Print
Press Enter to show all options, press Tab go to next option

Accessory Dwelling Units (ADUs)

On May 23, 2017, the City Council adopted Ordinance No.: 2017-1118, which amended the development standards and review process for accessory dwelling units (Section 24 of the Belmont Zoning Ordinance).  The amended ADU standards are summarized below.   

Accessory Dwelling Unit (second unit, granny unit)

An ADU is a secondary dwelling unit with complete independent living facilities for one or more persons (i.e., permanent provisions for living, sleeping, eating, cooking, and sanitation); it generally takes three forms:

➤  Detached: The unit is separated from the primary structure

➤  Attached: The unit is attached to the primary structure

➤  Interior: The unit is comprised of existing space within the primary residence or an accessory structure (i.e., a guest bedroom is converted into an independent living unit). 

Note: An ADU may consist of an efficiency unit, as defined in Section 17958.1 of Health and Safety Code (minimum of 150 sq. ft.); or a manufactured home, as defined in Section 18007 of the Health and Safety Code.

Standards for ADUs

The City has only ministerial standards for ADUs.  Ministerial standards do not require discretionary review (i.e., Conditional Use Permits and/or Single-family Design Review). ADU applications meeting the ministerial standards can be approved with building permit.  The main standards for the different types of units are summarized below.  A full list of the ADU standards is provided in Section 24 of the Belmont Zoning Ordinance. 

General Provisions - The following provisions apply to all ADUs: 

  • There is no minimum lot size.

  • The project site is zoned for residential use (Single or Multi-family), including R-1, R-2, R-3, R-4, R-5, Hillside Residential and Open Space (HRO), and residential Planned Developments (PD) Districts.

  • There is a single-family dwelling (SFD) on site.

  • There is only one ADU permitted on site.

  • The ADU cannot be sold separately.

  • No Parking is required for the ADU unless it replaces an existing garage, carport or uncovered parking area. 

  • Neither the ADU nor the SFD may be used for short-term residential rentals.

  • Either the SFD or the ADU must be owner-occupied if the home and ADU are occupied by different families.

  • An accessory dwelling unit must include no less than the minimum floor area identified for an efficiency unit, as defined in Health and Safety Code Section 17958.1 (currently 150 sq. ft.).

Interior Unit – In addition to the General Provisions, the following provisions also apply to interior accessory dwelling units: 

Zoning Standards & Access

  • The zoning standards of the underlying zoning district (e.g., setbacks, height, floor area ratio, etc.) do not apply to interior accessory dwelling units. 

  • The ADU must be constructed entirely within the existing and legally created space of a single-family home or accessory structure in an R-1, Hillside Residential and Open Space (HRO), or residential Planned Developments (PD) District.

  • An interior ADU must have exterior access independent from the existing single-family home.

Setbacks

  • Side and rear setbacks of the structure in which the interior ADU is located must be sufficient for fire safety, as determined by the Fire Marshal.

Utilities

  • New or separate utility connection directly between the accessory dwelling unit and the utility may not be required.

Attached Unit – In addition to the General Provisions, the following provisions also apply to attached accessory dwelling units:

Zoning Standards

  •  Except as modified by Section 24, an ADU attached to the primary dwelling unit shall conform to all requirements of the underlying residential zoning district, any applicable overlay district, and all other applicable provisions, including height, setback, floor area ratio, and historic preservation requirements.

Floor Area

  •  The increased floor area of an ADU attached to the existing single-family home shall not exceed the lesser of fifty percent of the living area (as defined in Section 65852.2) of the existing single-family home or 800 square feet. By the current definition, living area includes basement, but not garage or accessory structures

Utilities

  •  Separate utility connections between the accessory dwelling unit and all utilities, and connection fees/capacity charges may be required, consistent with Government Code Sections 66000 and 66012.

Design

  •  An attached ADU must comply with the following design standards:

a)      The ADU must comply with the Residential Design Criteria (RDC) if the new construction includes: 1) a ground floor plate height that exceeds 12 feet or a roof height that exceeds 18 feet (as measured from finished grade); or 2) creates or expands an upper floor.  

b)    The ADU must be constructed with compatible/complementary facade materials, generally the same color palette, and similar in texture and appearance to the primary dwelling, including but not limited to roofing, siding, windows, and doors.

c)     The ADU roof pitch/form must be compatible with the roof pitch/form of the primary dwelling.

Detached Unit – In addition to the General Provisions, the following provisions also apply to detached accessory dwelling units:

Zoning Standards

  •  Except as modified by Section 24 and as identified below, a detached ADU must conform to all requirements of the underlying residential zoning district, any applicable overlay district, and all other applicable zoning provisions, including height, setback, floor area ratio, and historic preservation requirements.

Setbacks.

(A)     A detached accessory dwelling unit must be located no less than five feet from the primary dwelling unit on site. 

(B)    The minimum side setbacks for a detached ADU is five feet from interior side lot lines and fifteen from street side lot lines of corner lots (See Detached ADU Setbacks).

(C)    On reverse corner lots, a detached ADU may not project beyond the inner line of the front yard required on the adjacent lot to the rear, nor be located less than five feet from the side lot line of such adjacent lot.

(D)    The minimum rear yard setback for a detached ADU is five feet.

(E)    Notwithstanding subsections (A) through (D), the minimum setbacks for an ADU that is constructed above an existing garage is five feet from the rear and side property lines (including street side corner lots and reverse corner lots). 

Height.

(A)    A one story detached ADU may be up to 15 feet in height.

(B)    A detached ADU constructed over a garage or other accessory structure where the ADU would be five feet from the rear or side lot line may be up to 17 feet in height when such unit has a flat roof.

(C)    A detached ADU constructed over a garage or other accessory structure where the ADU would be five feet from the rear or side lot line may be up to 20 feet in height when such unit has a pitched roof.

(D)    A detached ADU constructed over a garage or other accessory structure where the ADU would meet the side and rear yard setbacks of the underlying zoning district may be up to 20 feet in height when such unit has a flat roof.

(E)     A detached ADU constructed over a garage or other accessory structure where the ADU would meet the side and rear yard setbacks of the underlying zoning district may be up to 24 feet in height when such unit has a pitched roof.

Floor Area

  • The maximum floor area of a detached ADU is 800 square feet.

Utilities

  •  Separate utility connections between the ADU and all utilities, and connection fees/capacity charges may be required, consistent with Government Code Sections 66000 and 66012. 

Design

A detached ADU must comply with the following design standards:

a)   The ADU must comply with the Residential Design Criteria (RDC) if the new construction includes: 1) a ground floor plate height that exceeds 12 feet or a roof height that exceeds 18 feet (as measured from finished grade); or 2) creates or expands an upper floor. 

b)   The ADU must be constructed with compatible/complementary facade materials, generally the same color palette, and similar in texture and appearance to the primary dwelling, including but not limited to roofing, siding, windows, and doors.

c)   The ADU roof pitch/form must be compatible with the roof pitch/form of the primary dwelling.

For ADU application requirements, please click here. A downloadable PDF version of this document can be found here.