Accessory Dwelling Unit (ADU) City Regulations

Are ADUs allowed in Belmont:


Number of ADUs allowed:

One ADU is allowed on parcels on which only one dwelling unit is located.

Types of ADUs allowed:

Detached, attached and junior ADUs are all permitted.

Lot size:

ADUs are allowed on lots with a minimum of 5,000 sq. ft., however, under a Conditional Use Permit an ADU may be permitted on a lot that doesn't meet the 5,000 sq. ft. guideline.

ADU size:

An ADU of up to 275 square feet is allowed with approval of a standard building permit. However, an ADU not exceeding 50% of the total habitable floor area of the primary dwelling is allowed with approval of a building Page 2 of 5 permit if it meets the following criteria: (1) A detached unit not greater than 399 sq. ft. (2) An attached unit not greater than 640 sq. ft.


Refer to the requirements of the underlying residential zone.


The property is required to meet the parking space and standards for secondary dwelling units in Section 8. Spaces must meet the size requirements in Section 8.3.1 and must be paved and located wholly upon the property, except as provided in Section 8.2.6. Tandem driveway, garage or carport parking spaces may be permitted.

Fire Safety:

Must meet state requirements.

Shape, materials and style:

ADUs must share architectural compatibility with the primary residence. This includes exterior color palettes, materials, and characteristics.


Refer to underlying residential zone requirements.

Design review:

Must meet ministerial review process per state requirements. ADU additions, both attached and detached, shall comply with the following design standards: ADU additions must comply with the Residential Design Criteria (RDC) if the new construction includes: 1) ground floor plate height exceeding 12 feet or roof height exceeds 18 feet (as measured from finished grade); or 2) creates or expands an upper floor. An ADU shall be constructed with facade materials identical in color, and similar in texture and appearance to the primary dwelling, including but not limited to roofing, siding, and windows and doors. ADUs shall match the roof pitch/form of the primary dwelling in order to blend with the architecture of the primary dwelling.

Permit Fees:

Please refer to


ADUs larger than allowed with a building permit under subsections (c) and (d) are permitted providing approval of single family design review and a Second Unit Floor Area Exception under Section 24.5. Floor area exceptions, see Section 5 (24.5) here:

Allowed Zones:

The secondary dwelling unit must meet all site area, density, height and yard area standards of the R-1 zoning district.


Secondary dwelling units are allowed in conjunction with a single family dwelling located in the following residential zoning districts: (a) R-1, R-2, R-3, and R-4 Districts. (b) HRO Hillside Residential & Open Space districts upon approval of a Conditional Use Permit by the Planning Commission.

For more Belmont ADU information:

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