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CITY OF SAN MATEO
Agenda Report
City Hall
330 W. 20th Avenue
San Mateo CA 94403
www.cityofsanmateo.org
Agenda Number: 17 Section Name: PUBLIC HEARING Account Number: 25-3112 File ID: 26-10814 TO: City Council
FROM: Alex Khojikian, City Manager
PREPARED BY: Community Development Department
MEETING DATE: January 26, 2026
SUBJECT:
Accessory Dwelling Unit Ordinance - Zoning Code Amendments — Ordinance Introduction RECOMMENDATION:
Introduce an Ordinance to amend San Mateo Municipal Code Chapter 27.19, “Accessory Dwelling Unit and Junior Accessory Dwelling Unit – Residential Zones” to address comments from the California Department of Housing and Community Development (HCD) to align with current state law, and to address Housing Element programs, and find it exempt from CEQA pursuant to Section 21080.17 of the Public Resources Code and Section 15282(h) of the CEQA Guidelines.
BACKGROUND:
Since 2016, the State Legislature has passed several state laws to streamline permitting and promote construction of Accessory Dwelling Units (ADUs) across California. The City of San Mateo adopted its current local ADU Ordinance on March 21, 2022 to implement local regulations for ADUs in alignment with State law, and with City Council directing staff to provide annual updates on implementation. Since adoption in 2022, the City has seen significant ADU permitting and construction activity, with over 300 permits issued (164 of which have been finalized) over the past three and half years (an average of 87 permits issued per year).
As part of the City’s adopted Housing Element (2023-2031), the City prioritized increased ADU production (Policy H1.4) and supported it with six implementation actions, including an action focused on amending the City’s ADU Ordinance to align it with current State law and to resolve any inconsistencies identified by the California Department of Housing and Community Development (HCD). HCD has had statutory authority to review local agencies’ ADU Ordinances since 2016, and as of January 1, 2024, also has authority to enforce all State ADU laws. In October 2024, the City received a letter from HCD summarizing the agency’s review of the City’s ADU Ordinance (Attachment 3). The HCD letter identified specific ordinance provisions requiring updates or clarification. An official City response letter was sent to HCD in November 2024 (Attachment 4), with a stated goal to update the ADU Ordinance by the end of 2025.
In January 2025, HCD also published an updated ADU Handbook1 addressing frequently asked questions and summarizing recent changes to State ADU law. One notable change is Senate Bill (SB) 1211, effective January 1, 2025, which allows for up to eight detached ADUs to be constructed on a lot with an existing multifamily dwelling, provided that the number of ADUs does not exceed the number of existing units on the lot.
On August 26, 2025, a Planning Commission study session was held to introduce ADU Ordinance updates and receive Commission feedback. There were a total of four public comments submitted in writing and three public speakers provided verbal comments (two of which also submitted their comments in writing). The comments are included as 1 ADU Handbook link
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Attachment 5.
During this study session, the Planning Commission provided staff with feedback on specific local changes, outside of those required for State law compliance, in order to address community needs. Following the study session, staff conducted outreach and hosted a virtual workshop on local ADU regulations and proposed changes on September 25, 2025. The workshop included a staff presentation, polling questions to collect information and feedback, and time for attendees to ask questions related to the proposed ADU Ordinance update effort. Information related to this policy effort is included on the City’s Policy and Zoning Code Update page.
On December 9, 2025, the Planning Commission held a public hearing to consider the updated ADU Ordinance. There was one comment submitted in writing and no public speakers provided verbal comments at the meeting. The written comments provided were from the California Housing Defense Fund (CalHDF) regarding ADU size limits, parking, and the ADU Discretionary Review process (Attachment 5). Based on the fact that HCD has reviewed and provided input on the draft ADU Ordinance and did not raise concerns with any of the items noted by CalHDF, staff did not identify any changes that were legally required based on this comment letter.
Following the staff presentation and deliberation, the Commission voted to recommend approval of the updated ADU Ordinance with one modification proposed by staff and three additional modifications for City Council consideration.
These recommendations are as follows:
1. Per staff recommendation, amend Section 27.19.070 to add the following subsection: 27.19.070(b)(2)(C) “Any additional ADUs as allowed pursuant to State law”.
2. ADU Discretionary Review (ADUDR) application appeals in Section 27.19.045 should be heard by the Planning Commission, and if appealed again, by City Council. This is in conformance with other appeals procedures in the Zoning Code (Title 27), and was recommended by the Planning Commission, rather than for appeals to be heard by the City Manager or their designee.
3. Clarify Section 27.19.045 to state that the ADUDR process may be used to review an ADU proposal that is not compliant with any objective standard in the ADU Ordinance, with the exception of FAR maximums.
4. Change the standard for location of second story decks or balconies proposed with an ADU in Section
27.19.060(h)(5) to state that the deck or balcony “shall not face adjacent residential properties.” DISCUSSION:
Proposed Ordinance Amendments
The proposed ADU Ordinance amendments are included in the Draft Ordinance (Attachment 1). A version with tracked changes to show where edits have been proposed to the existing ADU Ordinance text is also included as Attachment 2.
Some of these edits are more minor/structural to improve organization for clarity, while others would result in a change to existing ADU development standards. A complete summary of those changes that result in a new or changed ADU development standard is given below.
Changes Proposed in Response to HCD Comments and State Law Compliance The changes listed below have been made primarily to address specific comments provided by HCD in their review of the City’s ADU Ordinance. These changes include updates to areas of the Ordinance either that are inconsistent with State ADU law, or where additional clarification was requested by HCD to demonstrate State law compliance.
1.ADU Definition
HCD commented that the City’s ADU definition only includes reference to single-family ADUs. This is inconsistent with State law, as ADUs must be allowed on lots with single-family or multifamily dwellings. In response, the ADU definition has been revised to clarify that ADUs are allowed on lots with either single-family or multifamily dwellings.
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2.Multifamily Dwelling Structure Definition
The City’s zoning ordinance currently distinguishes between two-family and multifamily dwellings in a manner that is not fully consistent with State ADU law. To resolve this, the City added a new definition of “Multifamily Dwelling Structure” applicable only to ADU development, consistent with State law, to clarify that a multifamily structure consists of two or more attached primary dwelling units.
3.Allowance for Separate Sale of ADUs per Government Code Section 66341 The City’s existing ordinance prohibits ADUs from being sold separately from the primary residence, with no exceptions specified. HCD identified that this is inconsistent with Government Code Section 66341, which requires that the City allow for separate sale of ADUs that are built or developed by a qualified nonprofit corporation, with additional specific qualifying criteria. Therefore, the update references this statute to allow for separate sales of ADUs, only when specified criteria are met.
4.Proportionality for ADU Impact Fees
The City’s existing ordinance allows ADU impact fees to be set by City Council resolution. HCD noted that the ordinance should clearly reflect State law by exempting ADUs under 750 square feet from impact fees and requiring proportional fees for larger ADUs. The ordinance has been revised to explicitly incorporate these requirements.
5.Utility Fee Clarification
Separate from impact fees, State law allows for a jurisdiction to charge a connection fee or capacity charge for utilities. This charge must be proportionate to the burden of the proposed ADU, based either on square footage or number of drainage fixture unit values. Currently, the City’s ADU Ordinance does include a provision to require payment of a connection fee or capacity charge for ADUs that are separate from an existing structure. However, this connection fee or capacity charge may only be imposed when an ADU is constructed with a new single-family dwelling. Therefore, language has been added to clarify that, “An ADU shall not be considered a new residential use for the purposes of calculating connection fees or capacity charges for utilities, including water and sewer service, except when the ADU is constructed with a new primary residential dwelling unit.”
6.Removal of Reference to Variance Process
The City’s existing ADU Ordinance includes a statement that, “All other zoning requirements shall be complied with unless an authorized variance is approved.” HCD commented that the City should amend the Ordinance to “bolster clarity regarding the ADU approval process,” which must provide for ministerial review under State law.
This reference to the variance process has been removed from the ADU Ordinance.
7.Number of ADUs Permitted with Single-Family
HCD has now interpreted that State law requires that single-family lots be allowed to develop up to three types of ADUs, as is reflected in Government Code Section 66323. The three required types are:
a. One Attached or Conversion ADU (from existing or proposed space within a structure); b. One Detached New Construction ADU; and
c. One JADU, located within the walls of an existing or proposed Single-Family Dwelling.
HCD’s January 2025 ADU Handbook (p. 19), confirms that all three types must be allowed concurrently when a lot has an existing or proposed single-family dwelling, and local agencies may not restrict a property to fewer than these three units if each meets the applicable development standards. Current City regulations allow only two ADUs (one ADU and one JADU). To comply with State law and HCD’s interpretation, the ADU Ordinance will now allow up to three ADUs on a single-family lot.
8.Front Setback Clarification
HCD commented that the City may not impose a front setback requirement that would preclude construction of an ADU of up to 800 square feet with four-foot side and rear setbacks. Under current local ADU regulations, all new construction ADUs are subject to the front setback of the underlying zoning district. Therefore, language has been added to clarify that “no front setback is required for a State Exempt ADU.” The City may still impose a front
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setback on other new construction ADUs that are not considered state-exempt units. “State Exempt ADU” means an accessory dwelling unit that is created pursuant to Government Code Section 66323. This includes conversion ADUs within an existing single-family residence or accessory structure, as well as a new detached ADU of not more than 800 square feet, with four-foot side and rear setbacks.
9.Architectural Standards – Not Applicable to State Exempt ADUs The City’s existing ADU Ordinance includes several architectural standards for ADUs. HCD provided a comment to clarify that these architectural standards may not preclude development of “State Exempt ADUs.” This has been addressed in the update, which includes definitions of “State Exempt ADUs” and “Nonexempt ADUs”, and clearly states that the architectural standards shall only apply to Nonexempt ADUs.
10.Design Standards – Removal of Subjective Standards
State ADU law allows for local ordinances to impose only objective standards on accessory dwelling units. In their review of the City’s existing ADU Ordinance, HCD noted that some of the design standards such as requiring similar exterior materials to the main home, and windows that maximize privacy, are subjective in nature and therefore must be either removed or amended to be objective in nature. To address this comment, the subjective standards have been removed.
11.JADU Interior Access Requirements
Under current local requirements, all JADUs are required to have an interior access between the JADU and the single-family dwelling. State law only requires an interior access when the JADU does not include a separate bathroom. City staff met with HCD to discuss these requirements and identified that shared utility controls would also create a need for interior access between units. The update amends the code to specify that interior access is required between the JADU and single-family dwelling when they share restroom facilities and/or utility controls such as a thermostat.
12.Maximum JADU Size
HCD commented that the City’s current JADU size maximum of 650 square feet exceeded the maximum unit size of 500 square feet for a JADU allowed under State law. The update includes a revision to reflect this HCD guidance, reducing the JADU maximum unit size from 650 square feet to 500 square feet.
13.JADU Deed Restriction Requirements
All JADUs are required by State Law to record a deed restriction with the following provisions:
a. A prohibition on the sale of the junior accessory dwelling unit separate from the sale of the single-family residence, including a statement that the deed restriction may be enforced against future purchasers; and b. A restriction on the size and attributes of the junior accessory dwelling unit.
The City’s current ordinance includes provisions consistent with the two listed in State law (above), plus two additional provisions that are included in JADU deed restrictions:
c. The property owner must occupy either the single-family residence or the JADU; and d. If the JADU is rented, the unit shall not be rented for a period of less than 30 consecutive calendar days.
HCD noted that these two additional deed restriction provisions go beyond what is explicitly listed by State law, and therefore must be removed from the City’s deed restriction requirements. However, while not explicitly listed in a JADU deed restriction, the JADU owner occupancy requirement and prohibition on using JADUs for short-term rentals are both still requirements under State law and in the City’s ADU Ordinance.
Assembly Bill 1154, signed by the Governor on October 10, 2025, effective January 1, 2026, amended owner- occupancy requirements to only apply if the JADU has shared bathroom facilities with the existing structure.
Therefore, this requirement has been updated to clarify that owner-occupancy is not required if the JADU has its own bathroom.
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14.Addition of Multifamily ADU Development Standards
The current ADU Ordinance does not include specific standards for multifamily ADUs. Rather, there is a reference within the local Ordinance to Government Code Section 65852.2(e)(1), which previously included standards for multifamily ADU development. However, State Law standards for multifamily ADUs were updated under Senate Bill 1211 and renumbered under Senate Bill 477 thereby making the cross-references the local ADU Ordinance incorrect.
Most notably, SB 1211 included a change to the number of ADUs permitted on a lot with an existing multifamily dwelling. Previously, up to two new detached ADUs were permitted on a lot with an existing or proposed multifamily dwelling. However, this has been updated to allow up to eight new detached ADUs on a lot with an existing multifamily dwelling, provided that the number of ADUs cannot exceed the number of existing primary multifamily dwelling units on the lot. To provide more clarity and reduce the need to cross reference Government Code sections the ordinance update includes a new section for Multifamily ADU Development Standards.
Other Changes Proposed to Address Local Needs and Ordinance Functionality The below changes have been added, in addition to the changes specifically required by HCD, in order to address issues identified by City staff to improve functionality and clarity in implementing the ADU Ordinance. The Planning Commission Study Session on August 26, 2025 and community workshop on September 25, 2025 introduced these topic areas for discussion and feedback to help inform how to proceed with these updates. Based on the input received, below is a summary of the additional proposed changes.
15.Addition of Definitions Section
The ordinance update includes a new section at the beginning of the chapter with ADU-related definitions, with the definitions only applicable to the ADU Ordinance (Chapter 27.19).
16.Updates to Discretionary Review as Alternative to Ministerial Review The City’s existing ADU Ordinance provides two paths for ADU review. The first is a ministerial building permit for any ADU that meets all of the development standards of the Ordinance. The second option is for an Accessory Dwelling Unit Discretionary Review (ADUDR), subject to a Planning Application approved by the Zoning Administrator prior to building permit application for any ADU that is not in compliance with the development standards of the ADU Ordinance.
At the Planning Commission Study Session, staff provided background on the ADUDR process and sought recommendation from the Planning Commission on potentially removing the ADUDR process, paired with more permissive objective design standards for ADU height and allowances for second-story decks and balconies.
The Commission recommended the City keep the ADUDR process in the updated Ordinance as an alternative to ministerial review to provide a pathway for consideration of ADU designs that exceed the specified objective standards to address certain site-specific design needs. The Commission was also in favor of staff’s recommendation to propose more permissive objective standards, expressing support for the idea that these changes would result in more ADU projects qualifying for the more streamlined ministerial review process – the proposed changes to height, setback, and second story deck standards are discussed in more detail below. a.Clarification of ADUDR Applicability – The ordinance update includes added language to clarify that the ADUDR process may be used to review any ADU that is not in full compliance with height, setback, or daylight plane provisions of the ADU Ordinance. However, the ADUDR process may not be used to increase the maximum allowable floor area of an ADU.
i. The Planning Commission recommended updating this language to clarify that the ADUDR may be used to review any ADU that is not in full compliance with any objective standard in the ADU Ordinance, including but not limited to, height, setback, or daylight plane provisions (excluding maximum allowable floor area of an ADU).
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b.ADUDR Requirement for Second-Story Decks and Balconies – Under current ADU Ordinance provisions, any second-story deck or balcony proposed with an ADU requires ADUDR. The ordinance update includes new objective standards for second-story balconies (discussed further below), which would allow for small interior facing second-story decks or balconies to be reviewed ministerially. Any proposed larger second-story decks or balconies that do not meet these objective standards will still require an ADUDR under the ordinance update. c.Updated ADUDR Findings – The ordinance update revises the ADUDR findings to improve clarity, objectivity, and consistency with State law and City policies. More objective findings have been added to address privacy impacts from larger second-story decks, require justification for deviations from height, setback, or daylight plane standards due to site-specific hardship, and confirm consistency with the General Plan, aligning the ADUDR process with other planning applications.
d.Appeal Process for ADUDR – The appeal process for the decision of the Zoning Administrator for an ADUDR had been streamlined in the ordinance update to provide for appeals to the City Manager or their designee, which could be a hearing officer. However, under the current draft Ordinance, the appeal would go to Planning Commission first, and then to City Council if further appealed, consistent with state law. i. The Planning Commission recommended not changing the appeals process to the City Manager or their designee. Instead the current process of the Planning Commission hearing appeals first, and then City Council if further appealed, would remain.
17.Clarification on Max. ADU Unit Size and FAR Exemption for ADUs The City’s current regulations do not include any specified maximum ADU size limit. Any ADU floor area exceeding 800 square feet is regulated by the allowable floor area ratio (FAR) of the underlying zoning. Up to 800 square feet of ADU floor area is exempt from the total FAR calculation for a lot. ADUs cannot exceed the size of the primary residential unit on the property (either the single-family residence, or any individual unit within a multifamily building), with the exception that if the primary residence is less than 800 square feet, an 800 square-foot ADU would still be allowed per State law. The existing maximum unit size standards have not been substantially changed.
Since the December 9, 2025 Planning Commission public hearing, several changes to State ADU law have become effective, including Senate Bill 543 (SB543), which became effective January 1, 2026. SB543 includes an update to specify that requirements for JADU and ADU square footages are based on interior livable space. The proposed update includes a definition for “ADU Living Area” that is consistent with how State law defines interior livable space. To address this change, a minor edit has been made to the draft Ordinance language to refer to “ADU Living Area” in the Maximum Unit Size and Floor Area sections.
18.Height of Detached ADUs
The City’s current ADU Ordinance sets a maximum height for detached ADUs at 16 feet to top plate and 24 feet to roof peak. The ordinance update would increase the plate height requirement by two feet, resulting in a maximum height for detached ADUs of 18 feet to top plate and 24 feet to roof peak, which is consistent with state law. The increase in height allowance would allow for more standard two-story construction. No change is proposed to the height requirements for attached ADUs, which are currently set at 24 feet to plate and 32 feet to peak, consistent with the maximum height requirements for single-family residences.
19.Setback Exception for ADUs in Rear Third of a Lot Meeting Specific Standards The proposed ordinance update would allow ADUs built in the rear one-third of a parcel to use the same zero- setback allowances currently permitted for accessory structures. Under existing zoning, accessory structures in this area may be built to a zero setback if they meet established height, daylight plane, yard coverage, and floor limitations, and these structures may later be converted to ADUs. To streamline ADU production and avoid this two-step process, the Planning Commission supported applying the accessory structure setback standards directly to new ADUs constructed in the rear one-third of a property.
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20.Removal of ADU Parking Requirements
The City’s current ADU ordinance requires one off-street parking space per ADU but includes several State- mandated exemptions, which apply to most properties in San Mateo, such as proximity to transit, location within existing structures, or access to car-share services. HCD also noted an additional required exemption when an ADU is proposed with a new single- or multifamily dwelling. Because these exemptions already cover nearly all ADU- eligible parcels in the City, the ordinance update proposes to eliminate all off-street parking requirements for ADUs to ensure equitable treatment. This change would not materially alter existing regulations, but the updated ordinance would continue to encourage voluntary off-street parking through new supportive provisions, an approach that was discussed at the Planning Commission Study Session and generally supported by the Commission.
21.Additional Voluntary Parking Standards
To support additional creative approaches to encourage voluntary off-street parking for ADUs and to help address the constraints to on-street parking in many residential areas of the City, staff have included additional provisions to incentivize voluntary off-street parking for ADUs and JADUs, as follows:
a. Voluntarily provided parking associated with ADU or JADU development must be located entirely on the same lot, and may be provided in a garage, carport, uncovered, or in tandem orientation. When a garage or carport is converted to an ADU or JADU, or demolished in conjunction with construction of an ADU, the existing driveway and curb cut are not required to be removed and may be maintained as parking area. b. A maximum of up to two voluntarily provided parking stalls may be provided for each ADU or JADU. c. The maximum driveway width for single-car garages may be up to 20 feet to accommodate additional off- street parking.
d. Uncovered parking for an ADU or JADU may be located in the required front, side, and rear yard setback areas. If a covered parking structure is proposed to provide voluntary parking below a second-story ADU, the parking structure may be located within the footprint of the proposed ADU, provided that it is outside of the front yard setback of the underlying zoning district. When a parking structure is proposed within a required side or rear setback of the underlying zoning district, the plate height of the parking structure shall not exceed nine feet in height.
22.Prohibition of Rooftop Decks or Terraces above an ADU A standard has been added in the ordinance update to specify that rooftop decks or terraces above any portion of an ADU are prohibited. This provision is added to clarify a distinction between rooftop decks and terraces, and small second-story decks or balconies.
23.Allowance of Small Second-story decks or balconies with ministerial review if specific standards are met Under the City’s current ADU Ordinance, all second story decks and balconies require ADUDR review. At the Planning Commission Study Session, the Commission provided staff with feedback on this process, expressing support for creating objective standards to allow for some second story decks and balconies to be considered ministerially. The Commission expressed the importance of providing standards that would ensure deck and balcony designs are sensitive to potential privacy impacts to adjacent neighbors. As a part of the ordinance update, staff have proposed that small second story decks or balconies may be considered as part of an ADU design for ministerial review, provided that the following standards are met:
a. Second story decks or balconies shall not be larger than 50 square feet in size. b. No portion of a second story deck or balcony shall be located within the setbacks of the underlying zoning, regardless of the ADU setbacks.
c. Second story decks or balconies shall only face the interior of the subject property.
i. The Planning Commission recommended changing this to instead specify that second story decks or
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balconies shall not face abutting residential properties. The Commission’s recommendation was based on the idea that a deck or balcony facing a street, nonresidential property, park, etc. would not create the same privacy concerns as a deck facing into a neighboring home or residential yard area.
These proposed standards would allow for small second story balconies and decks to be proposed with ADUs considered for ministerial review, while addressing concerns about privacy impacts to adjacent properties. This would also provide for additional streamlining for decks and balconies that meet these standards, reducing the need for ADUDR review. Second story decks or balconies that do not meet these standards could still be considered under the ADUDR process.
NEXT STEPS:
Following introduction, the Ordinance will be brought back for a second reading and adoption at the next available City Council meeting, and the Ordinance will go into effect 30 days afterwards. In addition, the City is required to submit the approved ordinance to HCD within 60 days of adoption for final review and acceptance by the State. If HCD identifies any inconsistencies between the City’s Ordinance and State law, a follow-up code amendment may be necessary. However, based on prior discussions with HCD and internal review, Draft Ordinance appears to be fully consistent with State law.
Once the ADU Ordinance is adopted, staff will update all ADU related handouts, educational materials, and website information to reflect the updated requirements for development of ADUs and JADUs.
BUDGET IMPACT:
Zoning Code Amendments to implement the Housing Element are funded in the Community Development Department’s annual operating budget, utilizing the Advanced Planning Fund (Fund 225), and does not impact the City’s General Fund.
ENVIRONMENTAL DETERMINATION:
The proposed ordinance is statutorily exempt from the requirements of the California Environmental Quality Act (CEQA) pursuant to Section 21080.17 of the Public Resources Code and Section 15282(h) of the CEQA Guidelines because it is an accessory dwelling unit ordinance that is implementing the provisions of the Government Code related to ADUs and JADUs.
NOTICING AND COMMENTS:
All meeting noticing requirements were met. Additionally, staff sent meeting details in the Planning Division eNewsletter, citywide eNewsletter, the Housing Element interested parties list and posted to the Planning Division’s What’s Happening in Development webpage. Prior to this public hearing, notice was also provided in the Planning Division eNewsletter, the citywide eNewsletter, and on City Social Media to advertise the August 26, 2025 Planning Commission Study Session and September 25, 2025 Virtual Outreach Webinar.
Staff has not received any public comments on this item since the Planning Commission public hearing on December 9, 2025. All public comments received prior to this public hearing at included in Attachment 5. Any public comments received after agenda publication will be posted to this item on the City’s Public Meeting Portal as “Post Packet Public Comments.”
ATTACHMENTS
Att 1 – Draft ADU Ordinance
Att 2 – ADU Ordinance (Track Changes)
Att 3 – HCD Review Letter
Att 4 – City Response Letter to HCD
Att 5 – Public Comments
STAFF CONTACT
Elizabeth Gagliardi, Associate Planner
[email protected]
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(650) 522-7206