Can You Split a Bay Area Lot Under SB 9? What Owners Need to Know

WHAT: What Is An SB 9 Urban Lot Split?

An SB 9 urban lot split is a state-created pathway that can divide one qualifying single-family residential parcel into two parcels. The process is ministerial when the application meets the applicable requirements, which means the city reviews it against objective rules instead of treating it like a discretionary rezoning request.

The word “qualifying” does most of the work. SB 9 is not permission to split every large backyard in Palo Alto, San Jose, San Francisco, or another Bay Area city. The parcel, existing housing, location, access, hazards, and proposed homes all matter.

WHAT: What Can The New Parcels Potentially Hold?

HCD’s 2026 fact sheets explain that after an urban lot split, the local agency must allow up to two units on each resulting parcel when the project satisfies the law. Those units can be combinations of primary units, an ADU, or a junior ADU, subject to the two-unit limit on each lot created through the split.

That creates several possible strategies. An owner might create one home on each parcel, build two primary units on each parcel, or combine a primary home with an ADU or JADU. More units can mean more housing and potentially more value, but it also means more design, utility, financing, construction, and management complexity.

HOW: The Basic Eligibility Screen

The first screen is the parcel itself. Government Code section 66411.7 generally requires the parcel to be in a single-family residential zone and within a city or urbanized area or urban cluster. The proposed split must create no more than two parcels of approximately equal area, with one parcel at least 40% of the original and both generally at least 1,200 square feet unless a local ordinance allows smaller lots.

The site also has to survive the exclusions. The statute addresses protected affordable or rent-controlled housing, recent tenant occupancy, historic districts and listed historic resources, prior SB 9 lot splits, adjacent prior splits, and other conditions. A planning counter or architect should review the parcel before the buyer assigns value to the idea.

HOW: Access, Setbacks, Parking, And Utilities Still Matter

SB 9 limits how much a city can use objective standards to physically block a qualifying project, but it does not eliminate site design. The city may require easements for utilities and public services, access to or adjacency with the public right-of-way, and objective design and subdivision standards.

Parking can still matter, although state law limits when a city may require it. The project may also face slope, drainage, fire access, sewer, water, electrical, tree, coastal, flood, or geologic constraints. A parcel map is only one part of the development plan.

HOW: A Hypothetical Bay Area Case

Imagine a 12,000-square-foot single-family parcel in an urbanized Bay Area city. The existing home sits toward the front, the rear yard has street access or a practical access easement, utilities can be extended, and the property is not historic or tenant-protected. A simple concept could divide the parcel into two approximately 6,000-square-foot lots.

Option A is one primary home on each lot. Option B is one primary home plus another qualifying unit on each lot, subject to the SB 9 unit-count framework and local standards. Option C is to preserve the main home, use one parcel for a new primary home, and add an ADU or JADU where the rules allow it.

The important point is that the “case” is not proven by lot size alone. The buyer still needs a survey, preliminary site plan, planning review, utility review, construction estimate, financing model, and resale or rental analysis.

WHY: Why Owners And Buyers Pursue Lot Splits

The main reason is scarcity. In job-rich areas, a small increase in legal housing capacity can be valuable because the location already has demand from workers, families, renters, and buyers who want to stay close to employment and daily life.

A lot split can also unlock choices. An owner may want to house parents, create a rental, keep one home and sell another, build for multiple family members, or create a future exit plan. A developer or buyer may value the land because the existing house is not the only possible use.

But maximizing land use does not mean maximizing unit count at any price. A smaller, well-designed project that can actually be permitted, financed, built, rented, and sold may be stronger than a theoretical four-unit plan that collapses under utility, construction, or financing costs.

WHY: The Three Numbers That Decide Whether It Works

First is buildable area: how much space remains after setbacks, access, parking, fire, utilities, and objective design standards. Second is all-in cost: survey, design, permits, fees, demolition, construction, financing, contingency, and carrying cost. Third is finished value: realistic nearby sales and rent, not the highest listing in the neighborhood.

When those three numbers align, a lot split can turn underused land into additional housing and a more flexible asset. When they do not align, the “potential” belongs in the risk column rather than the offer price.

• Ask the city or county for the current SB 9 and ADU application checklist.
• Have a licensed surveyor or qualified design professional map the parcel and access.
• Confirm tenant, historic, hazard, coastal, and utility constraints.
• Compare the finished plan with real sales and rent comps.
• Use a written construction budget with contingency before paying a land premium.