ADU Ordinance
Updates
January 26, 2026
Liz Gagliardi, Associate Planner
Community Development Department
CityCity of San Mateo – City of San Mateo – City CouncilCouncil Presentation Overview
•Background
•ADU Ordinance Updates
•Changes to Address HCD Comments for State Law Compliance •Additional Local Changes to Address Community Needs &
Ordinance Functionality
•Recommendations for Adoption
Background
• 2016/2019 – California legislature passed initial state-wide ADU laws to streamline and promote ADU development
• March 2022 – City of San Mateo adopted an updated local ADU Ordinance (SMMC Ch. 27.19)
• October 2024 – HCD provided formal review of the City’s ADU Ordinance • January 2025 – HCD published updated ADU Handbook
• August 2025 – Planning Commission Study Session on Ordinance Updates • September 2025 – Virtual Community Webinar on ADU Ordinance Updates • December 2025 – Planning Commission Public Hearing and Recommendation to City Council to adopt ADU Ordinance Updates Year Total Permits Issued Permits Finaled
2022* 61 57
2023 89 72
2024 66 33
2025* 85 2
TOTAL 301 164
*Data from March 21, 2022 – December 3, 2025
Background – ADU Permitting Data
Housing Element Policy H1.4
Support Increased ADU Development.
Implementation Action H1.4 (a)
Amend the City’s ADU Ordinance to align with current State law and to resolve any inconsistencies identified by HCD Housing Element Context
ADU Ordinance Updates
Changes to Address HCD Comments for State Law Compliance Additional Local Changes to Address Community Needs &
Ordinance Functionality
ADU Ordinance Updates
Changes to Address HCD Comments for State Law Compliance Additional Local Changes to Address Community Needs &
Ordinance Functionality
ADU Ordinance
Updates
• Updates to Definitions
• Clarification for ADU Separate Sale
• Fee Clarification
• Removal of Variance Process
• Number of ADUs permitted with Single-Family
• Front Setback Clarification
• Clarification of Architectural Standards &
Removal of Subjective Standards
• JADU Updates
• Multifamily ADU Updates
HCD Review & State Law Compliance
ADU Ordinance Updates
Changes to Address HCD Comments for State Law Compliance Additional Local Changes to Address Community Needs &
Ordinance Functionality
Additional Local
Standards
Setback Exemption
Maximum ADU Size
Height Limit for Detached ADUs
Parking Exemption for ADUs & Voluntary Parking Standards Second Story Decks & Balconies
Updates to ADU Discretionary Review (ADUDR)
ADU Discretionary Review
State Law Context
Ministerial approval is required when an ADU meets State law requirements A local agency may apply objective standards on ADUs
Local Context - Two paths for ADU review:
1) Ministerial Review – for ADUs that meet development
standards of the Ordinance
2) Accessory Dwelling Unit Discretionary Review (ADUDR) – alternative option for any ADU that does not meet the
development standards of the ADU Ordinance
ADUDR Updates
Clarification on ADUDR Applicability
• Exceptions to ADU setbacks, height, or daylight
plane. No exceptions to increase FAR
Updated ADUDR Findings
Updated ADUDR Appeal Process
• May be appealed to City Manager or designee
(could be a hearing officer)
Maximum ADU Size
State Law Context
ADUs of at least 800 square feet with 4-foot setbacks are allowed by-right Must allow ADUs of at least:
• 850 square feet for studio and one-bedroom ADUs
• 1,000 square feet for ADU with more than one bedroom
Local Context – No specific maximum size.
• ADU size is regulated by Floor Area Ratio (FAR). Up to 800 square feet of ADU area is exempt from total FAR
• ADU cannot be larger than primary unit
Height Limit for Detached ADUs
State Law Context
• Must allow detached ADUs up to 16 feet, or up to 18 feet (plus two feet to allow for matching roof pitch to existing dwelling) for detached ADUs near transit or on multistory multifamily lots • Must allow two-story detached ADUs
• State law only regulates total height (not plate vs. roof peak)
Local Context
Current Standard – 16 feet to top
wall plate and 24 feet to roof peak
Updated Standard – 18 feet to top
wall plate and 24 feet to roof peak
All measured from existing grade
Height Limit for Detached ADUs
Setback Exemption
Current Standard
4-foot side and rear setbacks required for all ADUs.
Allows for conversion of existing structures within
setbacks.
Updated Standard
Allow ADUs in the rear one-third of a parcel to be built within side and rear setbacks if they meet existing
requirements for Accessory Structures in the rear one-
third of a parcel
State Law Context
• When parking is required for an ADU, may not exceed one space per unit or per bedroom, whichever is less.
• No parking required when parking is demolished or converted to an ADU • No parking required for ADUs:
• Within 1/2 mile walking distance of public transit
• Within an architecturally and historically significant historic district • That are part of the proposed or existing primary residence or an accessory structure • When on-street parking permits are required but not offered to the occupant of the ADU • When there is a car share vehicle located within one block of the ADU • When a permit application for an ADU is submitted with a permit application to create a new single-family dwelling or a new multifamily dwelling on the same lot, provided that the ADU or the parcel satisfies any other criteria listed above.
Parking Exemptions for ADUs
Parking Exemptions for ADUs
• Vast majority of residential
properties in San Mateo
exempt from ADU parking
requirements.
• Red circles show properties
that are more than a ½ mile
from a transit stop.
Parking Exemptions for ADUs
Current Standard
Minimum of one standard-sized off-street parking space for each ADU is required.
• ADU parking can be covered or uncovered, may be in tandem configuration.
• Exemptions to providing off-street parking are also provided pursuant to State law
Updated Standard
Eliminate all required off-street parking for ADUs citywide.
Voluntary Parking for ADUs
Updated Standards:
• Up to two voluntary parking spaces may be
provided for an ADU
• Tandem orientations allowed for ADU parking
• Existing driveway/curb cut may remain when
garage is demo’d or converted to an ADU
• Driveways can be expanded to up to 20-ft
width for extra parking area
• Setback exemptions for covered parking
within the footprint of a two-story ADU
Second Story Decks and Balconies
Current Standard
All second-story decks & balconies
require ADUDR.
Second Story Decks and Balconies
Updated Standard
Second-story decks & balconies considered ministerially when:
• No portion of the deck or balcony is within side/rear setback of the underlying zoning district.
• Deck or balcony does not exceed 50 square feet
• Deck is interior-facing
ADUDR process remains available for decks/balconies that do not meet above standards*
*Roof decks are prohibited
Summary of December 9, 2025 Planning
Commission Public Hearing
•One written comment was submitted, no public speakers provided verbal comment at the meeting
•Planning Commission asked some clarifying questions to staff and discussed the updates, identifying three additional changes that the Commission voted to include in the recommendation to City Council. •The motion to recommend approval with the three additional changes was carried, with 4 commissioners voting in favor, none opposed, and one commissioner absent.
Summary of Planning Commission Recommendations
1) Add language to Section 27.19.045 to clarify 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. 2) Keep existing appeals process in Section 27.19.045 for ADUDR applications to be appealed to Planning Commission, and if appealed again to City Council. 3) 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 balcony “shall not face adjacent residential properties”.
Next Steps
Staff will partner with the ADU Resource Center of San
Mateo County on continued public outreach and
information sessions to support local ADU production
Ordinance will become effective 30 days after adoption
Staff will update ADU Webpage, Handouts & Supplemental
Materials
Ordinance will be brought back to Council for a second
reading and adoption.
Introduce an Ordinance to amend San Mateo Municipal Code Chapter 27.19, "Accessory Dwelling Units and Junior Accessory Dwelling Units – 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 27080.17 of the Public Resources Code and Section 15282(h) of the CEQA Guidelines.
Recommendation
Thank You
Liz Gagliardi
Associate Planner, Community Development
[email protected]