SAN MATEO, CA

Accessory Dwelling Unit (ADU) City Regulations


Zoning:

ADU: R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D and BMSP

Junior ADU: R1-A, R1-B, R1-C, and R2

Lot Size:

N/A

ADU Floor Area:

ADU: 640 sq.ft. max

Junior ADU: 500 sq.ft. max

Note: floor area counts against total floor area allowed on a parcel. Total floor area of both ADU and primary dwelling must not exceed max. allowed for underlying zoning district.

No. of Bedrooms:

N/A

Storage / Closet:

N/A

Kitchen / Bath:  

ADU: Requires separate bathroom and kitchen facilities (permanent range, counters, refrigerator, and sink).  

Junior ADU: Requires separate “efficiency” food preparation area.

Parking:  

ADU: One off-street parking space per unit or bedroom, whichever is less. State parking exceptions apply. Parking spaces must be 10’ by 18’ without obstructions. Tandem parking allowed.

Junior ADU: No additional parking required.

Setbacks:  

ADU: must comply with underlying zoning district. No setbacks required for existing legally converted garages or other accessory structures. For ADUs constructed above a garage, a 5’ setback is required from side and rear lot lines.

Junior ADU: must comply with underlying zoning district.

Height:

Must comply with the underlying zoning district.

Location:

ADU: Must be oriented to keep windows offset from neighboring dwellings to preserve privacy. Must be designed to minimize visibility from the street, except on corner lots.

Junior ADU: By definition is located wholly within the walls of an existing dwelling, and must include the conversion of an existing bedroom.

Rear Yard Coverage:

Must adhere to requirements of underlying zoning district.

Materials / Design:  

Must have similar design elements, colors, and materials as the existing dwelling.  

Entryways:

ADU: Must have independent access from primary dwelling and cannot be closer to the street than the primary dwelling.

Junior ADU: Must have an independent entrance from primary dwelling and must have access to the common living areas of the primary dwelling which can be provided by a double lock door.

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