Understanding Senate Bill 9 and Senate Bill 10: How New Legislation Affects California

California has long been a state of big property dreams—and increasingly, limited housing. As home prices continue to rise and inventory remains tight in desirable markets across the state, lawmakers are seeking effective ways to increase housing supply without compromising the character of existing neighborhoods.

Two significant legislative efforts—Senate Bill 9 (SB 9) and Senate Bill 10 (SB 10)—took effect on January 1, 2022, introducing sweeping changes to the zoning and development of residential land. These bills are part of a larger initiative tied to the California Comeback Plan, with a shared goal: to address the state's housing crisis through gentle, localized density increases.

For property owners, buyers, and real estate investors in California, these laws introduce new opportunities—as well as questions—about what's allowed, what's changing, and where this all leads. Let's explore the key takeaways and the potential implications for residential real estate across the state.

The implications of SB 9, often referred to as the "duplex law," go far beyond that simple label. Designed to incrementally expand housing in single-family neighborhoods, SB 9 empowers homeowners to split their lot and/or build a second unit—essentially legalizing fourplexes on qualifying single-family parcels. There are two core provisions of SB 9—Urban Split Lots and By-Right Two-Unit Development.

Under SB 9, qualifying homeowners may now split a single-family zoned lot into two parcels, without needing a public hearing or extensive discretionary review by the city.

To qualify:

• Each new lot must be at least 1,200 square feet, with no more than a 60/40 size imbalance between the two.
• The property must be located in a single-family residential zone within an urbanized area or urban cluster as defined by the U.S. Census Bureau—criteria met by most California cities.
• The split must not involve affordable housing, rent-controlled units, or properties occupied by tenants within the last three years.
• It must not be in a historic district or involve a property with historic landmark designation.

The owner and affiliates cannot have used SB 9 to split an adjacent parcel.

In addition to or separate from lot splitting, SB 9 allows for the construction of up to two residential units per lot—also by right, meaning local agencies must approve them without public hearings, provided the proposed project meets basic criteria.

These units can be:

• Two entirely new homes
• An existing home with a newly added second unit (such as a detached ADU)

Again, the parcel's location must be in a single-family zone within an urban area, and tenant protections and historic designations apply similarly to the lot-split provision.

Together, these changes mean that a qualifying property in a standard single-family neighborhood could now support up to four homes—a notable shift from the prior one-home-per-lot standard.

While SB 9 focuses on what individual homeowners can do, Senate Bill 10 provides local governments with more flexibility to proactively increase housing density in transit-friendly areas—and do so without getting bogged down in red tape.

This bill allows city and county governments to rezone parcels to allow up to ten residential units per lot, if those parcels are in:

• Transit-rich areas
• Urban infill zones

The key difference with SB 10? It maintains local control. The law authorizes zoning changes but does not require them. Each city must opt in by passing a local ordinance via a two-thirds vote of its governing body. That means your local planning commission or city council still decides whether, where, and how this density increase occurs.

• Enables middle-density housing, bridging the gap between single-family homes and mid-rise apartments.
• Helps cities plan for housing growth near transportation hubs, which can reduce traffic congestion and lower emissions.
• Provides a legal pathway to override previous ballot initiatives that might prohibit this kind of upzoning—if a supermajority agrees.

Perhaps most importantly, SB 10 streamlines the process by allowing these zoning changes to bypass certain legal obstacles, including prolonged environmental reviews under the California Environmental Quality Act (CEQA), which often stall housing development.

For California homeowners, real estate developers, and investors, the implications of SB 9 and SB 10 are both practical and philosophical. At their core, these bills are about flexibility and opportunity—opening the door to new housing formats, configurations, and ownership possibilities.

Here's how this legislation might affect you:

• You may now split your lot or build additional units, increasing your property's value or providing housing for family members.
• Your neighborhood could gradually densify, especially in highly desirable areas, bringing both vitality and change.
• Your local jurisdiction may soon consider zoning adjustments under SB 10, which could alter the character of nearby blocks.

• Consider the long-term development potential of a property—not just its current structure.
• A single-family parcel today might be eligible to house multiple residences tomorrow.

• SB 9 presents an avenue for gentle infill projects, which were at one time restricted by zoning.
• SB 10 may unlock larger-scale redevelopment opportunities in areas well-served by transit.

Projects aligned with these laws may enjoy fewer bureaucratic hurdles, making them more financially viable.

Of course, any significant zoning change stirs debate—and rightly so. Critics argue that statewide mandates may override thoughtful local planning or strain existing infrastructure. Proponents say that California's housing shortage will not resolve itself, and these bills provide practical, scalable solutions.

What remains true is this: housing policy in California is changing, and these laws represent a pivot toward smart density and ownership opportunities—especially in established, high-demand communities.

Senate Bills 9 and 10 are not silver bullets, but they do mark a shift in how California approaches housing growth. With an emphasis on local implementation, gentle density, and fewer regulatory hurdles, these bills create new possibilities for how we live, invest, and build in the Golden State.

If you're thinking about buying, selling, or developing real estate in California, now is the time to understand how these laws may shape your options—and your strategy.

Have questions about how SB 9 or SB 10 could impact your property? Or looking for more California real estate guidance?

Whether you're navigating a luxury transaction or want to understand the fine print behind the paperwork, contact Consumer's Title Company today. Our team's extensive experience and range of services across all 58 of California's counties promise the support and guidance necessary to help you protect your most vital asset.