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Belmont ADUs

Everything about building Accessory Dwelling Units in Belmont, CA

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Belmont ADU Guidelines Last Updated 04/05/20

PLANNING OFFICE The city planning office is not open to the public at this time, but is accepting ADU permit questions and applications.

The city government of Belmont has updated its local zoning codes to comply with the State ADU mandate.
The California Building Code (CBC) 2019 is adopted.
Relevant state bill updates for SB13, AB68, AB881, AB670 are shown in green below.


City Hint: The city has not yet responded to requests for ADU permit volumes for the past year, but they will be provided here once response has been received.

Number of ADUs allowed:

Under state law, each single-family home may now add at least one ADU. Owner occupied single-family lots may add one ADU and one Junior Accessort Dwelling Unit (JADU). Multi-family lots, per every four existing residential units, may add one ADU, so long as the existing units were legally established.

As of January 1st, 2020

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are approved. ADUs may be new construction or converted from existing space. JADUs must be converted from existing space.

Lot size:

Accessory Dwelling Unit (ADU) projects on single family or multi-family residential parcels will not be subject to the minimum lot size of the underlying local zoning code or by special ordinance. ~ AB68 & AB881 Update

As of January 1st, 2020

ADU size:

Single-family and multi-family Properties will be allowed to add up to 850 sq. ft. for a one bedroom ADU or up to 1,000 sq. ft. for a two bedroom ADU, regardless of the underlying zoning standards of the property. A Junior Accessory Dwelling Unit up to 500 sq. ft. is allowed. The minimum size of any living unit (including ADUs and Junior Accessory Dwelling Units) is 150 sq. ft. according to Califronia Residential Code. ~ AB-68

As of January 1st, 2020


Setbacks for a detached new construction Accessory Dwelling Unit (ADU) shall be no more than 4 feet from the rear and side lot lines. No setbacks shall be required for Accessory Dwelling Unit (ADU)s and Junior Accessort Dwelling Unit (JADU)s converted from legally eastablished existing space. Attached new construction Accessory Dwelling Unit (ADU)s and conversions from existing space to be expanded must comply with the setbacks of the underlying zone. ~ AB68 & AB881 Update

As of January 1st, 2020


Lots which convert an existing garage to an Accessory Dwelling Unit or Junior Accessort Dwelling Unit (JADU) will not be subject to replacement parking requirements. ~ According To AB68

As of January 1st, 2020

Fire Safety:

Per state requirements.

Shape, materials and style:

Architectural compatibility with the primary home, including exterior color, materials, and characteristics.


Subject to the requirements of the underlying residential zone.

Design review:

ministerial review process per state requirements.
Design Standards for ADUs (attached and detached ADUs). ADU additions 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 exceeds feet or roof height exceeds feet (as measured from finished grade); or 2) creates or expands an upper floor.
➤ ADUs 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.

Number of Bedrooms:

Not specified by State Standards.


Between between 2020 and 2025, owner occupancy requirements will not apply to new ADUs. (applicable to new construction and conversion units) ~ SB13

As of January 1st, 2020

Utility connections:

Local health officer approval where a private sewage disposal system is being used, if required. (State requirements)

Permit Fees

SB13 Update: As of January 1st, 2020, local impact fees for ADUs will be reduced substantially statewide.


Exception to Maximum Ministerial Unit Size. Second units larger than allowed
with a building permit under subsections (c) and (d) are permitted with 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:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

Authority and Purpose. This section regulates the establishment of secondary dwelling
units in all residential zoning districts in accordance with Government Code Section
65852.2. The purpose of permitting secondary units is to promote more efficient use of
the City's existing housing stock and to help meet the need for small rental units while
preserving the character of the City.

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

As of January 1st, 2020


Location. 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.

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

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ADU Example Designs

ADU Model 288 sqft

W 18 ft L 16 ft

ADU Model 400 sqft

W 20 ft L 20 ft

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CA Statewide

Tailored to ADU construction.
Based on project size & appreciation.
Learn how to qualify.

Karyn Jones

Program Representative

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Costs / ROI



* upon completion of ADU


* based on local average price per sqft


* estimated by location


* 30 years / 5% interest rate / 20% down payment


Size: 500 sqft


Appreciation Estimate = (Base Value: $) / (Home's Living Space: sqft) * (ADU's Living Space: sqft)

Rental Estimate = (Rent Per Sqft: $5.60) * (ADU's Living Space: sqft)

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Expert Feasibility & Zoning Research

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