Item No. 5
Town of Atherton
CITY COUNCIL STAFF REPORT – PUBLIC HEARINGS
TO: HONORABLE MAYOR AND CITY COUNCIL
GEORGE RODERICKS, CITY MANAGER
FROM: BRITTANY BENDIX, CONSULTING TOWN PLANNER
GERRY MARTIN, CONSULTING ASSISTANT PLANNER
DATE: NOVEMBER 19, 2025
SUBJECT: INTRODUCTION AND FIRST READING OF AN ORDINANCE TO AMEND ATHERTON MUNICIPAL CODE CHAPTER 17.52
“ACCESSORY DWELLING UNITS”
CEQA: The project is Categorically Exemption per Section 15305 of the CEQA Guidelines. Section 15305 relates to Minor Alterations in Land Use Limitations, as the ordinance amendments would not result in any changes to land use or density. CEQA Guidelines 15268 (Ministerial Projects) and Public Resources Code Section 21080(b)(1).
RECOMMENDATION:
Staff recommends that the City Council amend Chapter 17.52 “Accessory Dwelling Units” with the purpose of aligning the current standards with state legislation and providing greater clarity during development review.
BACKGROUND
In August of this year the Town initiated an effort to update its Accessory Dwelling Unit (ADU) Ordinance to align with recent changes in state law. On September 24, 2025, the Planning Commission held a public hearing to consider updates to the Accessory Dwelling Unit Ordinance.
The staff report and other attachments for the September 24, 2025 Planning Commission meeting are included in Attachment 1. After discussion, the Planning Commission voted unanimously to approve the staff recommendation to conduct a public hearing to recommend that the City Council amend Chapter 17.52.
Alignment with State Law
Since 2019, the State of California has enacted several laws amending the Government Code Sections relating to regulations of Accessory Dwellings Units (ADUs) and Junior Accessory November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
Dwelling Units (JADUs). The most recent comprehensive update by the Town to align its zoning ordinance with state law occurred in 2024, when the City Council adopted amendments to comply with various bills, including Senate Bills (SB) 1030 and SB 3182, and Assembly Bills (AB) 2221, AB 2097, and AB 976. The 2024 update also included incentives to further ADU growth in an effort to meet the Town’s housing element goals by allowing ADUs to be built above detached garages and establishing a bonus ADU program for lots greater than two acres. Upon adoption of the ordinance the Town submitted its ADU program to the California Department of Housing and Community Development (HCD) and did not receive any request for further changes.
Over the past year and a half, the state legislature has continued to adopt additional refinements to statutes governing the development of ADUs and JADUs. In the event that a local ordinance falls out of alignment with the state and does not continue to comply with new laws, any unique attributes of the local ordinance may become null and void and superseded by the state’s set of standards. This report recommends an update to the Town’s ADU ordinance to maintain its alignment with the following bills adopted by the state legislature in 2024 and 2025:
▪ SB 477 (2024)
▪ SB 1211 (2024)
▪ AB 1332 (2024)
▪ AB 2553 (2024)
▪ AB 462 (2025)
▪ SB 543 (2025)
Clarity During Development Review
As reported in the Town’s Annual Progress Report for 2024, the Planning Department reviewed sixty-two (62) ADU applications in 2024. In addition to actual permits reviewed by the Town, Planning Department staff fields numerous inquiries related to the construction of ADUs and JADUs from property owners, neighbors and prospective developers.
During the implementation of the Town’s 2024 ADU Ordinance, staff has encountered clarity issues with the adopted language specific to ADUs built above a detached garage and direction from HCD on interpreting exactly what “attachment” means for “attached” ADUs. Staff has included changes to these sections to address this confusion.
ANALYSIS
The following are summaries of the portions of recent legislation that are relevant to the proposed ADU ordinance update. Proposed changes to Chapter 17.52 of the Atherton Municipal Code (AMC) are provided in Attachment 2, which identifies changes in red text, and Attachment 3, which presents a clean version of the proposed text inside of the Draft City Council Ordinance.
Attachment 4 includes current state law as it relates to ADUs and JADUs, inclusive of AB 462 (2025) which was integrated into the Government Code as of October 10, 2025. SB 543 (2025) will go into effect on January 1, 2026 and therefore is not currently reflected in the Government Code. Attachment 5 includes the adopted language from SB 543 and identifies through tracked changes how the bill layers on top of existing state law.
The list below identifies the section areas in AMC 17.52 that include recommend changes. While this list addresses most sections in the chapter, many changes are minor or clerical in nature. The November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
analysis in this report provides a summary of the revisions organized by the related bill and topic area.
1. Definitions
2. Maximum Number of Units
3. Floor Area Requirements
4. Exemptions from Maximum Floor
Area Requirements
5. Setback Requirements
6. Entrance Requirements
7. Height
8. Heritage Tree Ordinance
9. Privacy, Screening and Landscaping
10. Lighting Restrictions
11. ADU Rental
12. Passageways and Internal Connections
13.Certificate of Occupancies
14. Application Review
Senate Bill 477
Renumbering of ADU and JADU Government Code Sections
This change simply renumbers and consolidates the sections of the Government Code that regulate ADUs and JADUs from sections 65852.150, 65852.2, 65852.22, 65852.23 and 65852.26 to sections 66310 through 66342. The Town’s ADU Ordinance references the Government Code sections with the purpose of clearly aligning with state law. This is especially useful as the state must review each local ADU ordinance and ensure that ADUs meeting state minimum standards are protected. The state refers to these types of ADUs as 66323 units, referring to the new section number. In response to SB 477 staff has updated Government Code references to match the new numbering adopted by the state.
Senate Bill 1211
Limitation on Local Objective Design and Development Standards This bill prohibits jurisdictions from imposing objective design and development standards on certain types of ADUs protected by the state in Government Code Section 66323(a). As noted above these state-exempt units are denoted in state documents, such as the 2025 ADU Handbook produced by HCD, as “66323 units.” The list below includes a general summary of what types of ADUs are considered 66323 units:
1. One JADU of 500 square-feet inside a single-family home.
2. One ADU converted from space within a single-family home or an accessory structure on a single-family lot, or one ADU attached to a single-family home that is 800 square feet or less.
3. One detached ADU on a single-family lot that is 800 square feet or less, meets height limits ranging from 16 to 20 feet depending on the site’s proximity to transit, and that provides 4-foot side and rear setbacks.
4. ADUs converted from space within an existing multifamily dwelling, not exceeding 25% of the existing number of multifamily units.
5. Detached ADUs on multifamily lots that meet height limits ranging from 16 to 20 feet depending on the site’s proximity to transit, and have 4-foot side and rear setbacks. On a lot with an existing multifamily dwelling, no more than 8 or the number of existing November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
multifamily units, whichever is less, are allowed. On a lot with a proposed multifamily dwelling, no more than 2 detached ADUs are allowed.
Changes to the Atherton ADU ordinance are proposed to address SB 1211 as the current AMC (Atherton Municipal Code) includes objective design and development standards that the Town can no longer apply to state-exempt ADUs. In the affected sections, staff has removed and added language to specify that state-exempt ADUs are not subject to local objective standards more restrictive than what is outlined in state law. This update includes changes in language that address the following requirements:
1. Entrance Requirements. Requirements that the exterior entrances to proposed ADUs face the interior, side, or rear of the lot may only apply to non-state exempt ADUs.
2. Heritage Tree Ordinance. The current AMC code standards exempt some, but not all of the 66323 units. Clarification was added to this section.
3. Privacy, Screening, and Landscaping. Landscape screening, screening design techniques, and the installation of 8-foot tall fencing along the full property line may only apply to nonstate exempt ADUs. The amendments clarify exemptions for 66323 units. Given the Town’s pattern of screening along a shared property line, staff has maintained the 8-foot tall fencing language as an option for property owners, as the AMC generally limits side and rear yard fencing to 6 feet maximum height.
4. Lighting Restrictions. Shielded or downlit exterior lights cannot be required on 66323 units. The amendments clarify this exemption.
5. Passageways and Internal Connections. This amendment clarifies that an internal connection between a state-exempt unit and an accessory building is allowed if the two buildings share a wall.
Number of Allowed Detached ADUs on Multifamily Lots
SB 1211 increases the number of allowable detached ADUs on a lot with an existing multifamily dwelling from two detached ADUs to eight detached ADUs, provided that the number of ADUs does not exceed the number of existing units on the lot.
Assembly Bill 1332
ADU Preapprovals
AB 1332 required every jurisdiction in California to establish a program by January 1, 2025 to review and preapprove ADU plans. In this program an architect can submit a general ADU plan, submit to a local jurisdiction for preliminary approval and then sell plans as “preapproved.” The availability of preapproved plans is considered a potential cost savings for a property owner.
However, the actual permit submittal would still require a site plan specific to the subject property and information specific to the site’s soils and foundation needs.
Local agencies are required to post the preapproved plans and applicant (designer) contact information on their website. Additionally, jurisdictions must approve or deny applications using the pre-approved plans within 30 days. Atherton has complied with AB 1332 and created such a program. The proposed amendments clarify the review and approval time limits set by this bill for permit applications that use preapproved plans.
November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
Assembly Bill 2553
Major Transit Stop Definition
This bill revises the definition of “major transit stop” by increasing the frequency of service interval from 15 minutes to 20 minutes or less during peak commute periods. It also expands the definition to include bus rapid transit to the list of qualifying modes of transit under the definition.
By broadening the definition, this allows for more ADUs to take advantage of the increased height limit when in proximity to qualifying transit stops, making it feasible to build 2-story ADUs.
Assembly Bill 462
Certificate of Occupancy
This bill requires a local agency to issue a certificate of occupancy for an ADU even if the certificate of occupancy has not been issued for the primary dwelling, only under specific circumstances. A certificate of occupancy is a document issued by local California Building and Safety departments (the Building Department for Atherton) which certifies that a commercial space or newly constructed residential building has been inspected for compliance with the California Building Standards Code and local ordinances which govern construction and occupancy. The current language in the Atherton ADU ordinance allows a certificate of occupancy for an ADU to be issued only after one has been issued for the primary dwelling. Under AB 462, an ADU can receive a certificate of occupancy prior the primary dwelling if the Governor has declared a state of emergency for the county the jurisdiction is located in, and the primary residence was substantially damaged or destroyed due to an event related to the state of emergency proclamation. This does not immediately relate to or change Atherton’s current operations for permit review and construction; however it could come into effect should such an emergency proclamation be issued in the future for San Mateo County. This bill had not yet been signed at the time of the Planning Commission hearing on September 24, 2025, but was subsequently signed by the Governor on October 10, 2025. This bill went into effect immediately due to its emergency response nature.
Senate Bill 543
JADU Definition
This bill revises the definition of a JADU to clarify that the 500 square foot maximum applies specifically to “interior livable space” rather than including non-habitable areas. Staff is proposing to update the JADU definition in Atherton’s ADU ordinance in anticipation of this definition change.
ADU Review Periods
This bill also shortens ADU review periods by requiring jurisdictions to determine whether an application is complete within 15 business days of submittal. Once deemed complete, the application must be approved or denied within 60 days, or else the application is automatically deemed approved.
November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
This bill also had not yet been signed at the time of the Planning Commission hearing on September 24, 2025, and was signed on October 10, 2025. However, this bill will not go into effect until January 1, 2026.
Review Clarity
ADUs above Detached Garages
The Town allows a detached ADU to be constructed above a detached garage and have a total height of up to 25 feet. These units are allowed by the Town to incentivize ADU construction with the intent that the entirety of the structure will adhere to the Town’s local setback requirements for accessory buildings. State-exempt units with reduced 4-foot setbacks are generally not eligible for this provision as they must exceed the state’s maximum height limits to locate above a garage.
However, staff has received inquiries seeking to combine the state and local standards. To address confusion at the counter, staff is proposing language clarifying that to use the increased height, the entire structure needs to meet Atherton accessory building and structure setbacks, inclusive of the garage, ADU, and stairwells.
Attached ADUs
Staff is proposing to add the phrase “structurally abuts” to the attached ADU definition to clarify that the ADU must share a structural wall with the primary dwelling. This addresses situations where applicants have been under the impression that an ADU qualifies as “attached” because it is connected to the primary dwelling by a breezeway, deck, or other structure that extends the building footprint.
Exemptions from Maximum Floor Area Requirements
State law asserts that there is no floor area limitation for the conversion of an existing nonconforming building to an ADU, regardless of that building’s permit history. The current Atherton ADU ordinance contains the phrase “existing legal nonconforming building.” Staff is proposing to remove the word “legal” from the phrase to clarify that the structure is not required to have been permitted initially. Note that this does not preclude the conversion or “legalization” of the unit from complying with health and safety standards and inspection by a Building official.
Additionally, since the Atherton ADU ordinance already specifies that there is no floor area limitation for conversion ADUs on single-family lots, staff is proposing to expand this language to address ADUs on multifamily lots, as the language is not currently in the code. Specifically, there are no floor area limitations for ADUs created through the conversion of non-livable space within multifamily dwellings, or for detached ADUs located on multifamily lots, consistent with state law. Staff is recommending these changes based on feedback provided from HCD during the review of ordinances submitted by other local jurisdictions.
Distinction between Basements and Stories
Atherton allows basements below ADUs, which are regulated under a separate section of the ADU ordinance; no changes are proposed for that section. However, staff recommends adding clarification that basements do not count toward the two-story limit for ADUs.
November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
Entrance Requirements
The language in this section currently requires an exterior entrance facing the interior, side, or rear for attached ADUs, JADUs, and detached ADUs. As referenced earlier, staff is proposing to exempt 66323 units from this requirement, in alignment with state law. However, this requirement will continue to apply to non-exempt units.
Staff is proposing additional amendments to this section to clarify the intent during the 2024 ADU Ordinance update. The current language does not technically mandate that entries only face the interior of the lot; it only requires there be an entrance that complies. Staff has reviewed multiple ADUs designed with more than one entry, including one entry that satisfies this requirement and one entry that faces outward. To align with the intent of this requirement staff is proposing an amendment that clarifies that all entries must face the interior of the lot.
ADU Rental and Ownership
Staff has added language to align with California Government Code Section 66341, which requires jurisdictions to allow the sale of an ADU under certain conditions if the unit or primary dwelling was built or developed by a qualified nonprofit corporation. A reference to the related state code section has been added to this section of the Atherton ordinance. Additionally, per Section 66333(c)(1) of the California Government Code, JADUs may not be sold or otherwise conveyed separately from the primary dwelling. This restriction remains in place for JADUs.
FINDINGS:
Chapter 17.18 of the AMC sets the process for zoning code amendments whereby the Planning Commission adopts a resolution with recommendations to the City Council. The Council will then approve, conditionally approve, or deny the zoning amendments. To approve the amendments the Council must find that the changes are consistent with the Town’s General Plan goals, policies, and implementation programs.
The proposed amendments allow the Town to be compliant with recent changes in state law related to the development of Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) and address the following General Plan Goal, Objective, Policies and Program:
Housing Element Goal 3.720 Use Accessory Dwelling Units to meet a substantial portion of the Town’s moderate to very low-income
housing need.
Housing Element Objective 3.721 A. Realize the construction of 208 new accessory dwelling units planned for occupancy by moderate to
extremely low-income households in Atherton from
2023-2031.
Housing Element Policy 3.722 A. Actively promote the Accessory Dwelling Unit provision of the Atherton Zoning Ordinance by
encouraging and incentivizing homeowners and
November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
developers to include attached or detached Accessory
Dwelling Units in existing or new homes. This will
include educating homeowners on rental alternatives
and the need for ADU reporting.
Housing Element Policy 3.762 B. The Town shall continue to encourage the production and availability of more affordable housing
through the development of new accessory dwelling
units, and private and public-school faculty and student housing.
Housing Element Program 3.812(A) Continue to encourage the development of ADUs and approve ADUs ministerially in conformance with State
Law provisions.
CONCLUSION:
To respond to the current state housing crisis, the State Legislature continues to pass bills designed to encourage the production of both ADUs and JADUs. Cities are expected to update their local ordinances to comply with the state legislation. If the Town fails to bring its local ordinance into conformance, applicants would be permitted to develop under the state legislation. Since the Town actively reviews ADU applications, adopting the local updates will allow the Town to continue to process applications with more clarity and compliance. The adoption of amendments to the ADU Ordinance will also assist the Town in fulfilling its Regional Housing Needs Allocations (RHNA) requirements for the adopted 6th Cycle Housing Element.
FISCAL IMPACT:
The cost associated with the preparation of the draft Ordinance amendments are included within the annual Planning Department budget. The cost to implement the Ordinance will be paid for by the applicants of related development projects.
ENVIRONMENTAL IMPACT:
The project is Categorically Exemption per Section 15305 of the CEQA Guidelines. Section 15305 relates to Minor Alterations in Land Use Limitations, as the ordinance amendments would not result in any changes to land use or density.
PUBLIC NOTICE:
Public notification was achieved by posting the agenda, with this agenda item being listed, at least 72 hours prior to the meeting in print and electronically. Legal advertisement of this hearing was published in The Almanac newspaper. Notice of this hearing was also mailed to all property owners within the Town. Information about the project is also disseminated via the Town’s electronic News Flash and Atherton Online. There are approximately 1,200 subscribers to the Town’s electronic News Flash publications. Subscribers include residents as well as stakeholders November 19, 2025, City Council Staff Report
ADU Ordinance Amendments
– to include, but be not limited to, media outlets, school districts, Menlo Park Fire District, service provides (water, power, and sewer), and regional elected officials.
FORMAL MOTION:
I move that the City Council introduce and conduct the first reading of an ordinance to amend Chapter 17.52 of the Atherton Municipal Code “Accessory Dwelling Units” based on reasons outlined in the Staff Report.
/s/Brittany Bendix
Brittany Bendix, Town Planner
/s/Gerry Martin
Gerry Martin, Assistant Planner
Attachments:
1. Planning Commission Staff Report and Attachments
2. Draft Amendments with changes in red
3. Draft City Council Ordinance
4. Current State Law – Government Code Sections 66310 through 66342
5. SB 543 Legislation Text