What SB 9 actually allows
Senate Bill 9, in effect since January 2022, lets eligible California homeowners do one or both of the following on a single-family-zoned lot:
- Lot split: Divide one lot into two roughly equal lots.
- Two-unit development: Build up to two primary units on each lot.
If you do both, you can end up with up to four total units (two per lot) on what used to be one single-family parcel.
Who qualifies
To use SB 9 your lot must be:
- Zoned single-family residential.
- Not in a historic district or designated hazard zone (fire, flood, earthquake).
- Located in an urbanized area.
You also must commit to live on the property for three years after a lot split.
How SB 9 overlaps with ADU law
SB 9 is separate from ADU law, but they interact. On a single-family lot, you generally have two stacking paths:
- ADU + JADU: Add one ADU and one Junior ADU under existing ADU law.
- SB 9 two-unit: Add a second primary unit under SB 9.
In some scenarios you can combine them. Your city ultimately decides whether SB 9 units count separately from ADUs. Local zoning still applies for setbacks, height, and parking.
What SB 9 cannot do
- Cannot force a city to ignore historic preservation overlays.
- Cannot bypass the Coastal Commission in coastal zones.
- Cannot increase total units beyond what local zoning, ADU law, and SB 9 jointly allow.
Should you use SB 9 or build an ADU?
For most Southern California homeowners, an ADU is faster, cheaper, and less legally complex than an SB 9 lot split. SB 9 makes the most sense when:
- You want to sell one of the two units separately.
- Your lot is large enough that a clean split produces two viable building sites.
- You are working with an experienced land-use attorney.
For everyone else, the standard ADU path is usually the better move.
Related reading
- AB 1033 California: selling ADUs as condos
- Detached vs attached ADU
- ADU permit guide for Los Angeles
- Vision ADU Service Areas
Frequently asked questions
Can I split my lot under SB 9 and immediately sell one half? You must commit to living on the property for three years before any sale.
Does SB 9 override HOA rules? No. HOA restrictions can still block SB 9 development.
Are SB 9 projects ministerial? Yes — cities must approve them ministerially if they meet objective standards.