Three California laws let a homeowner put more than one home on land that used to hold one. They get discussed as if they were interchangeable. They are not, and choosing the wrong one costs months.
Here is the short version, then the detail.
The short answer
SB 9 splits one single-family lot into two, with up to two units on each — four homes maximum. It works on lots that already have a house on them.
SB 684 and SB 1123 go much further — up to ten lots and ten homes — but the single-family track requires the lot to be vacant, and caps average unit size at 1,200 square feet.
So the first question is not which law is better. It is whether your lot has a house on it.
SB 9: the two-into-four path
SB 9 has been in effect since 2022 and is the one most Los Angeles homeowners have heard of. It allows an urban lot split of a single-family parcel into two, with resulting parcels no smaller than 1,200 square feet, and permits up to two units on each — four homes where one stood.
Its advantage is that it works on an improved lot. You do not have to demolish first, and you do not have to start with raw land. Its limits are equally clear: the ceiling is four units, the split itself carries an owner-occupancy commitment, and the two resulting parcels have to be reasonably balanced rather than one large and one token.
For most Los Angeles homeowners sitting on a standard lot with a house on it, SB 9 is the only one of the three that applies at all.
SB 684 and SB 1123: the ten-unit path
SB 684 passed in 2023 and applied to multifamily-zoned land. SB 1123 amended it in 2024 to extend the same streamlined route to vacant single-family lots. Together with AB 130 they took effect on 1 July 2025, and they are treated as one programme in practice.
Both tracks cap the project at ten parcels and ten units on an urban infill site under five acres that is substantially surrounded by existing development. Past that, the zoning decides:
- Single-family zones — the lot must be vacant and no larger than 1.5 acres. Resulting parcels at least 1,200 square feet. Average unit size across the whole project capped at 1,200 square feet.
- Multifamily zones — up to five acres, resulting parcels at least 600 square feet, average unit size capped at 1,750 square feet.
Both allow one off-street parking space per unit, uncovered and unenclosed. That sounds minor and is not: it frees the site plan from structured parking, which is often what makes a small-lot project pencil at all.
Which one applies to your lot
Work through it in this order.
Is the lot vacant? If yes, and it is under 1.5 acres in a single-family zone, SB 684/1123 is available and you are looking at a potential ten-unit project rather than four. If no, that track is closed and SB 9 is your route.
Is the lot zoned multifamily? Then the vacancy requirement does not bind you the same way, the site can run to five acres, and the average unit cap rises to 1,750 square feet — a materially different building.
Is the site genuinely urban infill? All three assume a lot surrounded by existing development. Fringe parcels and undeveloped edges generally fail this test regardless of size or zoning.
What none of them fix
Every one of these laws removes discretion. None of them removes cost, and that is where most projects actually fail.
The 1,200 square-foot average on the single-family track is the constraint people underestimate most. It is an average across the project, so one larger home forces the rest smaller. Ten units at that average is a fundamentally different product from the houses selling around it, and it has to be underwritten against that market rather than the one next door.
Then there is the arithmetic nobody enjoys: ten resulting parcels carry ten sets of service connections, frontage obligations and closings. Per-unit soft costs on a ten-lot split do not divide the way they do on a single residence. And in Los Angeles, topography decides more outcomes than zoning does — a hillside parcel that clears the statute on paper can still fail on grading, access and caisson cost.
Ministerial approval is a checklist with a clock on it. It is not a shortcut.
Before you commit
The screen above will tell you which law is even in play. Whether the resulting project is worth building is a separate question, and it is the one worth answering first — before design fees, before a surveyor, and certainly before demolition, since demolishing to create a vacant lot does not work the way people assume.
We run that screen on parcels across Los Angeles. Send an address and we will tell you plainly which track applies and whether the numbers support it — including when they do not.
Summarized from the statutes as amended and in effect. Eligibility turns on the specific parcel, its zoning and current city or county interpretation. This is a screen, not a legal opinion, and it is not a substitute for counsel.