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California Senate Bill 9, effective January 1, 2022, created a ministerial right for homeowners in single-family residential zones to split their lots and build up to two units on each resulting parcel — potentially allowing four housing units on a lot previously limited to one. For California property owners, this law creates opportunities that are worth understanding, along with constraints and HOA complications that limit its practical scope.
What SB 9 Allows
SB 9 allows an owner of a single-family residential property to apply for: an urban lot split creating two parcels of roughly equal size (minimum 1,200 square feet each); the construction of one additional unit on each parcel under the Accessory Dwelling Unit (ADU) framework; and the conversion of the existing home into two units. The result: a single-family lot could theoretically support four housing units — the original home split into two, plus an ADU on each resulting parcel. Cities are required to ministerially approve SB 9 projects that meet basic eligibility requirements.
The HOA Complication
SB 9 explicitly does not override CC&R provisions that prohibit lot splits or multi-unit development. If your property is subject to an HOA with CC&Rs that limit density or prohibit lot splits, SB 9’s city-level authorization doesn’t override the HOA restriction. This is the most significant practical limitation on SB 9’s impact in HOA communities — which cover a substantial portion of California’s single-family residential stock. Before pursuing an SB 9 project, review your CC&Rs carefully for density restrictions, lot coverage limitations, and any provisions that could be interpreted to prohibit or restrict the project.
The Investment Thesis
For investors who own or are considering acquiring single-family properties without HOA restrictions in appropriate locations, SB 9’s lot split right creates a potential value unlock that the original purchase didn’t price in. A $800,000 single-family lot in a desirable area that can be split into two parcels — each supporting a duplex — potentially has development value significantly above its current use value. The analysis requires attention to SB 9’s specific eligibility requirements, local implementation ordinances, and the economics of the specific project. The opportunity is real but property-specific.
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