Lot Splits and Urban Housing
How California’s SB 9 Law Can Turn One Residential Property Into Multiple Housing Opportunities
For generations, one of the most basic assumptions in California real estate was simple:
One single-family lot meant one primary home.
California’s housing laws have changed that.
Under Senate Bill 9 (SB 9), qualifying properties in single-family residential zones can potentially be divided into two parcels, developed with additional primary dwelling units, or both.
For homeowners, this creates new ways to use their property.
For builders and real estate investors, it creates something even more interesting:
Development potential that may not be obvious from looking at the existing property.
What Is SB 9?
SB 9 became effective January 1, 2022 and created two important development opportunities on qualifying properties in single-family residential zones:
Two-Unit Development
A qualifying property may be developed with up to two primary residential units.
Urban Lot Split
A qualifying existing parcel may be divided into two separate parcels.
These provisions can also be used together.
Under the right circumstances, SB 9 can facilitate the creation of up to four housing units within the lot area that traditionally might have contained one single-family home.
What Is an Urban Lot Split?
An Urban Lot Split is a subdivision authorized under SB 9.
Instead of going through the traditional discretionary subdivision process, a qualifying SB 9 lot split must be reviewed ministerially.
That distinction is important.
Ministerial review means the local agency evaluates the application against applicable objective requirements rather than deciding whether it likes the subdivision.
If the statutory requirements are satisfied, the agency generally must approve the split.
How Can One Property Become Four Units?
This is where SB 9 becomes particularly interesting.
Imagine an existing single-family residential parcel.
Depending on eligibility and site conditions, the owner may be able to:
Step 1: Divide the original property into two parcels.
Step 2: Develop up to two qualifying units on each resulting parcel.
The result can potentially be:
Original property → 2 parcels → up to 4 total housing units.
Importantly, the four-unit concept doesn’t necessarily mean four identical houses. HCD explains that when an SB 9 lot split occurs, the local agency must allow up to two units on each resulting parcel, and primary units, ADUs, and JADUs can count toward that two-unit-per-parcel limit.
There Are Rules for the New Lots
SB 9 doesn’t allow an owner to divide a property however they want.
Among the requirements, the resulting parcels generally must be roughly proportional in size, with neither parcel smaller than 40 percent of the original parcel area.
Each resulting parcel generally must also be at least 1,200 square feet, although a local jurisdiction may establish a smaller minimum.
Local governments may also require easements for public services and utilities and require access to the public right-of-way.
Can Cities Still Apply Development Standards?
Yes—but their authority is limited.
Local governments may apply objective:
· Zoning standards.
· Subdivision standards.
· Design standards.
However, those standards cannot be used to effectively defeat SB 9.
For example, local standards generally cannot prevent the construction of qualifying units of at least 800 square feet each or prevent creation of two qualifying 1,200-square-foot parcels.
This connects directly to another topic we’ve discussed in this series: Objective Design Standards.
The question increasingly becomes:
Does the project comply with the objective rules?
Not:
Does someone at the city like the project?
What About Setbacks?
Local agencies generally may require rear and side setbacks of up to four feet for qualifying SB 9 housing development.
There are exceptions, including circumstances involving existing structures that already have smaller setbacks.
This can make development possible on properties where traditional setback requirements would otherwise leave insufficient buildable area.
What About Parking?
SB 9 also limits parking requirements.
A jurisdiction generally may require no more than one off-street parking space per unit.
And parking generally cannot be required when the parcel is:
· Within one-half mile walking distance of a high-quality transit corridor or major transit stop, or
· Within one block of car-share.
Again, the purpose is to prevent local development standards from making otherwise qualifying housing impossible to build.
Not Every Property Qualifies
This is extremely important.
SB 9 is not a blanket right to divide every residential parcel in California.
Eligibility depends on both the property and the proposed development.
Restrictions can involve properties affected by issues such as:
· Certain farmland.
· Wetlands.
· Very high fire hazard areas under specified circumstances.
· Hazardous waste sites.
· Flood zones and floodways under specified circumstances.
· Habitat conservation areas.
· Conservation easements.
· Historic properties or districts.
There are also protections involving existing tenants and certain affordable or rent-controlled housing.
That means SB 9 should always begin with a property-specific feasibility analysis, not an assumption that the parcel qualifies.
SB 450 Strengthened SB 9
As we discussed earlier in this series, California subsequently passed SB 450 after lawmakers concluded that some jurisdictions were creating additional obstacles to SB 9 projects.
SB 450 strengthened the original law and reinforced California’s expectation that qualifying SB 9 applications actually receive the streamlined treatment promised by state law.
HCD now specifically identifies Duplexes and Lot Splits under SB 9 among the state housing laws its Housing Accountability Unit has authority to enforce.
Why Investors Should Care
This is where SB 9 becomes particularly relevant to real estate investing.
Two properties that appear nearly identical on a listing website may have completely different development potential.
One may simply remain a single-family home.
Another may potentially support:
· A lot split.
· Additional primary units.
· ADUs or JADUs in qualifying configurations.
· Multiple rental units.
· Multiple legal parcels.
· Different long-term ownership or disposition strategies.
That means investors shouldn’t evaluate property solely by asking:
“What’s there?”
They should also ask:
“What can legally be created here?”
That second question can reveal value the market hasn’t fully recognized.
But Don’t Buy Based on SB 9 Without Doing Your Homework
The potential is real.
So are the constraints.
Before purchasing a property specifically for an SB 9 strategy, investors should evaluate issues such as:
· Zoning.
· Parcel size and configuration.
· Existing structures.
· Easements.
· Utilities.
· Sewer or septic capacity.
· Water availability.
· Fire access.
· Environmental constraints.
· Existing tenants.
· Title issues.
· Local objective development standards.
A parcel can look perfect on a map and become considerably less attractive once infrastructure or site constraints are understood.
State law may create the opportunity, but the property still has to physically support the project.
Rural California
SB 9 specifically focuses on qualifying properties within urbanized areas and urban clusters, so it is not a universal rural lot-splitting law.
Even where a property qualifies, rural and semi-rural projects can face very different feasibility questions than urban properties.
A lot split may look excellent on paper until you discover that each resulting parcel needs:
· Adequate wastewater capacity.
· Reliable water.
· Legal access.
· Fire apparatus access.
· Buildable area.
· Appropriate setbacks from environmental resources.
For rural investors especially, development potential and infrastructure capacity have to be evaluated together.
Common Misconceptions
“SB 9 lets me split any residential property.”
False.
The property and proposed project must satisfy specific statutory requirements.
“SB 9 automatically gives me four houses.”
False.
SB 9 can facilitate up to four units in the area traditionally used for one single-family home, but actual development depends on the parcel, the proposed configuration, infrastructure, objective standards, and other applicable laws.
“The city can simply refuse my lot split.”
Not if the project qualifies.
SB 9 requires ministerial approval of qualifying lot splits and housing developments, although a jurisdiction retains limited authority to deny a project where it would create a specific adverse impact on public health and safety or the physical environment that cannot be satisfactorily mitigated.
“A lot split automatically makes a project profitable.”
Definitely not.
Creating development rights and creating a profitable development are two different things.
Infrastructure, construction costs, financing, market demand, taxes, and permitting costs all matter.
Why This Matters
SB 9 illustrates one of the most important themes running through California’s recent housing legislation:
Existing zoning no longer tells you everything you need to know about a property’s development potential.
California has created additional development pathways through:
· SB 9.
· ADU laws.
· Density Bonus.
· Transit-oriented development.
· Ministerial approvals.
· Builder’s Remedy.
· Other housing legislation.
For homeowners, that can create flexibility.
For builders, it can create projects.
For investors, it can create value that isn’t immediately obvious.
The Bottom Line
Lot splitting isn’t new.
What’s new is California creating a statewide, ministerial pathway that allows qualifying single-family residential properties to be divided and developed with additional housing.
SB 9 doesn’t make every property developable.
It doesn’t eliminate infrastructure constraints.
And it doesn’t guarantee that every project makes financial sense.
What it does is create another tool.
And in real estate investing, understanding tools that other buyers overlook can be the difference between seeing one house on one lot and seeing the development opportunity hidden underneath it.
Looking Ahead
In our next article, we’ll examine Accessory Dwelling Unit Updates and explain how California has continued expanding ADU rights, including where ADUs can be built, how many may be allowed, and why ADUs have become one of the most accessible ways to increase housing and property income.
If you’re considering a lot split or evaluating a property’s development potential, Buchanan Land Use Consulting can help determine what state law allows, identify site-specific constraints, and navigate the subdivision and permitting process.
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