San Mateo Municipal Code Ch. 27.19 Accessory Dwelling Unit and Junior Accessory Dwelling Unit—residential…

Prior ordinance history: Ord. Nos. 1983-16, 1989-18, 1991-12, 1997-20 and 2003-12.

Article I Accessory Dwelling Unit

The purpose of this Article is to set forth regulations to permit accessory dwelling units on residential zoned properties (R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D and BMSP) with a single-family residential use. A parcel with a single-family residential use, may have only one accessory dwelling unit (ADU) or one junior accessory dwelling unit (JADU), but not both.

Properties with approved accessory dwelling units may not be subdivided at the time the units are approved or thereafter.

(a) An accessory dwelling unit shall not be sold separately from the primary residence.

(b) If an accessory dwelling unit is rented, the unit shall not be rented for a period of less than 30 consecutive calendar days.

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 Article. If the accessory dwelling unit is in full compliance with the provisions of this Article, a ministerial, non-discretionary permit will be issued.

An accessory dwelling unit, as defined in Section 27.04.165, shall comply with the following development standards:

(a) Permitted Zoning Districts. Accessory dwelling units shall only be constructed on residential zoned properties, specifically R1-A, R1-B, R1-C, R2, R3, R4, R5, R4D, R5D, R6D and BMSP, that have been developed with a single-family dwelling unit or an accessory dwelling unit is proposed to be built in conjunction with a single-family dwelling unit, where the single-family dwelling is the primary residential dwelling unit. The residential property shall not be part of a condominium, townhouse, or other multi-family development.

(b) 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.

(c) Owner Occupancy. One of the dwelling units on the site shall be owner-occupied.

(d) Maximum Unit Size. The floor area of an accessory dwelling unit shall not exceed 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.

(e) 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, unless otherwise provided in this Article.

(f) Maximum Coverage of Rear Yard. Accessory buildings shall not occupy more than 50% of a required rear yard.

(g) Existing Accessory Structure. When any accessory dwelling unit is proposed to be attached to an existing accessory structure, the entire structure must comply with all standards for the principal use of the subject site and underlying zoning district, and not those standards for an accessory structure.

(h) Separate Entry, Cooking Facility/Kitchen and Bathroom. The accessory dwelling unit, attached or detached, shall contain a separate entrance, cooking facility/kitchen, and bathroom.

(i) Wetbar. One wetbar is permitted in a dwelling unit in a common living area room only. A single half-size or small refrigerator is permitted, but a microwave is not.

(j) Location of Accessory Dwelling Unit. The accessory dwelling unit may be within, attached to, or detached from the primary dwelling unit.

(1) Setback Exceptions.

a. No setback shall be required for an existing legally permitted garage or accessory structure that is converted to an accessory dwelling unit.

b. A minimum setback of five 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.

(k) Number and Type of Required Parking.

(1) General Requirements. There shall be a minimum of one standard size off-street parking space for an accessory dwelling unit with up to one bedroom and one 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.

(2) Location of Required Parking for Accessory Dwelling Unit. The required parking for the accessory dwelling unit may be located on the rear one-third 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 of the property.

(3) 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.

a. 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.

b. Landscape and Limits on Paving Standards. The required replacement parking located on the subject property shall be designed to comply with the landscape and paving standards set forth in Section 27.18.070(d) and 27.18.080(b)(4), "Limits on paving" standards.

(4) All required parking spaces shall be a minimum of 10 feet wide by 18 feet long without any obstructions.

(5) Parking Exemptions. No additional parking shall be required for an accessory dwelling unit in the following instances:

a. The accessory dwelling unit is located within one-half mile of public transit stop;

b. The accessory dwelling unit is located within an architecturally and historically significant historic district;

c. The accessory dwelling unit is in part of the existing legally permitted primary residence or an existing legally permitted accessory structure;

d. In an area requiring on-street parking, permits are required but not offered to the occupant of the accessory dwelling unit.

(l) Architectural Standards. New accessory dwelling units and conversions of an existing legally permitted structure shall be designed to comply with the following standards:

(1) Attached Accessory Dwelling Units. Accessory dwelling units that are attached to the primary residential dwelling unit shall:

a. Locate the primary entrance to the accessory dwelling unit no closer to the street than the primary residential dwelling unit;

b. Be of the same architectural style as the primary structure;

c. Be constructed of the similar exterior materials, finishes, and family of colors as the primary residential dwelling unit; and

d. Offset windows from neighbor's windows to maximize privacy.

(2) Detached Accessory Dwelling Units. Accessory dwelling units that are detached from the primary residential dwelling unit shall:

a. Comply with the architectural standards listed above under attached accessory dwelling units;

b. Be designed to minimize the visibility of the accessory dwelling unit from the street(s), with the exception that corner lots are excluded from this requirement; and

c. Offset windows from neighbor's windows to maximize privacy.

(m) Heritage Tree Standards. New accessory dwelling units and conversions of an existing legally permitted structure shall be designed to comply with the standards for the preservation of heritage trees in Chapter 13.52, "Heritage Trees."

(n) 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.

(o) 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.

(p) Other Requirements. All other zoning requirements shall be complied with unless an authorized variance is approved.

(a) 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:

(1) Only one unit may be occupied solely by persons other than the owner or owners of record.

(2) If an accessory dwelling unit is rented, the unit shall not be rented for a period of less than 30 consecutive calendar days.

(3) Sale of the accessory dwelling unit separately from the sale of the single-family residence is prohibited.

(4) The approved size and attributes of the accessory dwelling unit.

(b) A copy of this deed restriction must be given to each prospective occupant.

Article II Junior Accessory Dwelling Unit

The purpose of this Article is to set forth regulations to permit junior accessory dwelling units on one- and two-family residential zoned properties (R1-A, R1-B, R1-C, and R2). A parcel with an existing legally permitted single-family use may have only one accessory dwelling unit or one junior accessory dwelling unit, but, not both.

Properties with approved junior accessory dwelling units may not be subdivided at the time said unit is approved or thereafter.

(a) A junior accessory dwelling unit shall not be sold separately from the primary residence.

(b) If a junior accessory dwelling unit is rented, the unit shall not be rented for a period of less than 30 consecutive calendar days.

A junior accessory dwelling unit permit application is required in order to demonstrate that the unit is in compliance with the provisions of this Article. If the junior accessory dwelling unit is in full compliance with the provisions of this Article, a ministerial, non-discretionary permit shall be issued.

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

(a) Permitted Zoning Districts. Junior accessory dwelling units shall only be constructed on one- and two-family residential zoned properties, specifically R1-A, R1-B, R1-C, and R2, with an existing legally permitted single-family dwelling. The residential property 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 junior accessory dwelling units is limited to one per residential parcel zoned for one-family dwelling unit or two-family dwelling units with a single-family dwelling already built on the parcel.

(c) Setback and Other Zoning Regulations. For purposes of setbacks and other zoning regulations, the junior accessory dwelling unit 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 junior accessory dwelling unit shall not exceed 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.

(e) Construct within Existing Structure. The junior accessory dwelling unit shall be constructed within the existing walls of an existing, legally permitted single-family dwelling unit and must include the conversion of an existing, legally permitted bedroom.

(f) Unit Access.

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

(2) An interior entry access between the junior accessory dwelling unit and the one-family dwelling that is located off of the common living area of the primary residence, such as the living room, family room, dining room, den, office, home gym, kitchen, or an interior hallway leading to these common living areas. This interior entry access may be a door equipped with a double lock. A permitted junior accessory dwelling unit may include a second interior door for sound attenuation.

(g) Efficiency Food Preparation Area. A junior accessory dwelling unit shall include a small efficiency food preparation area that is limited to the following components:

(1) A sink with a maximum width and length dimensions of 16 inches and with a maximum waste line diameter of one and one-half inches;

(2) Food preparation appliances that do not require electrical service greater than 120 volts or natural or propane gas;

(3) A food preparation counter and storage cabinets which do not exceed six feet in total length.

(h) Wetbar. One wetbar is permitted in a dwelling unit in a common living area room only. A single half-size or smaller refrigerator is permitted, but a microwave is not.

(i) Building and Fire Requirements.

(1) No fire wall separation or noise attenuation measures are required between the main 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" as defined by Chapter 23, Building and Construction, of the San Mateo Municipal Code. 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.

(2) The junior accessory dwelling unit 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 junior accessory dwelling unit.

(k) Parking. No additional off-street parking is required for a junior accessory dwelling unit.

(a) 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:

(1) Only one unit may be occupied solely by persons other than the owner or owners of record.

(2) If a junior accessory dwelling unit is rented, the unit shall not be rented for a period of less than 30 consecutive calendar days.

(3) Sale of the junior accessory dwelling unit separately from the single-family residence is prohibited.

(4) The approved size and attributes of the junior accessory dwelling unit.

(b) A copy of this deed restriction must be given to each prospective occupant.