California SB 9, in effect since January 1, 2022, lets the owner of a qualifying single-family lot build a second home on the property, split the lot into two parcels, or do both, with the local agency required to approve the project ministerially instead of putting it through a public hearing. Also known as the California HOME Act, the law can ultimately produce up to four units where one house stood before.
What You Can Build
SB 9 opens two pathways, and you can use one or combine them.
The first is duplex development under Government Code Section 65852.21. You keep your lot as a single parcel and add a second primary unit, for a total of two. The local agency must approve it ministerially as long as the project meets objective standards.1California Legislative Information. California Government Code 65852.21 – Housing Development
The second is an urban lot split under Government Code Section 66411.7. You subdivide your lot into two parcels and build up to two units on each, for a maximum of four. The resulting lots must be roughly equal, with neither smaller than 40 percent of the original parcel area, and each new lot must be at least 1,200 square feet unless a local agency has adopted a smaller minimum.2California Legislative Information. California Government Code 66411.7 – Urban Lot Split If your existing lot is small, the minimum size requirement is often the deal-breaker.
Lot splits carry extra conditions. The applicant must sign an affidavit committing to live in one of the units as a primary residence for at least three years after approval; community land trusts and qualified nonprofit corporations are exempt. The law also blocks serial splitting: a parcel created through an SB 9 split cannot itself be split again, and an owner who has already split an adjacent parcel under SB 9 cannot split a second one.2California Legislative Information. California Government Code 66411.7 – Urban Lot Split These guardrails exist to discourage investors from buying single-family homes purely for rapid subdivision and resale.
Whether Your Lot Qualifies
Not every single-family lot is eligible. The parcel must sit within a city whose boundaries include at least part of an urbanized area or urban cluster as designated by the U.S. Census Bureau, or, for unincorporated land, the parcel must fall entirely within such an area.1California Legislative Information. California Government Code 65852.21 – Housing Development The property must currently be zoned for single-family residential use.
Beyond zoning, SB 9 projects are barred on parcels with certain environmental or safety conditions: prime farmland, wetlands, high fire hazard severity zones, flood-risk areas, earthquake fault zones, wildlife habitat areas, and conservation easements. Properties on the State Historic Resources Inventory or designated as a city or county landmark are also ineligible.3California Department of Housing and Community Development. SB 9 Fact Sheet Local planning departments maintain maps of these constraint zones, and checking them early saves time and money.
One important caveat: if your property is inside a homeowners association, the HOA board can choose whether to allow or prohibit SB 9 projects, and private CC&Rs may impose restrictions the statute does not address. Before paying for plans or surveys, read the governing documents and talk to the board.
Rules the City Must Follow
SB 9 sets a statewide floor for what cities and counties must allow. Local agencies cannot require side or rear setbacks greater than four feet. They can still set front setbacks, height limits, and design standards like roof pitch and facade materials, but no local rule can physically prevent construction of two units of at least 800 square feet each. Any objective standard that would make that impossible must be modified or waived.3California Department of Housing and Community Development. SB 9 Fact Sheet
Parking requirements are capped at one off-street space per unit. If the parcel sits near a transit stop as defined in the statute, the agency cannot require any parking at all. On many urban lots, that difference changes what will actually fit.
One rule is absolute: units created through SB 9 cannot be rented for periods shorter than 30 days. The ban applies to both duplex units and anything built on lots resulting from an urban lot split, and local governments cannot override it. If your plan depends on short-term rental income, SB 9 is the wrong tool.
Tenant Protections That Can Disqualify Your Project
SB 9 builds in protections meant to stop homeowners from evicting tenants to pursue a project, and these are among the most commonly misunderstood provisions in the law.
You cannot demolish or alter housing that has been occupied by a tenant within the past three years. The rule covers rent-controlled units and deed-restricted affordable housing. If the owner used Ellis Act withdrawal rights to remove a rental unit from the market within the past 15 years, the parcel is entirely ineligible. And even where no unit is being demolished, if a tenant has lived on the property within the past three years, the project cannot remove more than 25 percent of the home’s existing exterior walls.1California Legislative Information. California Government Code 65852.21 – Housing Development
How SB 9 Interacts with ADUs
SB 9 and California’s accessory dwelling unit laws work together, but the unit math changes depending on whether you split your lot.
On a lot that stays whole, you can combine SB 9 primary units with ADUs or junior ADUs built under separate ADU law. The total still cannot exceed four units on the parcel.3California Department of Housing and Community Development. SB 9 Fact Sheet
On lots created through an urban lot split, the limit is stricter. Each resulting lot caps at two total units, and primary units, ADUs, and junior ADUs all count toward that cap.3California Department of Housing and Community Development. SB 9 Fact Sheet On each split lot, the options are two primary units, a primary unit plus an ADU, or a primary unit plus a junior ADU. The four-unit ceiling across both lots still applies. If you already have an ADU and are considering a split, pay attention to which new parcel the ADU ends up on, because that unit counts against the two-unit limit for that lot.
Applying and Getting Approved
SB 9 applications are reviewed ministerially. The local agency measures your project against objective, pre-established standards without discretionary judgment, public hearings, or review under the California Environmental Quality Act.3California Department of Housing and Community Development. SB 9 Fact Sheet If the project meets the criteria, approval is required.
For urban lot splits, the statute sets a firm 60-day clock. If the agency has not approved or denied a complete application within 60 days, the application is deemed approved automatically.2California Legislative Information. California Government Code 66411.7 – Urban Lot Split That provision gives the law real teeth.
A local agency can deny an SB 9 project only if its building official makes a written finding, based on a preponderance of the evidence, that the project would have a “specific, adverse impact” on public health, safety, or the physical environment. The impact must be significant, quantifiable, direct, and unavoidable, with no feasible way to mitigate it.3California Department of Housing and Community Development. SB 9 Fact Sheet General concerns about neighborhood character or traffic do not meet the standard.
If a local agency wrongfully denies a qualifying application or imposes conditions that effectively block it, the California Department of Housing and Community Development has enforcement authority over SB 9 as of January 1, 2024. Filing a complaint with HCD is the primary recourse when a city or county is not following the law.
What It Actually Costs and Why Uptake Has Been Low
On paper the law is powerful. In practice, uptake has been modest. Data from the first year showed limited applications across most surveyed jurisdictions, with high construction costs, rising interest rates, and unfamiliarity with the process keeping many homeowners on the sidelines. Planning departments reported heavy inquiry volume that rarely turned into submitted applications. In some cities, homeowners chose ADUs instead, because ADU law is more established and comes with incentives like reduced impact fees.
Costs run well beyond the application fee. California construction runs several hundred dollars per square foot depending on region and build method. Architecture, engineering, and project management typically add 15 to 20 percent on top of hard construction costs. Local development impact fees and school fees vary widely and can add tens of thousands of dollars per unit, and recording a final parcel map carries its own county fee. None of this is standardized statewide, so pulling jurisdiction-specific numbers early is the only way to tell whether an SB 9 project pencils out.