The short answer
SB 9 lets owners in single-family zones build two homes on a lot, and split the lot in two, with ministerial approval: up to four homes where there was one. It has tighter eligibility than ADU law (no historic properties, nothing that tears down or alters recently rented housing, one split only), and a lot split requires the owner to intend to live on the property for three years. For most homeowners, an ADU is the simpler path.
What it allows
- Two homes on a single-family lot, approved ministerially (Government Code § 65852.21).
- An urban lot split into two lots of roughly equal size, neither under 40% of the original and each at least 1,200 square feet unless the city allows smaller (§ 66411.7).
- Cities can't block two homes of at least 800 square feet each, require side and rear setbacks over 4 feet, or require more than one parking space per home (none near high-quality transit or a car-share vehicle). Rentals must be longer than 30 days.
- A complete application, for two homes or a split, is decided within 60 days or deemed approved.
Which lots don't qualify
- Projects that would demolish or alter housing under rent or price control, with an affordability covenant, or occupied by a tenant in the last three years; lots where an Ellis Act withdrawal happened in the last 15 years.
- Historic district contributors and landmark properties.
- Sites excluded by the state's streamlining rules (§ 65913.4), such as prime farmland, wetlands and some hazard zones, unless they meet that section's conditions.
- A lot created by an earlier SB 9 split, or one next to a lot the same owner already split.
How SB 9 and ADUs fit together
- After a lot split, a city doesn't have to allow more than two units on each new lot, counting ADUs and junior ADUs: four homes in all (§ 66411.7(j)).
- If a lot is split and built with two homes under SB 9, the city needn't allow ADUs on it (§ 65852.21(f)).
- Without a split, the state says a lot can have two SB 9 homes plus its usual ADU allowance (ADU Handbook); see California ADU rules.
SB 9 in Los Angeles
- The Department of Building and Safety handles two-home projects; City Planning handles lot splits.
- Eligible zones include RA, RE, RS, R1, RU, RZ and RW; historic preservation overlay zones (HPOZs) are excluded. ZIMAS has an SB 9 eligibility checklist for each parcel.
- SB 9 homes pay the city's park and affordable housing linkage fees, which ADUs don't, as well as LAUSD school fees (which ADUs over 500 square feet also pay).
- The city's SB 9 page lists its requirements; where it differs from the current statute (it still mentions an old limit on demolishing exterior walls), the statute controls.
In Ventura County, ask your city's planning department; each city handles its own SB 9 applications.
General information, not legal advice. SB 9 rules are detailed and lot-specific; talk to the city and a land-use professional before you plan a split.
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General information, not legal, zoning or financial advice. Rules change
and depend on your lot; check with your city before you design or build.