Half Moon Bay ADU Regulations are included in Chapter 18.33 of the Municipal Code.


New second dwelling units shall be subject to the same requirements as any single-family dwelling located on the same parcel in the same zoning district, including but not limited to the requirements of coastal development permits and general zoning provisions with the following differences:

A.    Existing Development on Lot.  A single-family dwelling exists on the lot or will be constructed in conjunction with the accessory unit.

B.    Minimum Lot Area per Dwelling Unit.  The minimum lot area per dwelling unit required by the applicable district shall not apply, provided the minimum building site requirements shall be met.

C.    Construction Within or Above Existing Buildings or Detached Accessory Buildings.  A second dwelling unit may be constructed within or above an existing building or detached accessory building.

D.    Occupancy.  The property owner must occupy either the primary or secondary dwelling unit.

E.    Required Off-Street Automobile Parking Spaces.  A minimum of one off-street parking space for the second dwelling unit, in addition to the spaces required for the primary residence, shall be provided.  All off-street parking spaces for the second dwelling unit may be uncovered but must be paved per the city’s parking ordinance, provided exceptions for off-street parking requirements shall be subject to the granting of an exception approved in accordance with this title.  Off-street parking shall be permitted in setback areas or through tandem parking, unless specific findings are made that parking in setback areas or tandem parking is not feasible based upon topographical conditions, fire and life safety conditions, or that it is not permitted anywhere else in the jurisdiction.

F.    Maximum Unit Size.  The floor area of the second dwelling unit shall not exceed seven hundred square feet.

G.    Minimum Unit Size.  The minimum floor area of the second dwelling unit shall be no less than one hundred fifty square feet or the minimum required for an efficiency dwelling unit as defined in Section 17958.1 of the Health and Safety Code, as may be amended from time to time.

H.    Setbacks for Detached Second Dwelling Units.  Detached second dwelling units shall have a minimum side setback of five feet and minimum rear setback of ten feet.  The distance between buildings on the same lot must be a minimum of six feet.  If any portion of a second dwelling unit is located in front of the main building, then the front and side yard setbacks shall be the same as a single-family dwelling in the zoning district.

I.    Setbacks for Attached Accessory Dwelling Units.  Attached accessory dwelling units shall meet the same setbacks as a main building in the zoning district.


M.    Architectural and Site Design Standards.  Architectural and design standards are limited to the following:

1.    The design of the second dwelling unit shall relate to the design of the primary residence by use of the similar exterior wall materials, window types, door and window trims, roofing materials and roof pitch.

2.    For second dwelling units located outside the standard side and rear yard setbacks for the district, the entrance to the second dwelling unit shall face the interior of the lot unless the second dwelling unit is directly accessible from an alley or a public street.

3.    For second dwelling units attached to the main dwelling unit, new entrances and exits are allowed on the side and rear of the structures only.

4.    Windows which face an adjoining residential property shall be designed to protect the privacy of neighbors; alternatively, fencing or landscaping shall be required to provide screening.

5.    The site plan shall provide open space and landscaping that are useful for both the second dwelling unit and the primary residence.  Landscaping shall provide for the privacy and screening of adjacent properties.


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