUs are subject to a Building Permit. Making an appointment to meet with a planner and the Building Official in the initial stages of the project can help avoid challenges and is highly recommended.
Exceptions	None

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