In one of our recent posts, we covered the introduction of Senate Bill 9 (SB9) and what it means for California’s residential properties. Today, we’re digging deeper, looking at the details of the new rules and providing a full explanation of SB9’s terms. 

What is the Purpose of SB9?

California’s government has recognized that big changes need to be made if the state wants to solve its housing crisis. This includes rethinking the density limitations of single-family zoning. 

Across America, over 75% of residential land is currently zoned as single-family. This restrictive zoning policy widens existing wealth gaps and damages upward mobility—especially for younger generations. 

Due to rules that inhibit efficient use of land, single-family zoning effectively prohibits the construction of smaller, lower-cost homes in desirable neighborhoods. Only those with high incomes are able to access housing in areas that have attractive amenities, good schools, and promising job opportunities.

SB9 was introduced to remove the single-family limitations, instead allowing duplexes to be built on residential lots without excessive red tape. Moreover, SB9 actually allows original residential lots to be split one time, creating the opportunity to build two duplexes on what was once a single-home lot. 

With this new path in place, the government has given California’s homeowners a chance to contribute more housing to the market by developing duplexes or fourplexes on their properties. 

Why is SB9 Controversial?

Opening the door for denser development in residential areas has caused a lot of concern among some Californians. Citizens worry that the increased density will ruin the charm and peace found in their single-family neighborhoods, and also fear that speculative development will result in unattractive, low-quality construction. However, SB9 was written with these concerns in mind, including a variety of stipulations that will prevent these negative impacts. 

SB9 Criteria

SB9 places stringent regulations on qualifying projects and applicants. For instance, to prevent unscrupulous development, property owners must use one of the units as their primary residence for at least three years.


Under SB9, local agencies are legally bound to approve certain lot subdivisions ministerially. 

Ministerial approval means that no judgment or deliberation is required by the local agency, thereby removing the extra steps of discretionary reviews or public hearings. Californians have the right to lot splits when specific conditions are met.

The following criteria must apply for “by-right” lot splits:

  • Each new lot is at least 1,200 square feet
  • The new lots are of roughly equal size (a 60/40 split minimum)
  • The split doesn’t necessitate the demolition of affordable or rent-controlled housing, or properties occupied by tenants in the last three years
  • The lot is located in a single-family residential zone
  • The lot isn’t a historic landmark or within a designated historic district
  • The lot is within a city with urbanized areas or clusters, or within an urbanized area or urban cluster itself
  • The original lot wasn’t created by an SB9 lot split
  • The owner hasn’t previously subdivided adjacent lots through SB9

The following objective zoning standards may be enforced by local agencies:

  • One off-street parking space per unit can be required if it isn’t in close proximity to transit or car sharing hubs
  • Side and rear setbacks may be imposed, except with existing structures (or projects constructed to exactly the same dimensions as the original home)
  • Non-residential use of the new lots is prohibited
  • Owners must occupy one of the housing units for at least three years after approval

SB9’s new rules mean local agencies cannot:

  • Prohibit connected or adjacent structures
  • Require right-of-way dedications or construction of off-site improvements
  • Require correction of non-confirming zoning conditions
  • Deny a qualifying SB9 project unless it has a specific negative impact on public health and safety, with no feasible mitigations

Two-Unit Developments

In addition to the by-right urban lot splits, local agencies must allow for two-unit developments on these new SB9 lots. This can mean building two new units, or simply adding one additional unit. 

Again, both of these types of projects need to be ministerially approved, without discretionary reviews or hearings. Property owners therefore avoid a lengthy, frustrating, and expensive process to obtain project approval.

For property owners to have the right to two-unit developments, the following criteria must apply:

  • The project is located in a single-family residential zone
  • It is within an urbanized area or cluster (or a city containing such areas)
  • It doesn’t involve the removal of tenanted, affordable, or rent-controlled housing
  • It doesn’t involve demolition of more than 25% of exterior walls (of the existing dwelling), unless specifically allowed by the local agency, or not tenant-occupied for the last three years
  • The site isn’t within a historic district or a historic landmark itself

The following objective zoning standards may be enforced by local agencies:

  • Short-term rentals are prohibited in residences created under SB9
  • Additional ADUs or JADUs need standard approvals, but do not need special approvals
  • Coastal Act conservation requirements for coastal resources and areas (However, the California Environmental Quality Act does not apply)

Tentative Subdivision Maps

Tentative maps are typically required for property subdivisions (lot-splits). These maps are meant to show the existing conditions of a property and its parcel lines, including boundaries, topography, easements, and current utility services. Maps must reflect any newly proposed configurations, grading, drainage plans, roadways, and utility locations (as well as their delivery methods).

Each local agency has their own specific processes and requirements for submitting a tentative map. This has traditionally included limitations on the term tentative subdivision maps remain valid. However, SB9 has extended the lifespan of tentative subdivision maps. They are now generally valid for up to two years after approval. An extension of up to four years has been put in place for projects requiring substantial public improvement obligations.

California SB9 Summary

The California SB9 bill gives qualifying properties a simplified process to split lots and create multiple units on land that would otherwise be zoned for a single-family dwelling. It permits lots to be split in two and allows for a two-unit project on each new lot, resulting in four dwellings total. Only ministerial approval is required, reducing much of the red tape that would normally de-incentivize this type of development.

SB9 aims to facilitate residential construction across California, sparking the creation of more affordable homes in already existing neighborhoods. By leveraging SB9, California’s homeowners are able to contribute their own solutions to the housing crisis while increasing their own property values. 

Make the Most of SB9 with Letter Four

If you’re a homeowner that’s interested in upgrading your property under the new SB9 rules, Letter Four can help. We have already assisted residents with achieving outstanding SB9 builds, adding value to properties and creating new income opportunities for owners. 

Our Design-Build team offers complete architectural and construction services, and can even assist with selecting the perfect new lot for an SB9 project. We’ll help you with every step, saving you time and money in the process. If you’d like to explore how to kick things off, take a look at our Project Action Plans, or contact us today to schedule a consultation