Bay Area ADU Ordinance Compliance: What Owners Should Know

Bay Area ADU Ordinance Compliance: What Owners Should Know in 2026

The California Department of Housing and Community Development (HCD) has told San Jose, Los Altos, Mountain View and Hayward that their accessory dwelling unit (ADU) ordinances appear outdated and may not comply with current state law. Under Government Code section 66316, a noncompliant local ADU ordinance is legally void, so the city must apply state ADU standards directly to permit applications until it adopts a replacement. For owners of a fourplex, a sixplex or a larger apartment property in one of these cities, that shift can mean more buildable ADU capacity than the ordinance posted on the city's own planning page currently shows.

Key takeaways

HCD has sent letters since October 2025 to San Jose, Los Altos, Mountain View and Hayward stating that each city's ADU ordinance may be outdated and out of compliance with state law.
Under Government Code section 66316, a noncompliant local ordinance is "null and void." Until a city adopts a compliant replacement, state ADU law governs applications directly, often a more permissive standard than the outdated local one.
SB 1211, effective January 1, 2025, raised the number of detached ADUs allowed on a lot with an existing multifamily building from two to eight.
Mountain View received two separate HCD letters in 2026, a sign the review is active and ongoing rather than a single notice.
None of this waives local building and safety review. It changes which rulebook, city or state, currently governs how many ADUs an owner can add and on what terms.

Why HCD is telling cities their ADU ordinances don't count

An accessory dwelling unit, often called a granny flat or in-law unit, is a secondary, independent living space built on a residential or multifamily lot. The legislature has amended state ADU law almost every year since 2019, and HCD runs an ongoing review of local ordinances against the current version of that law. When HCD's records show a city hasn't updated its ordinance to match, it sends a letter of technical assistance asking the city to either demonstrate that its existing rules still comply or commit to a timeline for fixing them.

Government Code section 66316 gives that request legal weight. A local ADU ordinance that conflicts with state law is null and void, meaning state standards, not the version posted on the city's website, govern permit decisions until the city catches up. HCD recommends that cities in this position repeal the outdated ordinance outright, so applicants aren't left guessing which rulebook applies.

Which South Bay, Peninsula and Alameda County cities have been flagged

Four cities across the three regions this blog covers have received letters in the current review cycle:

San Jose's most recent ADU ordinance on file with HCD dates to 2021. HCD's letter, sent December 10, 2025, asked for a response by January 9, 2026. Los Altos's ordinance on file dates to 2020; its letter arrived December 5, 2025, with a response due January 4, 2026. Hayward's ordinance on file dates to 2017, the oldest of the four; its letter arrived October 8, 2025, with a response due November 7, 2025.

Mountain View is the more involved case. A May 11, 2026 letter referenced a 2023 ordinance and requested a response by June 10, 2026. A second letter, dated May 28, 2026, addressed Ordinance No. 02.2024, which the city adopted January 23, 2024. That letter noted the city's own stated plan: follow state ADU law directly in the interim and adopt a new compliant ordinance by the end of 2026. HCD responded that this interim approach doesn't satisfy Government Code section 66326(b), and again recommended repealing the outdated ordinance.

None of the four letters identifies a specific defective provision. Each asks the city to show its work or commit to fixing it, and HCD's publicly posted letters don't yet show a follow-up confirming any of the four adopted a new ordinance. Owners in these cities should confirm current status directly with the planning department rather than assume either the old local ordinance or the state default still applies by default.

What SB 1211 changed for owners of 2-to-20 unit properties

Separate from the compliance letters, state law itself got more generous for multifamily owners. SB 1211, effective January 1, 2025, raised the cap on detached ADUs allowed on a lot with an existing multifamily building from two to eight. The law also bars a city from requiring replacement parking when an owner removes uncovered parking to make room for an ADU, and it limits local agencies to the development standards set out in Government Code section 66323 rather than layering on additional restrictions of their own.

For an owner of a fourplex or a modest six-unit building with room on the lot, that is four times the detached-ADU capacity the old two-unit cap allowed. A separate 2025 law also expanded amnesty for unpermitted ADUs and junior ADUs built before January 1, 2020, giving owners holding an older unpermitted unit a clearer path to bring it into compliance without triggering building-code penalties for the original construction.

What this means if you own property in a flagged city

Before filing an ADU application in San Jose, Los Altos, Mountain View or Hayward, ask the planning department in writing which standard currently governs review: the city's own ordinance, or the state's default standards. Noncompliant local ordinances tend to be more restrictive than the state floor, since that gap is usually what triggers an HCD letter in the first place. Owners may currently have more by-right ADU capacity than the posted local code implies.

Get the applicable standard confirmed in writing before committing to architectural plans, rather than assuming anything informally or skipping permitting. An added ADU is immediate rental upside on a property you already own, and for an owner weighing a refinance or a 1031 exchange, that operational upside can change the math on whether to hold, improve or sell.

Region snapshot: South Bay, Peninsula and Alameda County

In the South Bay, San Jose is the flagged example on record, but each Santa Clara County city sets its own ordinance. Owners in Santa Clara, Sunnyvale, Campbell or Milpitas should check their city's ordinance date individually rather than assume San Jose's situation applies countywide.

On the Peninsula, both Los Altos and Mountain View have been flagged, which suggests San Mateo County and southern Santa Clara County cities are getting real scrutiny in this review cycle. Owners in Redwood City, San Mateo, Burlingame or elsewhere in San Mateo County should confirm their own city's status rather than assume it mirrors Los Altos or Mountain View.

In Alameda County, Hayward's 2017 ordinance is the flagged example. Oakland, Berkeley, Fremont and other Alameda County cities hadn't appeared in HCD's public letters as of this writing, but HCD's review appears to move city by city rather than county-wide, so an owner anywhere in the county should still confirm their city's ordinance reflects 2025 law before relying on it.

This post is for general information and doesn't constitute legal, tax or financial advice about your specific property. Confirm which ADU rules currently apply to your parcel with your city's planning department, and talk to a land-use attorney before relying on state default standards in place of a local ordinance.

The R&Z Group works with South Bay, Peninsula and Alameda County owners weighing whether added ADU capacity changes the math on holding, refinancing or selling a property. [Internal link: Request a property valuation] is a good place to start that conversation, and [Internal link: South Bay and Alameda County multifamily listings page] has current inventory for owners exploring a sale instead.

Frequently asked questions

Is my city's ADU ordinance still enforceable in 2026?

It depends on whether the city updated it to match current state ADU law. HCD has publicly flagged San Jose, Los Altos, Mountain View and Hayward ordinances as potentially outdated as of mid-2026. If a city's ordinance is noncompliant, Government Code section 66316 treats it as null and void, meaning state standards govern until the city adopts a fix.

How many ADUs can I build on a multifamily lot in California now?

Up to eight detached ADUs are allowed on a lot with an existing multifamily building under SB 1211, effective January 1, 2025, up from the previous cap of two. Local size, parking and other development standards still apply within the limits Government Code section 66323 sets.

What happens if HCD finds a city's ADU ordinance noncompliant?

The city must either show HCD how its existing ordinance already complies with current law or commit to a timeline for repealing or amending it. In the meantime, HCD directs the city to apply state default ADU standards directly to permit applications rather than the outdated local rules.

Does this change parking or owner-occupancy requirements for my ADU?

It can. Recent state law bars replacement parking requirements when uncovered parking is removed for an ADU, and a 2023 law ended owner-occupancy requirements for standard ADUs, though junior ADUs still carry occupancy rules tied to shared sanitation. Confirm which version, city or state, currently applies to your parcel before assuming either set of rules.

Should I wait to apply for an ADU permit until my city updates its ordinance?

Not necessarily. Since the state default standards HCD is directing noncompliant cities to use tend to be more permissive than the outdated local ordinance, waiting could mean building under a more restrictive rule once the city catches up. Ask the planning department in writing which standard currently governs before commissioning plans.

Bay Area ADU Ordinance Compliance: What Owners Should Know