SB9 — plus two associated bills, SB8 and SB10 — will not end single-family zoning in California, though. While SB9 will allow a lot of single-family homes to be converted, it actually doesn’t apply to millions of homes — including residences in rural areas, high fire-risk zones and historical districts and on lots smaller than 2,400 square feet.
Before SB9 passed, the Terner Center for Housing Innovation at UC Berkeley published a report looking at how many new homes it could help California produce. The center’s staff first analyzed how many of California’s 7.5 million single-family homes would be eligible for lot-splitting. They then looked at how many of those lots would actually make sense to split, financially speaking. The goal was to get an idea of how many new homes might actually get built thanks to SB9, not just how many were technically made legal by the new bill.
The Terner Center found that SB9 will make 700,000 new units “market-feasible” — a decent number of new homes, but not enough to address a shortage of nearly 2 million units statewide. If all 700,000 units were built, that would increase the number of housing units in the state by 5%.
The report also broke down the number of possible new housing units by county. The Chronicle looked at how those numbers stacked up to each county’s current housing supply and population to see which counties stand to gain the most housing.
We found that SB9 would have an uneven effect across the Bay Area. In counties like Napa, Sonoma and Marin, which tend to have more suburban neighborhoods and homes with larger lot sizes, the bill could add up to 36 new homes per 1,000 residents.
However, the bill will have less of an effect in counties with denser neighborhoods, like San Francisco and Alameda. In San Francisco, the center estimated that SB9 could only increase housing supply by 8,500 units, a 2% increase on the number of current units. That’s largely because the city’s neighborhoods consist of small homes on small lots, David Garcia, policy director at the Terner Center, told The Chronicle
“Parcel size is actually a significant indicator of whether or not any new development would be feasible under SB9,” Garcia said. “In older neighborhoods like what you see in San Francisco, the parcels are going to be relatively small.”
Garcia said that it’s likely the bill’s impact on California’s housing shortage will be “modest,” especially at first. For one, it’s unlikely most of the 700,000 feasible units will get built right away, or ever, he said.
“It’s really incumbent upon the homeowner to do this,” he said. He added that it’s likely new units will be concentrated in wealthier neighborhoods, because landowners there can afford to subdivide their homes and housing costs are high enough that it makes financial sense to do so.
Additionally, cities can impose their own requirements on top of SB9, like height restrictions on new construction or charging impact fees, he said.
But SB9 isn’t meant to radically increase California housing stock overnight, Garcia said. Rather, it’s meant to “set the table for modest increases in neighborhood density over a period of time.”
Susie Neilson is a San Francisco Chronicle staff writer. Email: firstname.lastname@example.org Twitter: @susieneilson