California (statewide): Senate Bill 9 (California HOME Act)

For most of the last century, the majority of residential land in California's cities was reserved by law for one detached house per lot. That single-family-only rule kept neighbourhoods low-density even as the state's population grew and home prices climbed out of reach for ordinary buyers and renters. By the early 2020s, the gap between how many homes California needed and how many it was building had become one of the defining political problems in the state.

Senate Bill 9, formally the California Housing Opportunity and More Efficiency (HOME) Act, was the Legislature's attempt to break that pattern at the level of the individual lot. Governor Gavin Newsom signed it on September 16, 2021, and it took effect on January 1, 2022 (Holland & Knight). The idea was simple to state and explosive to pass: end the rule that a single-family lot can hold only one home, and let owners add a second home or split the lot in two. Supporters called it the end of single-family-only zoning across the state. Opponents, including many city governments, saw it as Sacramento overriding decisions that local councils had always made. That tension over who controls land use, the state or the city, runs through everything that happened to SB 9 afterward.

SB 9 created two separate rights for the owner of a single-family lot in a single-family zone, and they can be combined. The first is the right to build a second home, turning the lot into a duplex. The second is the right to split the lot into two parcels, each of which must generally be at least 1,200 square feet (California Legislature). Each new parcel can then itself hold up to two units. So an owner who both splits the lot and builds a duplex on each new parcel can end up with as many as four homes where one stood before (Holland & Knight). The "four units" figure that gets quoted is this math: two parcels times two units each.

The most important word in the law is ministerial. A qualifying SB 9 project gets ministerial approval, meaning the city must approve it if it meets the written rules. There is no public hearing, no discretionary review, and no chance for neighbours to lobby the council to kill it (Holland & Knight). In exchange for that streamlined path, the law attaches a condition to lot splits: the applicant must sign an affidavit promising to live in one of the units as their principal residence for at least three years (California Legislature). That owner-occupancy rule was meant to keep speculators from buying up lots purely to subdivide and flip them, but it also turned out to be one of the law's biggest brakes on use, because it rules out most investors and many owners who do not want to commit to staying put.

SB 9 also does not apply everywhere. The law excludes land in a historic district or designated as a historic property, very high fire hazard severity zones, special flood hazard areas and floodways, delineated earthquake fault zones, prime farmland and farmland of statewide importance, wetlands, hazardous waste sites, and protected habitat or conservation lands (Holland & Knight). In a state with as much wildfire and flood exposure as California, those carve-outs remove a meaningful share of lots before an owner ever fills out a form.

This is the part of the SB 9 story that matters most, and it is a cautionary one. Before the law passed, the Terner Center for Housing Innovation at UC Berkeley ran the numbers and estimated that SB 9 could make roughly 700,000 new homes newly feasible to build across California (Terner Center). That headline number was widely repeated. What got repeated far less often was the Terner Center's own warning attached to it: the researchers said it was unlikely that anywhere near 700,000 homes would actually be built, because homeowners face high construction costs, financing hurdles, and a simple lack of experience with home building (Terner Center). "Feasible" was always a ceiling, not a forecast.

The real-world numbers came in far below even modest expectations. In the law's first year, the Terner Center tracked applications in California's largest cities. Through November 2022, Los Angeles, the most active city, had received just 28 lot-split applications and 211 applications for new units, and had approved only 38 of those units while approving zero lot splits (Terner Center). San Diego was even quieter: it received just 7 SB 9 applications in a year when it issued more than 5,000 housing permits and 871 accessory dwelling units (Terner Center). A separate review of 13 municipalities found that eight of them, including Anaheim, Bakersfield, Berkeley, Long Beach, San Diego, and San José, did not approve a single SB 9 unit in 2022 at all (California YIMBY).

The numbers did not improve much. By 2023, building permits for only 140 units statewide were issued under SB 9 (CalMatters). For a law projected to unlock hundreds of thousands of homes, a few hundred units across the entire state is, in plain terms, almost nothing. The reasons are practical. The owner-occupancy rule shuts out investors. Rising interest rates and high construction costs hit small projects hard (Terner Center). And many cities layered on their own restrictive rules, such as low height limits and large setbacks, that shrank what could actually be built; a Terner Center review found six of ten cities studied imposed height limits under 20 feet on SB 9 projects (Terner Center). Each rule on its own is small. Stacked together, they made the math not work.

While uptake stayed low, a fight over whether the law could even be enforced played out in court. California has two kinds of cities. "Charter cities" have their own local constitutions and, under a doctrine called "municipal affairs," some protection from state interference in purely local matters. "General law cities" do not. Several charter cities seized on that distinction to argue that Sacramento could not force SB 9 on them.

Five charter cities, Redondo Beach, Carson, Torrance, Whittier, and Del Mar, brought the lead case. On April 22, 2024, a Los Angeles County Superior Court judge ruled in their favour, finding that SB 9 was not reasonably related to ensuring affordable housing and could not be enforced against charter cities (Allen Matkins). The state appealed. On June 21, 2024, Attorney General Rob Bonta filed a notice of appeal to overturn the decision that barred enforcement against the five cities (California Attorney General).

While that appeal was pending, the Legislature changed the law underneath it. It passed Senate Bill 450, signed on September 19, 2024 and effective January 1, 2025, which amended SB 9, curtailed how far cities could restrict these projects, and reinforced that the law applies to charter cities as a matter of statewide concern (Burke, Williams & Sorensen). Because the trial court's ruling had relied on language SB 450 rewrote, the Court of Appeal reversed and remanded the charter-cities case on November 12, 2025, sending it back to the lower court to reconsider under the new statute. In a parallel 2025 case, City of Rancho Palos Verdes v. State, the Court of Appeal held that general law cities cannot invoke the municipal affairs doctrine at all and must comply with SB 9 (Holland & Knight). The bottom line: SB 9 remains in force across California, charter cities included.

The single clearest lesson from SB 9 is the distance between a spreadsheet and a finished building. The 700,000 figure described what would pencil out on paper if owners chose to act, financing were available, and construction costs cooperated (Terner Center). None of those conditions are automatic. A homeowner has to want a second unit, have the cash or credit to build it, find a contractor, clear the city's rules, and accept the three-year residency commitment for a lot split. Every one of those steps is a point where an otherwise "feasible" project quietly dies.

The contrast with accessory dwelling units makes the point unmistakable. Over the same stretch that SB 9 produced 140 permitted units in 2023, California permitted more than 28,000 ADUs in that single year (CalMatters). In Los Angeles alone, the city permitted 5,064 ADUs in 2021, compared with the 38 SB 9 units it approved in 2022 (California YIMBY). Both are state laws aimed at adding homes on single-family lots. The difference is friction. ADU rules were steadily simplified, fees were capped, and there is no owner-occupancy requirement, so owners actually used them. SB 9 kept the harder conditions, and owners mostly walked away. Same goal, opposite result, decided almost entirely by how much hassle the law left in place.

British Columbia took a different road to a similar destination, and the contrast is instructive for anyone weighing what these laws do. California's SB 9 is permissive: it gives individual owners the option to build a duplex or split a lot, then leaves the decision, the financing, and the construction entirely to them. The result, as the numbers show, was that most owners did not act.

BC's Bill 44, the Small-Scale Multi-Unit Housing (SSMUH) legislation passed in late 2023, works through the city rather than the individual. It requires municipalities to rezone single-family lots to allow multiple units by right, with a hard minimum: typically at least three or four units on a standard lot, and up to six units on larger lots near frequent transit. Cities had to update their bylaws to comply, not simply allow owners to ask. In other words, where SB 9 dangled an option and waited, Bill 44 changed the baseline zoning across whole cities and set a floor that local councils could not drop below. Whether that produces far more homes than SB 9 will take years of data to judge, but the design philosophy is the opposite: BC tried to reduce the number of decisions standing between zoning and a built home, which is exactly the friction that strangled SB 9.

The practical takeaway from California is short and worth keeping in front of mind: permission is not production. SB 9 gave hundreds of thousands of California owners the legal right to add homes, and after two full years the state had permitted only a few hundred units under it (CalMatters). A zoning law that lets you build something is not the same as a project that makes money once you account for construction costs, financing, fees, and the local rules layered on top.

For a BC owner or builder looking at a multiplex under SSMUH, the discipline is the same as it would have been in California. Before spending real money, run the actual numbers for your specific lot: what the city's objective rules let you build, what it will cost to build it, what the units will rent or sell for, and what financing is available at today's rates. The California experience shows that the gap between a law allowing four units and a real project that pencils out can be enormous. Treat the zoning right as the starting point, not the answer, and verify the math before committing, because the property's zoning is only the permission; the deal is what makes it real.