San Mateo ADU Guide (Updated)

City ADU Guides
Written By George Dy

A Comprehensive Guide to ADU Regulation and Zoning Policy in San Mateo, CA

He-yo, San Mateo 👋🏻

We are incredibly thrilled to start shipping accessory dwelling units to San Mateo this year. Across the board, both San Mateo County and San Mateo (City) have been incredibly supportive and progressive about the implementation of accessory dwelling unit ordinances dating beyond the initial passage of SB13.

While providing support for secondary units, San Mateo has also advocated for the preservation of coastal properties in its region with ordinance updates, which are critical to striking a balance between the development of infill housing projects and regional preservation efforts.

If you’re building or planning to build in San Mateo and can’t find the information you’re looking for in our permitting guide, you can visit San Mateo’s ADU support pages here:

General Notes on San Mateo ADU Regulation

  • San Mateo has currently updated it’s local planning requirements to reflect adjustments with compliance with the State ADU Mandate on January 2020

  • Recent 2019 updates to the California Building Code and California Residential Code are in effect

  • Bay Modular’s pre-approved Solo ADU Series is designed to meet the State ADU Mandate and is 100% compliant with the 2019 CBC/CRC

  • All Solo ADUs are pre-approved by the State of California Department of Housing and Community Development (HCD #1560585) and do not require any additional local plan check, inspection, or approval

  • All site preparation, foundation work, and utility upgrade & connection related to the installation of all Solo ADUs will still require local plan check, and inspection

  • Due to statewide updates to ADU regulations, it has never been easier or more affordable to build a permitted ADU

City of San Mateo: Planning Department Contact Information

City of San Mateo, Planning Department
330 West 20th Avenue
San Mateo, CA 94403
Phone: (650) 522-7212
Email: planning@cityofsanmateo.org

 

Detailed San Mateo City ADU Regulations & Guidelines

ADU Size Restrictions (Updated January 2020)

  • ADUs: The Floor Area for a detached ADU shall not exceed 1,200 square feet. If there is an existing primary dwelling, the Floor Area of an attached ADU may not exceed 50% of the existing primary dwelling.

  • Junior ADUs: A unit that is no more than 500 square feet in size and contained entirely within a single-family residence.

Lot Size Restrictions (Updated January 2020)

  • There is no minimum lot size for an ADU so long as a legal Single Family or Multi-Family Residence exists on the property.

Type of ADUs Allowed

  • Detached ADU, attached ADU, and junior ADUs are all approved (Solo ADU Series are detached ADUs)

  • ADUs may be new construction or conversion of existing space (e.g. garage)

  • Junior ADUs must be conversion of existing space (e.g. garage)

  • California Building Code (CBC) & California Residential Code (CRC) 2019 is in effect

Number of ADUs Allowed (Updated January 2020)

  • Except as otherwise permitted by this subdivision, one ADU is permitted per residential lot. Single family residential lots may be permitted up to one ADU and one junior ADU.

  • Multi-family buildings may add ADUs up to 25% of the existing unit space (example: 4-

    unit building would be allowed one ADU), or at least one (1) ADU.

    • These ADUs must meet building code requirements and the existing space must not be currently used for living (storage units and garages would qualify)

    • Spaces required as part of a condition of approval or zoning requirement (e.g. long-term bike storage room) cannot be converted

    • Not more than two detached units may be added to a lot with a multi-family building if no more than 16 feet high with 4-foot side and rear setbacks

Zoning Requirements (Updated January 2020)

According to state law, all residential zoning districts, including single-family and multi-family, are allowed to build ADUs.

Setback Requirements (Updated January 2020)

  • The maximum required setback for a detached new construction ADU shall be no more than 4 feet from the rear and side property lines, 6 feet from the primary dwelling

Parking Requirements (Updated January 2020)

  • No parking for an ADU is required if:

    • Within ½ mile walking distance of public transit

    • Located within an architecturally and historically significant historic district

    • ADU is part of the proposed or existing primary residence or accessory structure

    • When on-street parking permits are required but not offered to the ADU occupant

    • When there is a car share vehicle located within one block of the ADU

  • No parking is required for a junior ADU

  • No replacement parking for the primary residence is required when a garage, carport or

    covered parking is converted to an ADU or is demolished to provide an area for an ADU

Fire Safety Requirements

  • The ADU shall not require fire sprinklers unless they are already installed in the primary dwelling or the property is located in a special fire or hillside overlay, in which case, they may be required.

Architectural Requirements

  • None specified.

  • Interior conversions of existing space are not subject to this requirement.

Height Requirements

16 feet

Ownership (Updated January 2020)

Through 2025, owner occupancy requirements will not apply to new ADUs, per SB13. Owner may rent out both the ADU and primary residence.

Rental Restrictions

  • Rentals for fewer than 30 days are prohibited.

Utility Connections

  • For detached ADUs, the City may require a new or separate utility connection directly between the accessory dwelling unit and the utility.

  • The new connection may be subject to a connection fee or capacity charges based on either square footage or number of drainage fixtures is required. However, any connection fee or capacity charge shall be proportionate to the burden of the proposed accessory dwelling unit, based upon either its size, square footage or the number of its plumbing fixtures.

Fees

  • No impact fees can be charged for units less than 750 square feet. Impact fees for an accessory dwelling unit of 750 square feet or more shall be charged proportionately in relation to the square footage of the primary dwelling unit. Such units must have an independent exterior access from the existing residence, and provide side and rear setbacks sufficient for fire safety.

  • Additional details specific to ADU projects can be found in the fee schedule here: https://www.cityofsanmateo.org/DocumentCenter/View/67540/2019-20-Adopted-Comprehensive-Fee-Schedule?bidId=

George Dy
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