The city government of San Mateo has updated its local zoning codes to comply with the State ADU mandate.
Number of ADUs allowed:
Number of Units. No more than one accessory dwelling unit may be constructed on any site. An accessory dwelling unit shall not be allowed on a site with more than one unit.
Types of ADUs allowed:
Attached, Detached or junior ADU. Conversion of existing space or new construction permitted.
Minimum lot size is determined by the maximum density of the underlying zone.
The floor area of an accessory dwelling unit shall not exceed six hundred and forty (640) square feet including attic and basement areas as defined in Section 27.04.200 for the applicable underlying zoning district, provided that the total floor area for the parcel or lot does not exceed the maximum allowable floor area. The floor area of a junior accessory dwelling unit shall not exceed five hundred (500) square feet, including attic and basement areas as defined in Section 27.04.200 for the applicable zoning district, provided that the total floor area for the parcel or lot does not exceed the maximum allowable floor area.
Setback and Other Zoning Regulations. For purposes of setbacks and other zoning regulations, the accessory dwelling unit (both attached and detached) 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, including standards for lot coverage, setbacks, and height. No setback shall be required for an existing legally permitted garage or accessory structure that is converted to an accessory dwelling unit. A minimum setback of five (5) feet shall be required from the side and rear lot lines for an accessory dwelling unit that is constructed above an existing legally permitted garage.
General Requirements. There shall be a minimum of one (1) standard size off street parking space for an accessory dwelling unit with up to one (1) bedroom and one (1) standard size parking space shall be required for each additional bedroom. The required accessory dwelling unit parking may be located in a garage, carport, uncovered or tandem space. In addition, the required parking for the primary residential dwelling unit must comply with current code standards, as specified by the underlying zoning district. Exemptions: The accessory dwelling unit is located within one-half (1/2) mile of public transit stop. The accessory dwelling unit is located within an architecturally and historically significant historic district. The accessory dwelling unit is in part of the existing legally permitted primary dwelling or an existing legally permitted accessory structure. In an area requiring on-street parking, permits are required but not offered to the occupant of the accessory dwelling unit.
Location of Required Parking for accessory dwelling unit. The required parking for the accessory dwelling unit may be located on the rear one-third (1/3) of the property, including the required rear yard setback and a portion of the required side yard and street side yard setback areas. The required parking shall not be located within the required front, interior side yard, or street side yard setback areas outside of the rear one-third (1/3) of the property. Replacement Parking for primary dwelling. When a garage, carport, or covered parking structure is demolished or converted in conjunction with the construction of an accessory dwelling unit, and the required off-street parking spaces for the primary single-family dwelling unit must be replaced, the replacement spaces shall be located on the same parcel as the accessory dwelling unit in the following configurations, or a combination thereof: garage parking spaces, carport parking spaces, uncovered parking spaces, or tandem parking spaces.
The required replacement parking may be located within the required front yard setback, street SIDE setback, and rear yard setback areas. It may also be located within a portion of the interior side yard setback provided that minimum five-foot wide side yard clearance with no obstruction is maintained.
No fire wall separation or noise attenuation measures are required between the primary dwelling and the junior accessory dwelling unit. No fire sprinklers are required for the junior accessory dwelling unit, unless the associated improvements meet the threshold for a "substantial remodel". The junior accessory dwelling unit shall have an adjoining door connected to the main LIVING area for fire separation. A smoke alarm shall be required in the junior accessory dwelling unit and shall be connected to the smoke alarm in the main residence. Fire sprinklers are not required for the ADU unless they are required for the primary dwelling.
Shape, materials and style:
Architectural Standards. New accessory dwelling units and conversions of an existing legally permitted structure shall be designed to comply with the following standards: be constructed of the similar exterior materials, finishes, and family of colors as the primary residential dwelling unit; and be designed to minimize the visibility of the accessory dwelling unit from the street(s), with the exception that comer lots are excluded from this requirement. Require that the design of ADUs be compatible with the main residence and neighborhood, provide adequate on-site usable open space and parking, and not infringe upon the privacy of adjoining properties
Height of the ADU is determined by the underlying zone.
An accessory dwelling unit permit application for either an attached or a detached accessory dwelling unit is required in order to demonstrate that a unit is in compliance with the provisions of this Chapter. If the accessory dwelling unit is in full compliance with the provisions of this Chapter, a ministerial, non-discretionary permit will be issued. A junior accessory dwelling unit permit application is required in order to demonstrate that the unit is in compliance with the provisions of this section. If the junior accessory dwelling unit is in full compliance with the provisions of this section, a ministerial, non-discretionary permit shall be issued.
Number of Bedrooms:
Not specified by State Standards.
Prohibition on Sale and Limitation on Rental. Owner Occupancy: One of the dwelling units on the site shall be owner occupied. A deed restriction shall be recorded to run with the land and submitted to the City prior to building permit issuance, which indicates the following: Only one unit may be occupied solely by persons other than the owner or owners of record.
Utility Service. A separate water connection, a separate sewer service connection, and power connection as water, sewer, and power service is not required for an accessory dwelling unit. Utility Fees. accessory dwelling units shall not be considered new residential uses for the purposes of calculating city connection fees or capacity charges for utilities, including water and sewer service. For an accessory dwelling unit located within an existing structure, neither the installation of a new or separate utility connection nor the payment of a connection fee or capacity charge is required. For an accessory dwelling unit that is separate from an existing structure, the city will require a new or separate utility connection directly between the accessory dwelling and the utility detector.
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 junior accessory dwelling unit.
ADU Manual / Guide