Town of Atherton
ADU Ordinance Update
City Council
November 19, 2025
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.
2 Background
Major
overhaul
of ADU
legislation
by State
2019
Town
updates
ADU
Ordinance
2020
Ongoing
changes to
State law
2020 -
2023
Town
updates to
align with
State law
2024
3 Areas of Change
4 Sections changed in Atherton ADU ordinance
• Definitions
• Maximum Number of Units
• Floor Area Requirements
• Exemptions from Maximum Floor Area Requirements
• Setback Requirements
• Entrance Requirements
• Height
• Heritage Trees
• Privacy, Screening and Landscaping
• Lighting Restrictions
• ADU Rental
• Passageways and Internal Connections
• Certificate of Occupancies
• Application Review
State Laws:
• SB 477 (2024)
• SB 1211 (2024)
• AB 1332 (2024)
• AB 2553 (2024)
• AB 462 (2025)
• SB 543 (2025)
SB 477
5 Bill:
Renumbering of ADU and JADU Government Code Sections:
65852.150, 65852.2, 65852.22, 65852.23, 65852.26
66310-66342
Changes to Atherton Code: All sections referencing state law are updated to reflect the new numbering SB 1211
6 Added State Language:
Changes to Atherton Code: These types of ADUs are now
exempted from Atherton’s:
California Government Code 66323(b)
A local agency shall not impose any objective
development or design standard that is not authorized by this section upon any accessory dwelling unit that meets the requirements of any of paragraphs (1) to (4),
inclusive, of subdivision (a).
(66323/state-exempt units)
66323/State-exempt 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 multifamily units, whichever is less, are allowed. On a lot with a proposed multifamily dwelling, no more than 2 detached ADUs are allowed.
• Entrance Requirements
• Heritage Tree Ordinance (most already exempted)
• Privacy, Screening, and Landscape Requirements
• Exterior Lighting Requirements
• Internal Connection Requirements
SB 1211 cont.
7 California Government Code 65852.2(e)
(D) (i) Not more than two accessory dwelling units that are located on a lot that has an existing or proposed
multifamily dwelling, but are detached from that
multifamily dwelling…
State Law (previously): State Law (now):
Changes to Atherton Code: Number of allowed detached
ADUs on lots with an existing multifamily dwelling
updated to reflect state law
California Government Code 66323(a)(4)
(ii) On a lot with an existing multifamily dwelling, not more than eight detached accessory dwelling units.
However, the number of accessory dwelling units
allowable pursuant to this clause shall not exceed the
number of existing units on the lot.
(iii) On a lot with a proposed multifamily dwelling, not more than two detached accessory dwelling units.
Old: 2 allowed
New: 8 allowed, but not more than existing
units on the lot
AB 1332
8 Changes to Atherton Code: Language added to reflect the 30 day approval timeline for applications that use preapproved ADU plans
Bill:
• Requires local preapproval program for ADU plans
• Gives permitting agencies instructions on how the program is to be operated • Mandates that permitting agencies make a decision on a completed ADU application using preapproved plans within 30 days
AB 2553
9 Public Resource Code 21064.3
“Major transit stop” means a site containing any of the following:
(a) An existing rail or bus rapid transit station.
(b) A ferry terminal served by either a bus or rail transit service.
(c) The intersection of two or more major bus routes
with a frequency of service interval of 15 minutes or
less during the morning and afternoon peak commute
periods.
State Law (previously): State Law (now):
Changes to Atherton Code: “Major Transit Stop” definition updated to reflect state law, as well as existing state language not currently included in the definition
Public Resource Code 21064.3
“Major transit stop” means a site containing any of the following:
(a) An existing rail or bus rapid transit station.
(b) A ferry terminal served by either a bus or rail transit service.
(c) The intersection of two or more major bus routes
with a frequency of service interval of 20 minutes or
less during the morning and afternoon peak commute
periods.
AB 462
10 Changes to Atherton Code: New language added to the code to account for an exception in this specific circumstance California Government Code 66328:
(a) A local agency shall not issue a certificate of occupancy for an accessory dwelling unit before the local agency issues a certificate of occupancy for the primary dwelling. (b) Notwithstanding subdivision (a), a local agency shall issue a certificate of occupancy for an accessory dwelling unit constructed in a county that is subject to a proclamation of a state of emergency made by the Governor on or after February 1, 2025, if both of the following requirements are met, even if the primary dwelling has not yet been issued a certificate of occupancy:
(1) The primary dwelling was substantially damaged or destroyed by an event referenced in the state of emergency proclamation issued by the Governor.
(2) The accessory dwelling unit has been issued construction permits and has passed all required inspections.
(c) Subdivision (b) does not apply to an accessory dwelling unit attached to the primary dwelling.
State Law:
SB 543 (in effect 2026)
11 California Government Code 66313
(d)”Junior accessory dwelling unit” means a unit that is no more than 500 square feet in size and contained
entirely within a single-family residence. A junior
accessory dwelling unit may include separate sanitation facilities, or may share sanitation facilities with the existing structure.
State Law (now): State Law (as of January 1, 2026):
Changes to Atherton Code: “Junior Accessory Dwelling Unit” definition updated and “Livable Space” definition added to reflect anticipated state law
California Government Code 66313
(d)”Junior accessory dwelling unit” means a unit that is no more than 500 square feet of interior livable space in size and contained entirely within a single-family
residence. A junior accessory dwelling unit may include separate sanitation facilities, or may share sanitation facilities with the existing structure.
SB 543 cont.
12 New State Law for California Government Code 666317(ADUs) and 66335(JADUs) :
Changes to Atherton Code: New language added to code to reflect new and existing state law, changing out “permitting agency” for “the Town”
• Permitting agency must provide a comment letter to determine application completeness within 15 business days
• Gives permitting agencies instructions on completeness letter process • If a timely determination is not made, the application is deemed complete • (Already existing) A permitting agency must make a determination on a completed application within 60 days, or else the application is automatically deemed approved.
Review Clarity
13 ADU above Detached
Garage
• Entire structure
needs to meet
Atherton accessory
structure setbacks if
using increased
height (up to 25 ft)
• Clarify that this is
not a 66323 ADU
Attached ADUs
• Add “structurally
abuts” to primary
residence in
definition to clarify
that an attached
ADU must be
structurally
connected to the
primary residence
Floor Area
Exemptions
• Clarify that there is
no floor area
limitation on ADU
conversions of
existing
nonconforming
buildings, not just
legal nonconforming
buildings, per
existing state law
• Add existing state
language that there
is no floor area limit
on multifamily ADUs
Review Clarity cont.
14 Basement/Stories
• Clarify that
basements do not
count toward the 2-
story limit for ADUs
(Note: Basements
already allowed
below ADUs in
Atherton code)
Entrance
Requirements
• Require that all
entries face interior
of the lot for non66323 ADUs
• Clean up intent of
existing language
regarding entrance
requirements in
Atherton code
ADU Rental &
Ownership
• Include existing state
language, that a sale
of an ADU (not
JADU) must be
allowed when
developed by
qualified nonprofits
under specific
conditions
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.
15 Thank you
16