The height limit recommendation in the staff report aligns with what the planning commission recommended three years ago. What should now be addressed is that in certain areas of the city first floor heights are raised above existing grade by three feet to alleviate sea level rise and high ground water incursion. This increased ground floor height needs to be adjusted to the allowable heights of ADU's in the parts of the city afflicted by these hazards.
The proposed maximum size of 1,200 square feet for an ADU conflicts with guidance by planning commission and council during the last ordinance update which set the size limitations by the Floor Area Ratio, FAR. The staff report alludes to a city guideline that an ADU cannot be larger than the primary residence, that is totally contrary to prior staff directions. The size of an ADU should be predicated by FAR and not an arbitrary preference of neighborhood balance and any existing codes should be abandoned.
The staff report states that over the last three years an average of 77 ADU’s have been built yet per the city’s Annual Progress Reports for those years a total of 181 ADU’s have been completed, which is an average of 60 per year. The cities RHNA cycle 6 has a goal of building 7,015 housing units between 2023 – 2031. Unfortunately, only 291 units have been built and of those 44% are ADU’s.
Another issue of note is per state law ADU permits need to be approved in two months. In San Mateo County ten of the cities average between 0 and 2 months to issue permits. The city of San Mateo averages between four and eight months to issue a permit. This is two to four times the state mandated timeline to just get a permit and by far the worst performing city in the county on this critical aspect.
The percentage of new housing built in California represented by ADU’s is 22%, yet in San Mateo that percentage is 44%. With our ongoing struggles to build housing it has become more important to make the process of building ADU’s as streamlined and efficient as possible. You as a commission can implement guidelines that will help the public in its desires to build housing in their own backyards that are used for a wide variety of housing needs.
Thank you
John Ebneter
Ref: PC meeting on 8/26/24
8/26/25 City of San Mateo Planning Commission
Item number two
regulate them by FAR. In practice, this has blocked projects that Council intended to support. For example, a North Central proposed duplex ADU project was denied because staff required the ADU to be smaller than the smaller of the two duplex units, even though the duplex was a similar size as the ADU. This is particularly inequitable in older neighborhoods where many homes are under 1,200 sq. ft.
Residents in Baywood or San Mateo Park with 3,000+ sq. ft. homes can easily build large ADUs, while families in North Central and Central are effectively capped at much smaller sizes. This undermines Affirmatively Furthering Fair Housing Law by blocking working families from opportunities to create family-sized ADUs.
These fixes will rectify the policy to align implementation with the Council’s original vision, allowing homeowners to reinvest in their properties without unnecessary expense or delay and create space for more affordable and “missing middle” homes, while advancing San Mateo’s climate resilience and equity goals.
As you deliberate on the ADU Ordinance Updates, the inclusion reforms that reduce bureaucracy, save money for homeowners, preserve neighborhood livability, and align City policy with State law and the Council’s original intent should be a top priority.
Amourence Lee
Former Mayor
City of San Mateo
Definition of “Primary Residential Dwelling Unit”: The municipal code defines a “primary residential dwelling unit” as the largest dwelling on a lot, which effectively requires that all ADUs be smaller than the existing home. This conflicts with the Council’s prior decision to remove size caps on ADUs and instead set of zoning rules. This can make it nearly impossible to design functional ADUs above garages and directly contradicts Council’s intent.
Dec 9, 2025
City of San Mateo
330 West 20th Avenue
San Mateo, CA 94403
By Email: [email protected]
CC: [email protected]; [email protected]; [email protected]; [email protected]
Re: Proposed Amendments to the City’s ADU Regulations
Dear San Mateo Planning Commission,
The California Housing Defense Fund (“CalHDF”) submits this letter as a public comment concerning Item 2 on the agenda for the December 9, 2025 Planning Commission meeting, a study session for an update to the City’s regulations for the development of accessory dwelling units (“ADUs”) and junior accessory dwelling units (“JADUs”).
CalHDF applauds the City for updating its ADU regulations to keep pace with changes in state law. CalHDF writes to
flag specific legal issues with the ordinance, which the City should address before passing the ordinance.
Background
The law gives local governments authority to enact zoning ordinances that implement a variety of development standards on ADUs. (Gov. Code, § 66314.) The standards in these local ordinances are limited by state law so as not to overly restrict ADU development. (See id.) Separately from local ADU ordinances, Government Code section 66323 establishes a narrower set of ADU types that local governments have a ministerial duty to approve. “Notwithstanding Sections 66314 to 66322 ... a local agency shall ministerially approve” these types of ADUs. (Id. at subd. (a).) This means that ADUs that satisfy the minimal requirements of section 66323 must be approved regardless of any contrary provisions of the local ADU ordinance. (Ibid.) Local governments may not impose their own standards on such ADUs. (Gov. Code, § 66323, subd. (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).”].)
2201 Broadway, PH1, Oakland, CA 94612
[email protected]
In addition, ADUs that qualify for the protections of Government Code section 66323, like other ADUs, must be processed by local governments within 60 days of a complete permit application submittal. (Gov. Code, § 66317, subd. (a).)
State law also prohibits creating regulations on ADU development not explicitly allowed by state law. Government Code Section 66315 states, “No additional standards, other than those provided in Section 66314, shall be used or imposed, including an owner-occupant requirement, except that a local agency may require that the property may be used for rentals of terms 30 days or longer.”
Impermissible Size Limits on Exemption ADUs on Multifamily Parcels
Code section 27.19.070(c) generally restricts detached ADUs on multifamily parcels to 800 square feet in size. The code does this by only allowing floor area ratio waivers for ADUs up to 800 square feet in size and also only allowing ADUs to be as large as the smallest existing unit on the property, unless the smallest unit is less than 800 square feet, in which case the ADU may be 800 square feet in size.
However, the City should be aware that such size restrictions are not permitted for new construction, detached ADUs on multifamily parcels. Government Code section 66323 subdivision (a)(4) allows up to eight detached ADUs on multifamily parcels without size restrictions. Size restrictions are plainly forbidden by Government Code, section 66323, subdivision (b), which explicitly exempts statewide exemption ADUs from all local standards:
“(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).” Because Government Code section 66323 subdivision (a)(4) does not contain a size limit for new construction, detached ADUs on multifamily parcels, the City may not unilaterally impose one.
HCD reaffirms this requirement of state law on page 20 of the January 2025 HCD ADU Handbook (emphasis added):
A local agency may not impose development or design standards, including both local standards and standards found in State ADU Law, on 66323 Units that are not specifically listed in Government Code section 66323. (Gov. Code, § 66323, subds. (a), (b).) This includes, but is not limited to, parking, height, setbacks, or other zoning provisions (e.g., lot size, open space,
floor area ratio, etc.).
The City must exempt ADUs developed pursuant to Government Code section 66323, subdivision (a)(4) from all size restrictions.
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Parking
Staff is recommending exempting all ADUs from offstreet parking requirements citywide.
CalHDF strongly supports this recommendation. This will encourage ADU development and will help the City meet its RHNA targets.
However, regardless of what the City decides to do in terms of parking requirements, the City should be aware that it cannot require parking for ADUs that conform to the requirements of Government Code section 66323, subdivision (a), as section 66323, subdivision (b) specifically exempts such ADUs from all local requirements.
From page 20 of the January 2025 HCD ADU Handbook (emphasis added):
A local agency may not impose development or design standards, including both local standards and standards found in State ADU Law, on 66323 Units that are not specifically listed in Government Code section 66323. (Gov. Code, § 66323, subds. (a), (b).) This includes, but is not limited to, parking, height, setbacks, or other zoning provisions (e.g., lot size, open space,
floor area ratio, etc.).
In its update to its ADU regulations, the City must exempt section 66323 ADUs from all parking requirements, as is required by state law.
Impermissible Discretionary Process
City Code section 27.19.045 contains a discretionary approval process for ADUs that do not meet code requirements. Such a process is forbidden by state law.
Government Code section 66317, subdivision (a) forbids all discretionary review for ADU approvals: “A permit application for an accessory dwelling unit or a junior accessory dwelling unit shall be considered and approved ministerially without discretionary review or a hearing, notwithstanding Section 65901 or 65906 or any local ordinance regulating the issuance of variances or special use permits.”
The City must therefore eliminate any discretionary review of ADUs.
Additionally, the findings contained in City Code section 27.19.045 include non-objective findings:
(2) The proposed ADU would not result in a negative impact to public health, safety, or welfare.
(3) If the proposed ADU does not comply with height, setback, or daylight plane standards, there are exceptional circumstances applicable to the property that would
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