SB 9 is a California law, in effect since January 1, 2022, that requires cities to approve two homes on most single-family lots, or to split one lot into two, without a public hearing. With a lot split, each new parcel can hold up to two units. That’s up to four homes where one used to be.
That’s the 60-second answer. The rest of this page gives you the key rules in one table, what changed from 2024 to 2026, and links to our longer guides when you’re ready to run numbers on a specific lot.
SB 9 in plain English
Senate Bill 9, also called the California HOME Act, added two tools to state law:
- Two-unit development (no split). Build a second primary home on a single-family lot, or turn the existing house into a duplex. ADUs and JADUs can still be added where ADU law allows them.
- Urban lot split. Divide one single-family parcel into two parcels you can sell separately, with up to two units on each.
The important word is ministerial. If your project meets the objective standards, the city has to approve it. There’s no hearing, no neighbor appeal and no planning commission vote. The state’s HCD SB 9 fact sheet is the official summary.
SB 9 quick facts
| Rule | What the law says |
|---|---|
| Effective date | January 1, 2022 (amended by SB 450, effective January 1, 2025) |
| Where it applies | Lots in single-family residential zones in cities and urbanized parts of counties |
| Maximum units | Two primary units per lot. After a lot split, cities can cap each new parcel at two units, ADUs included, so plan on 4 total |
| Lot split size | Each new parcel at least 1,200 sq ft, and neither parcel smaller than 40% of the original lot (the “60/40 rule”) |
| Unit size guarantee | City standards can’t block units of at least 800 sq ft |
| Setbacks | Cities can require no more than 4 ft side and rear setbacks. None for an existing structure, or one rebuilt in the same footprint |
| Parking | Up to 1 space per unit. None within a half mile of high-quality transit or a major transit stop |
| Owner occupancy | Lot splits only: an affidavit that you’ll live in one unit as your principal residence for 3 years |
| Rentals | Units must be rented for terms longer than 30 days (no short-term rentals) |
| Approval timeline | 60 days from a complete application, or it’s deemed approved (SB 450) |
The unit cap is the line that trips up most buyers. In Orange County, several cities count ADUs toward the two-unit limit on each split parcel. I explain it in the two-unit maximum per parcel that most people misread.
Which lots are excluded
A lot can sit in a single-family zone and still not qualify. Common deal-killers:
- Historic: a historic district, a property on the State Historic Resources Inventory or a local landmark
- Hazard areas: very high fire hazard severity zones (unless the site meets state fire-mitigation standards), flood zones, earthquake fault zones, wetlands and protected habitat
- Tenant history: you can’t demolish or alter housing that was occupied by a tenant in the last 3 years, or that is rent-controlled or deed-restricted affordable
- Ellis Act: a parcel where rentals were taken off the market under the Ellis Act in the last 15 years
- Repeat splits: a parcel created by a prior SB 9 split, or a split next to a parcel you (or someone working with you) already split
Private HOA CC&Rs can also restrict a project even when the city can’t. Check them before you write an offer.
What changed from 2024 to 2026
SB 450 (effective January 1, 2025)
SB 450 strengthened SB 9 for property owners. Cities now have 60 days to act on a complete application, can only apply standards that apply uniformly in the zone, and must put denials in writing with a list of fixes. It also removed a separate cap tied to demolishing more than 25% of exterior walls on tenant-occupied sites.
The charter-city lawsuit
In April 2024, an LA Superior Court judge ruled SB 9 unconstitutional as applied to five charter cities led by Redondo Beach (with Carson, Torrance and Whittier among them). On November 12, 2025, the Court of Appeal sent that ruling back to the trial court, holding that SB 450 is a change in law the judge has to consider. A separate challenge by general law cities was rejected in January 2025.
Bottom line as of October 2026: SB 9 is in effect across Orange County and LA County. The full court timeline is in Is SB 9 still valid in 2026?
Is SB 9 actually being used?
Slowly. In its first year, a UC Berkeley Terner Center review of 13 cities counted about 100 lot split applications and about 282 SB 9 unit applications, with the City of Los Angeles accounting for 211 of those units. The researchers pointed to construction costs, restrictive local ordinances and competition from easier ADU rules.
For investors, that’s the real takeaway. The law is the easy part. The lot, the build cost and the appraisal decide whether an SB 9 deal works. An SB 9 unit is not an ADU, and lenders and appraisers treat the two differently.
Go deeper: our full SB 9 guides
This page is the short version. When you’re ready for the details, start here:
- The full explainer: SB 9 Explained (2026 Update): turning a single-family lot into a duplex or two lots
- Orange County rules: SB9 in Orange County: lot splits and non-lot splits
- Long Beach: SB9 lot split in Long Beach (2026): which lots qualify and the numbers
- Financing: SB 9 lot split financing: what happens to your mortgage
- How much you can build: Lot coverage, multiple ADUs and the 800 sq ft rule
- Unit size vs. rent: Buena Park SB9 units: 500 vs. 800 sq ft and what each rents for
SB 9 FAQ
What is SB 9 in California?
A state law, effective January 1, 2022, that lets owners of most single-family lots build two homes or split the lot into two parcels with ministerial (no-hearing) approval.
How many units can you build under SB 9?
With a lot split, up to two units on each new parcel, so four total. Without a split, two primary units plus ADUs where ADU law allows. Local caps vary, so check the city’s ordinance.
Do I have to live on the property?
Only for a lot split. You sign an affidavit that you intend to live in one unit for at least three years. A two-unit development without a split has no state owner-occupancy rule.
What is the minimum lot size for an SB 9 lot split?
Each new parcel must be at least 1,200 sq ft, and the smaller parcel must be at least 40% of the original lot. A city can allow smaller lots by ordinance.
Is SB 9 still valid in 2026?
Yes. The 2024 charter-city ruling was sent back to the trial court in November 2025, and SB 450 strengthened the law starting in 2025.
Is an SB 9 unit the same as an ADU?
No. An SB 9 unit is a primary dwelling, and an ADU is accessory to one. They follow different size, fee and appraisal rules.
Talk through a specific lot
If you’re looking at a property and want to know whether SB 9, ADUs or both fit the lot, I’ll walk through the zoning, exclusions and numbers with you.
👉 Book a buyer ADU consult call to go through your options with Dylan
Prefer to talk now? Call Dylan Serna, ADU Realtor at 714-860-2868.
Dylan Serna | The ADU Realtor | eXp Realty | DRE #02217359. This post is general information, not legal advice. Confirm current rules with the city and a land use attorney before you buy.
