SB 9 & 10

Senate Bill (SB) 9

On September 16, 2021, the Governor signed Senate Bill 9, Atkins (SB9), which will take effect in all local jurisdictions on January 1, 2022.

What Does SB 9 Do?

SB 9 allows all properties within a “single-family residential zone” to be subdivided into two parcels and developed with two primary dwelling units per lot, irrespective of local standards. In essence, the law allows for two new types of development activities that must be reviewed ministerially without any discretionary action or public input.

  • A Two-Unit Project allows the development of two primary dwelling units or, if there is already a primary dwelling unit on the lot, the development of a second primary dwelling unit on a legally subdivided lot.
  • Urban Lot Splits or SB 9 Lot Splits allow for the subdivision of an existing legally subdivided lot into two lots regardless of the Town’s normal minimum lot size.

Generally, SB 9 will result in the potential creation of four dwelling units from an existing single-family parcel. In comparison, a single-family property is currently permitted three units: a single-family dwelling, an ADU, and a JADU.

Does the Project Qualify?

To qualify for ministerial approval under SB 9, the project must satisfy a number of qualifying criteria including, but not limited to the following:


Lot Location

  • Single-family lot zoning designation;
  • Not a historic property or within a historic district or land identified for conservation;
  • Not within a high fire severity zone unless all dwellings on the site comply with current fire code requirements for dwellings in a very high fire hazard severity zone;
  • Not within an environmentally sensitive area, a hazardous site, within a delineated earthquake fault zone, or within a 100-year flood zone;
  • Not established through a prior urban lot split; or
  • Not adjacent to any lot that was established through a prior urban lot split by the owner of the lot to be split or by any person acting in concert with the owner. 


Lot Size:

  • The lot to be split must be at least 2,400 square feet;
  • The resulting lots must each be at least 1,200 square feet; and
  • The resulting lots must each be between 60% and 40% of the original lot area.

Unit Size:

  • Each unit must be less than or equal to 800 square feet


Each lot must adjoin the public right-of-way and have frontage on the public right of way of at least 50 feet.

Lot Coverage and Setbacks

Lot Coverage:

  • 50% Maximum lot coverage allowed for total combined hardscape + structural


  • Side/Rear setbacks of 20-feet (except as necessary to allow two units at 800 sq. ft. each; but no less than 4 feet)
  • Front setback of 30 feet


Each new primary dwelling unit must have at least one off-street parking space. unless exempt. No parking is required for projects that lie within a half-mile walking distance of a high-quality transit corridor or a major transit stop


  • Existing legal primary dwelling: Any new primary dwelling unit must match the existing primary dwelling unit in exterior materials, color, and dominant roof pitch. 
  • No existing: If two new primary dwellings are developed on the lot - the dwellings must match each other in exterior materials, color, and dominant roof pitch. 


Limitations on tree removal and required landscaping screening

Use and Deed Restriction


  • Residential-only. The rental of any unit created must be for a term longer than 30 days (no short-term rentals allowed).

Deed Restriction:

  • A deed restriction is required, specifying no short-term rental, no non-residential use, no separate conveyance; and that development is limited to SB 9 projects.


Project would not alter or demolish:

  • Any housing that is income-restricted for households of moderate, low, or very low income
  • Any housing that has been occupied by a rental tenant in the last three years 


Owner Occupancy

The applicant must sign an affidavit stating that the applicant intends to occupy one of the dwelling units on one of the resulting lots as the applicant's principal residence for a minimum of three years after the urban lot split is approved.

Separate Conveyance Within a Lot:

  • Primary dwelling units on the lot may not be owned or conveyed separately from each other; no condos, no timeshares or separate-use co-ownerships are allowed.


Owner Occupancy

Individual property owners must occupy one of the dwellings on the lot as the owners’ legal principal residence.

Information contained in this summary is for general education and knowledge, but is not designed to be, and should not be used as, legal advice. Nor is it binding on the Town.

What Can the Town Do?

SB 9 is imposed by the State and there is no way for the Town to “opt-out” of the law. Local agencies may impose standards, but only objective zoning standards, objective subdivision standards and objective design standards. The Town may not impose any standard(s) that would:

  • Physically preclude the construction of two units of less than 800 square feet each per property;
  • Require larger minimum lot size than what is set forth in the statute; or
  • Requiring onsite parking spaces for properties one-half mile walking distance of either a high-quality transit corridor or a major transit stop, or within one block of a car share vehicle.

What Is the Town Doing?

On December 13, 2021, the Town adopted an urgency ordinance amending the Hillsborough Municipal Code to impose objective development standards based on existing residential standards for building size, lot coverage, setbacks, and building heights (unless conflicting with SB9 mandated standards). The intention is to adopt basic standards prior to the SB 9 legislation taking effect on January 1, 2022.

What Are the Next Steps?

Beginning Spring 2022, the Town will proceed with the Housing Element Update process with substantial community engagement. As part of this effort, the Town will refine its SB 9 standards. This might involve additional or updated detailed objective design standards.

Senate Bill (SB) 10

California Senate Bill (SB) 10 allows (but does not require) local agencies to adopt an ordinance to allow up to 10 dwelling units on a parcel if the parcel is within a transit-rich area or urban infill site. The Town currently has no plan to adopt such an ordinance.