SB 9, the “California HOME Act” (Chapter 162, Statutes of 2021), took effect on January 1, 2022. In plain terms, it did two things to parcels in single-family residential zones: it made a second unit possible on many of them, and it allowed a one-time lot split — both with ministerial approval, meaning no discretionary hearing if the project meets objective standards.
The two mechanics live in different Government Code sections: § 65852.21 governs two-unit developments, and § 66411.7 governs urban lot splits. Combine them and you get the widely repeated “up to four units” headline — but the details decide whether any given lot qualifies.
The two-unit path
On a qualifying single-family parcel, SB 9 requires a city to approve a housing development of up to two units ministerially. That can mean adding one new unit to an existing house, or building two new units. Because approval is ministerial, CEQA does not apply to the decision.
The lot-split path
Separately, SB 9 lets an owner split one parcel into two. The statute sets real guardrails:
- Two parcels of roughly equal size — neither smaller than 40% of the original lot, and neither smaller than 1,200 square feet.
- A three-year residency pledge. The applicant must sign an affidavit stating they intend to occupy one of the units as their principal residence for at least three years (community land trusts and qualified nonprofits are exempt).
- Each new parcel can then host up to two units — which is how a single original lot can reach up to four homes.
Where SB 9 does not apply
SB 9 has meaningful exclusions. It generally cannot be used where it would require demolishing or altering:
- Housing subject to a recorded affordability covenant or rent/price control;
- Housing that has been occupied by a tenant in the last three years;
- Property in a historic district or on a historic register, and land in certain hazard categories such as very high fire severity zones, prime farmland, or protected habitat.
That caveat is the whole reason parcel-level, jurisdiction-specific answers matter. “Does SB 9 apply to me?” depends on your city’s charter status, your zone, your lot’s hazard overlays, and its tenancy history — a stack of facts no generic summary can resolve for a single address.