SB 9, signed September 16, 2021 and effective January 1, 2022, is a California lot split and two unit law, not an ADU law. It lets an owner ministerially split a single family lot into two parcels, each at least 1,200 square feet, and build two units per parcel.
Last verified: September 25, 2026 against the California Legislature bill text for SB 9 (2021, Atkins), Chapter 162, Statutes of 2021, at leginfo.legislature.ca.gov, adding Government Code Sections 65852.21 and 66411.7.
An accessory dwelling unit, or ADU, is a second, smaller home on a lot that already has a house. A junior ADU, or JADU, is a unit of up to 500 square feet created inside the walls of an existing house. SB 9 is not an ADU law, but it interacts with ADUs, and this page explains that interaction using the enacted statute.
Which SB 9 is this?
Two different California laws share the number SB 9. This page covers the 2021 SB 9 by former Senator Atkins, a lot split and two unit law that became Chapter 162, Statutes of 2021. It is a separate statute from the 2025 SB 9 by Senator Arreguin, an ADU enforcement law that took effect January 1, 2026 and is covered on the California ADU law tracker. The two bills share a number only. Everything below refers to the 2021 lot split law.
What does SB 9 allow?
By right means a use is allowed without a special permit, and ministerial approval means a city must approve a qualifying application without discretionary review or a public hearing. SB 9 gives owners of single family lots two ministerial rights. First, under Government Code Section 65852.21, an owner may build up to two units on a single family zoned parcel through ministerial approval. Second, under Government Code Section 66411.7, an owner may split one single family lot into two parcels through an urban lot split, also ministerially. Governor Newsom approved SB 9 on September 16, 2021, and it took effect January 1, 2022.
A lot split is the division of one legal parcel into two separate legal parcels. Under SB 9, each new parcel created by an urban lot split must be at least 40 percent of the size of the original lot and at least 1,200 square feet.
| Rule | California standard | Statute | Source |
|---|---|---|---|
| Two units in single family zones | A parcel may hold up to two units, approved ministerially | Gov. Code 65852.21 | Ch. 162, Statutes of 2021 |
| Urban lot split | One single family lot may be split into two parcels, approved ministerially | Gov. Code 66411.7 | Ch. 162, Statutes of 2021 |
| Minimum new parcel size | Each new parcel must be at least 40 percent of the original lot and at least 1,200 square feet | Gov. Code 66411.7 | Ch. 162, Statutes of 2021 |
| Effective date | January 1, 2022 | Ch. 162, Statutes of 2021 | Ch. 162, Statutes of 2021 |
How does SB 9 interact with ADUs?
This is the key point for ADU owners. Under SB 9, a local agency is not required to also permit an ADU or a JADU on a parcel that uses both the two unit authority in Government Code Section 65852.21 and the lot split authority in Government Code Section 66411.7. The statute states that “a local agency shall not be required to permit an accessory dwelling unit or a junior accessory dwelling unit on parcels that use both the authority contained within this section and the authority contained in Section 66411.7.” In practice, this means an owner who both splits the lot and builds two units on a parcel may lose the guaranteed right to add an ADU or JADU on that parcel. Owners therefore face a choice between using SB 9 to its fullest and preserving a guaranteed ADU.
How many units can SB 9 produce?
SB 9 stacks two separate rights, so the combined count depends on which rights an owner uses. On a single lot without a split, Section 65852.21 allows up to two units. An urban lot split under Section 66411.7 divides the lot into two parcels, and the two unit authority can apply on each parcel, which can yield up to four units across the original lot. Because a local agency is not required to permit an ADU or JADU on a parcel that uses both authorities, the four unit path and the extra ADU path do not automatically combine. An owner who wants a guaranteed ADU or JADU may prefer not to use both SB 9 authorities on the same parcel.
What can local governments still regulate?
SB 9 sets the minimum parcel size for a lot split at 40 percent of the original lot and at least 1,200 square feet, under Government Code Section 66411.7. The right to two units and the right to a lot split are ministerial, so a city cannot subject a qualifying SB 9 application to discretionary review or a public hearing. This page does not restate every local objective standard that SB 9 preserves. Confirm the specific standards your city applies to an SB 9 lot split or two unit project with your local planning department.
How SB 9 connects to other California ADU laws
SB 9 sits alongside California’s dedicated ADU statutes, each covered on its own page.
- The 2025 SB 9 by Senator Arreguin is an ADU enforcement law and a different statute from this 2021 lot split law. See the California ADU law tracker.
- AB 2533 is a separate California ADU law.
- AB 1033 lets a city opt in to allowing an ADU to be sold separately as a condominium.
- SB 1211 allows up to eight detached ADUs on a lot with an existing multifamily building.
For the full statewide rules on ADU size, setbacks, height, parking and fees, see the California ADU law and permits pillar. You can also browse the ADU laws library.
What changed in 2026?
SB 9 itself was enacted in 2021 and took effect January 1, 2022. Its lot split and two unit provisions in Government Code Sections 65852.21 and 66411.7 continue to operate. The 2025 SB 9 that took effect January 1, 2026 is a different ADU enforcement statute and did not change the 2021 lot split law.
What changes in 2027?
No further statewide California SB 9 lot split changes are scheduled as of September 25, 2026. We recheck the California Legislature each session and will update this page when a relevant bill is chaptered.
Frequently Asked Questions
Is SB 9 an ADU law?
No. The 2021 SB 9 is a lot split and two unit law, not an ADU law. It adds Government Code Sections 65852.21 and 66411.7, and it interacts with ADUs but does not set ADU standards.
Is the 2021 SB 9 the same as the 2025 SB 9?
No. The 2021 SB 9 by former Senator Atkins is a lot split and two unit law that took effect January 1, 2022. The 2025 SB 9 by Senator Arreguin is a separate ADU enforcement law that took effect January 1, 2026. They share a bill number but are different statutes.
How small can each parcel be after an SB 9 lot split?
Each new parcel created by an SB 9 urban lot split must be at least 40 percent of the size of the original lot and at least 1,200 square feet, under Government Code Section 66411.7.
Can I build an ADU on a lot that uses SB 9?
A local agency is not required to permit an ADU or JADU on a parcel that uses both the two unit authority in Government Code Section 65852.21 and the lot split authority in Government Code Section 66411.7. Owners who want a guaranteed ADU may choose not to use both authorities on the same parcel.
When did SB 9 take effect?
Governor Newsom approved SB 9 on September 16, 2021, and it took effect on January 1, 2022. It became Chapter 162, Statutes of 2021.
Sources
- California Legislature, SB 9 (2021, Atkins), lot splits and two unit development, text: https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202120220SB9
- California Legislature, SB 9 (2025, Arreguin), ADU enforcement, for disambiguation: https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260SB9
Disclaimer
This page is general information, not legal advice. Housing law changes often and cities apply it differently. Confirm the current rules with your local planning department before you build or split a lot.
Related ADU laws
Other laws and rules in the same silo, kept in step as each one goes live.