"SB 9" is one of the most-searched housing terms in California. It's also widely misunderstood. It is not an ADU law, but it often competes with ADUs for the same backyard. This guide explains what SB 9 allows, how it differs from building an ADU, and how to choose.
A naming note: this article covers SB 9 of 2021 (Atkins), the duplex and lot-split law. The Legislature reused the bill number in 2025: a separate SB 9 of 2025 changed how local ADU ordinances are reviewed by HCD. We cover that one on our California ADU laws page.
What SB 9 (2021) allows
SB 9 added Government Code sections 65852.21 and 66411.7. On most lots in single-family zones, it requires cities and counties to ministerially approve:
- A two-unit project. That means up to two primary homes on one lot, either a duplex or two detached houses.
- An urban lot split. One lot becomes two, each generally at least 1,200 sq ft and no smaller than about 40% of the original lot.
Combined, a lot split plus two units on each new lot can yield up to four homes where one stood before.
Local agencies may apply objective standards, but they must allow units of at least 800 sq ft with 4-foot side and rear setbacks. Lots are excluded in certain cases:
- historic districts
- very high fire hazard severity zones, unless mitigated
- sites where the project would demolish affordable or rent-controlled housing, or housing occupied by tenants in recent years
- other listed environmental constraints
The owner-occupancy affidavit
For an urban lot split, the applicant must sign an affidavit stating they intend to live in one of the units as their primary residence for at least three years after the split. Investors generally can't use the lot-split path. The two-unit path without a split doesn't carry the same affidavit requirement.
By contrast, cities cannot require owner occupancy for an ADU (Gov. Code section 66315). That's one reason ADUs are often the simpler choice.
How SB 9 interacts with ADUs
- On a lot that has not been split, you can generally use SB 9 for two units and still add ADUs and JADUs under State ADU Law. Local rules vary.
- On a lot created by an SB 9 lot split, a city may cap total units at two per lot, counting ADUs and JADUs. Many SoCal cities apply this cap.
SB 9 vs ADU: side by side
- Ownership: an SB 9 lot split creates a separately sellable lot. A standard ADU can't be sold separately, unless your city has opted into AB 1033 condo conversions (see our AB 1033 guide).
- Size: an ADU is typically capped at 850–1,200 sq ft depending on bedrooms and local rules. SB 9 units can be larger, subject to local objective standards.
- Fees: ADUs of 750 sq ft or less have no impact fees. SB 9 units are usually charged as new homes.
- Process: both are ministerial. A lot split also requires a parcel map, a surveyor and often new utility services, which adds months and cost.
- Owner occupancy: none for an ADU. A three-year affidavit for an SB 9 lot split.
Which path fits your goals?
- Rental income while you keep the property: an ADU, possibly paired with a JADU, is usually faster and cheaper.
- Selling part of the lot: SB 9 is the main route, and you'll need to live on site for the affidavit period.
- Housing family: either works. ADUs are simpler.
- Maximum unit count on a large lot: run both scenarios with an architect who knows your city's SB 9 ordinance.
SB 9 in Southern California
Uptake has been modest compared with ADUs. Lot splits involve mapping, surveying and utility costs, and many SoCal neighborhoods sit in fire, coastal or historic overlays. In Los Angeles, San Diego and Orange County cities, ADU permits still far outnumber SB 9 applications. Check your city's SB 9 page for local objective standards. Many cities post checklists alongside their ADU program information.
Updates since 2021
Later legislation, including SB 450 (2024), tightened SB 9 by limiting the local standards that can apply and setting a 60-day approval timeline for complete applications. Because SB 9 rules keep changing, confirm current requirements with your city planning department and the statute on leginfo.legislature.ca.gov.
Working with builders
Not every ADU builder takes on SB 9 projects. They involve subdivision mapping and often larger homes. When you interview builders, ask if they have completed an SB 9 project, who handles the parcel map, and how they coordinate the surveyor and civil engineer. Our directory's design-build firms are a good place to start.
Bottom line
For most Southern California homeowners who want extra living space or rental income, an ADU (plus a JADU) remains the faster, cheaper and less restrictive option. SB 9 makes sense mainly when you want to create a separately sellable lot and you plan to live there for the next three years.
Frequently asked questions
What is SB 9 in California?
SB 9 (2021) requires cities to ministerially approve up to two homes on most single-family lots and an urban lot split into two lots, which can allow up to four units in total.
Is SB 9 the same as an ADU?
No. SB 9 creates primary units and new lots. ADUs are accessory units under a separate State ADU Law with their own size, fee and approval rules.
Do I have to live on the property to use SB 9?
For an urban lot split, the applicant must sign an affidavit of intent to live in one unit for three years. ADUs have no owner-occupancy requirement.
Can I build ADUs on an SB 9 lot?
On an unsplit lot, usually yes. On lots created by an SB 9 split, cities may cap the total at two units per lot, including ADUs.
What is SB 9 of 2025?
A separate 2025 bill with the same number that makes non-compliant local ADU ordinances void if they are not submitted to HCD or HCD's findings are not answered on time.
This page is general information, not legal, tax or financial advice. Costs vary by property and builder. Images are AI-generated illustrations. Last updated November 2026.