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City of San Mateo Municipal Code.

27.19.110 Development Standards.

A "junior accessory dwelling unit," as defined in Section 27.04.165, must comply with the following development standards:

(a) Permitted Zoning Districts. JADUs shall only be constructed on lots zoned to allow single-family residential use, or for which a single-family residence exists or is proposed to be built. The residential lot shall not be part of a condominium, townhouse, or other multi-family development.

(b) Limit to the Number of Junior Accessory Dwelling Units. The number of JADUs is limited to one per residential lot with a single-family residence. Lots with multi-family housing or more than one detached single-family dwelling are not eligible for JADUs.

(c) Setback and Other Zoning Regulations. For purposes of setbacks and other zoning regulations, the JADU shall be considered to be a part of the principal use of subject site and shall be subject to the same requirements of the underlying zoning district.

(d) Maximum Unit Size. The floor area of a JADU shall not exceed 650 square feet, including attic and basement areas as defined in Section 27.04.200 for the applicable zoning district.

(e) Construct within Existing Structure. The JADU shall be constructed within the walls of the proposed or legally existing single-family dwelling unit, including an attached garage. Detached accessory structures, including detached garages or carports, are not permitted to be converted into JADUs.

(f) Unit Access. A JADU must include:

(1) A separate exterior entry from the main entrance to the single-family dwelling, which shall be provided to serve the JADU only; and

(2) An interior entry access between the JADU and the single-family dwelling. This interior entry access may be a door equipped with a double lock. A permitted JADU may include a second interior door for sound attenuation.

(g) Efficiency Food Preparation Area. A JADU shall include an efficiency kitchen that includes the following components:

(1) Cooking facility with appliances; and

(2) Food preparation counter and storage with cabinets that are of reasonable size in relation to the size of the JADU.

(h) Sanitation Facilities. A JADU may include its own separate sanitation facilities or may share sanitation facilities with the primary dwelling unit.

(i) Building and Fire Requirements.

(1) No fire wall separation or noise attenuation measures are required between the main dwelling and the JADU. No fire sprinklers are required for the JADU, unless the associated improvements meet the threshold for a "substantial remodel" as defined by Chapter 23, Building and Construction, of the San Mateo Municipal Code. The JADU shall have an adjoining door connected to the main living area for fire separation. A smoke alarm shall be required in the JADU and shall be connected to the smoke alarm in the main residence.

(2) The JADU shall be equipped with a carbon monoxide detector.

(j) Utility Service. A separate water connection, a separate sewer service connection, and power connection as water, sewer, and power service is not required for a JADU.

(k) Parking. No additional off-street parking is required for a JADU.

(l) Address Assignment. An application for a building permit for a JADU must include application for a separate address assignment.