San Mateo is preparing for potential changes to its ADU ordinances following the loosening of state restrictions that will affect city regulations by gathering public feedback.

Phillip Brennan, an associate planner with the city, said the changes to accessory dwelling units, or ADUs, are part of a larger purpose from the state’s perspective to facilitate another way to address housing needs. Brennan said the public feedback would help develop new local ordinances that will go to the City Council for approval later this summer.

“There’s a lot of interest in our city and throughout the state regarding accessory dwelling units, and the primary reason for that is in January 2020, several new ADU housing bills came into law, which took aim at easing local zoning controls, reducing fees and expediting the permitting process,” Brennan said.

A community workshop on the ADU ordinance update occurred June 26, with another one taking place two days earlier. ADUs are attached or detached units often called second units, in-laws or “granny units.” A junior accessory dwelling unit, or JADU, is contained entirely within a single-family residence and has access to the home but has an entrance. It can share bathroom facilities with residents.

ADUs are ways to accommodate older family members or young people beginning their professional careers, adding additional income or maximizing unused space. Brennan noted development increases housing stock in the city and helped address regional housing needs.

Brennan said the existing local ordinance is not in complete compliance with all new state regulations, and the city said the ordinance sections in conflict are being defaulted to state regulations. Development types include an attached ADU, which is attached to the primary residence and, under state regulations, allow it to be up to 50% of the primary resident’s size. Detached ADUs can be up to 1,200 square feet under state regulations, providing there is enough floor area allowance remaining on the lot. Conversion ADUs are contained entirely within an existing residence or accessory structure. JADUs must be entirely contained within the footprint of a single-family home and be a maximum of 500 square feet. State requirements call for one off-street parking space per ADU or bedroom, whatever is less. Converting or demolishing a garage or carport while developing an ADU in its place no longer requires replacement parking. Multifamily ADUs are allowed within nonliving spaces within a multifamily structure, with up to 25% of existing units eligible for conversion.

The San Mateo City Council in April held off on an ADU ordinance imposing stricter regulations to height and size requirements, instead opting for a public input process before approval.

Brennan noted the state-required minimum building ADU height is 16 feet, which promoted questions from the public about its meaning for builders.

“It’s not saying that property owners are obligated to build an ADU of at least 16 feet in height. All it’s saying is that a local agency such as the city of San Mateo cannot impose any development standard that would require someone to build an ADU less than 16 feet,” Brennan said.

Brennan said the city would have internal discussions about preapproved design programs for ADUs. Poll questions were asked to the public that will help develop a new local ordinance. Questions included how tall detached ADUs should be and what design features should match the primary home. Attendees in the workshop noted matching the design to the primary home was not of great importance. Other questions touched on privacy impacts and restriction conditions.

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(2) comments

Thomas Morgan

In the short run, you get a housing unit. The down side is whenever the homeowner decides to sell you just made a single family home $600K-$800K more expensive.


We should be really concerned about the fact that the state legislature is hammering away at cities' rights to regulate zoning.

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