Research
An Overview of Senate Bill 9 (SB-9)
What SB-9's "lot splits" mean for homeowners in California
Senate Bill 9 (SB-9) is a California state law that enables homeowners to split their single-family residential lots into two separate lots and build up to two new housing units on each. SB-9 builds on prior state legislation that has successfully expedited the permitting and construction of accessory dwelling units (ADUs) and junior ADUs (JADUs).
If you live in California, you’ve likely heard about “lot splits” and SB-9. Here’s a quick recap of what those are and what they mean for homeowners in California.
What is SB-9?
California Senate Bill 9, or the California Housing Opportunity and More Efficiency (“HOME”) Act, took effect in January 2022. The sole purpose of the so-called “duplex bill” is to maximize housing potential on single-family residential lots through two provisions:
- Two-Unit Development, which enables homeowners to build two housing units on their lot even if it is only zoned for one unit
- Lot Splits, which allow a lot to be split into two separate parcels
These provisions simplify and expedite the municipal application process, offering an objective, non-discretionary path for homeowners looking to build additional homes on their property. All California cities must comply.
Why does this matter?
California is facing a housing shortage, and single-family zoning is one of the greatest barriers to boosting housing construction. Single-family zoning, which allows only one house per lot, predominates in California - nearly 75% of all developable land in the state is zoned single-family.
Single-family zoning severely limits the types of housing that can be built. It excludes housing types like duplexes and accessory dwelling units (ADUs) that offer benefits to renters and homeowners. These smaller housing types are not only more affordable than most single-family homes but are also better suited for households that would like to live multignerationally, downsize from larger homes, or earn rental revenue from underdeveloped land.
SB-9 is designed to increase housing stock in single-family residential zones by making housing development more straightforward and accessible for homeowners.
What can you build with SB-9?
SB-9 allows qualifying property owners to have two dwelling units per lot. It also allows property owners to split their lots in two, creating the opportunity for up to 4 dwelling units across two lots.
The dwelling units do not need to be attached, leaving a lot of flexibility in how the new homes are configured. Regulations vary by jurisdiction, but potential options include:
- Two single-family dwellings
- Duplex
- House + attached or detached accessory dwelling unit (ADU)
- House + junior ADU (JADU)
What’s the fine print?
To pursue lots splits or development under SB-9, properties must meet a handful of requirements:
- Occupancy. Homeowners who split their lot must commit to living on one of the lots as their primary residence for a minimum of three years.
- Location. To be eligible, properties must be located within an urban area and be zoned single-family residential. Properties located in historic zones, farmland, or environmentally protected areas are not eligible.
- Lot sizes. Lots must be at least 2,400 square feet, as the minimum allowed lot size after splitting is 1,200 square feet. Lots must be split fairly evenly at a ratio no greater than 60:40.
- Demolitions. Because the goal of SB-9 is to create more housing rather than remove existing housing, proposed SB-9 projects cannot require the demolition of any existing rental units that have been leased within the past three years.
- Evictions. Properties with a record of tenant eviction within the last 15 years are not eligible for development under SB-9.
What are some of the drawbacks and benefits?
SB-9 presents a handful of challenges that aren’t unique to the “duplex bill” itself but are worth considering nonetheless.
- Permitting. SB-9 aims to streamline permitting processes, but getting permits approved for any housing development can still be challenging. Jurisdictions can interpret SB-9 in their own ways, and some may still be establishing their new SB-9 application processes. This opens up room for permit delays, which can mean lengthy pre-development timelines before construction can begin.
- Cost. SB-9 projects might be expensive. Extra expenses like impact fees, parcel remapping fees, and costs to adhere to local right-of-way and easement regulations may be required.
- Financing. Because SB-9 is relatively new and there may not be well-established lending practices in place, some mortgage holders and lenders may be hesitant to allow lot splitting or approve funding for novel projects.
As time passes and more SB-9 housing becomes commonplace, permitting staff and lenders will become more familiar with these types of projects. Uniformity in regulations and lending practices should emerge, and these challenges should smooth themselves out.
Regardless, SB-9 not only quadruples the number of dwellings that can be built on a single-family parcel, it quadruples the benefits! It opens up unprecedented opportunities for property owners looking to maximize their property’s financial potential through home sales or rentals, for households looking to buy or rent that are locked out of expensive housing markets, and for those looking to live in a multigenerational setting by sharing property with relatives.
How is AB-1033 different from SB-9, and which one is right for me?
AB-1033 and SB-9 allow homeowners to subdivide their lots and build (and sell) extra units, or even a portion of their land. Both laws aim to lessen California’s grinding housing crisis by adding extra homes that are more compact and affordably priced. Together, they create a market for approximately $750 billion of backyard land value that restrictive zoning has locked up for decades.
It is important to note that AB-1033 and SB-9 differ in some key details:
- Housing types. SB-9 deals with duplexes and lot splits, not ADUs. While SB-9 allows homeowners to split a portion of their land as-is or build another unit on their property, AB-1033 specifically addresses condo-ized ADUs. Rather than selling a portion of a lot, AB-1099 allows homeowners to sell their ADUs as condos.
- Eligibility. While SB-9 is a statewide requirement–meaning your city must allow you to pursue eligible developments as long as your property meets the qualifications–AB-1033 only gives cities the option to permit condo-ized ADUs. It is up to local jurisdictions whether or not they will allow it.
- Zoning. SB-9 is restricted to lots zoned for single-family, while AB-1033 offers municipalities the flexibility to consider other lot types.
When deciding which option is best for you, consider:
- The size of your lot. ADUs have a size restriction of 1,200 square feet and only three are allowed per lot, while SB-9 provides more flexibility with the sizes and number of homes that are classified as single-family homes or duplexes.
- Extra costs and complexities. Lot splits under SB-9 can be an expensive and lengthy process which may add costs and time to your home redevelopment. Legal expenses and the administrative lift to establish and maintain a homeowners association for a condo-ized ADU under AB-1033 may also add cost and burden.
- The goals of your home redevelopment. While selling a portion of your lot with a house or duplex may bring you a higher return on investment, a condo-ized ADU may better serve your friends and neighbors, like young families seeking entry-level homes or older adults that are looking to downsize.
The choice between the two depends on your specific circumstances and objectives. Both offer paths toward maximizing the value of your property while providing needed housing in your neighborhood.
How do I get started?
Contact Type Five to explore your options, discuss your home redevelopment goals, and get started on your home project!

Rhey Haggerty, Guest Writer
Urban Planner

Tim Thimmaiah
CEO, Co-founder