Scott Wiener, the San Francisco-based California state senator hellbent on clearing away restrictive zoning across the state, failed to create great swaths of multi-unit housing near transit and job centers earlier this year when his SB 50 bill died on the senate floor. Now he’s thinking smaller with new legislation focused on two- to four-unit homes.

The latest Wiener working, SB 902, would radically change zoning standards across the entire state by eliminating local housing rules that limit parcels to just one home. In cities like San Francisco, it would also knock down standards that bar three- or four-unit homes in many neighborhoods.

But the increase in density would still be slight compared to previous, more aggressive efforts: small towns and suburbs (up to 10,000 people) could still limit parcels to two units, midsize cities (up to 50,000 people) to three units, and big cities (anything large than 50,000) up to four units.

How many homes get built on upzoned land would be up to the property owners, but no longer would a quilt of local laws hold entire blocks or neighborhoods down to only one house at a time.

In San Francisco the change would be particularly dramatic where roughly 38 percent of developable lots in the city are zoned for one home at most (i.e., RH-1). Although note that in recent years the city eased restrictions far enough to allow in-law units on such properties.

SF lots marked RH-2 and RH-3 are about 21 percent combined. Homeowners and developers can attempt to build up properties beyond their default zoning, but only if the city agrees to waive the rules on a case-by-case basis. If Wiener pushes through his new plan, those parcels would get an upzone to potential quadplexes.

The fact that multiple homes on a property are illegal across so much of San Francisco remains a constant source of irritation for housing activists. YIMBY Action board member Steven Buss said in August, “The only housing rules guaranteed by law are what you can’t do,” calling citywide prohibitions on more ambitious development a scourge.

Academic research supports the idea that austere zoning limits are bad for the housing crisis. Washington DC-based think tank Niskanen Center claimed in 2018 that for cities like SF and San Jose strict zoning regulations drive up home prices so much they may be responsible for as much as half the cost of housing.

Last year, UCLA researchers concluded that California can’t build enough housing to match demand as it stands now, calculating that the Bay Area will soon hold 20 percent of the state’s population but is only zoned for enough housing for 13 percent.

Nevertheless, single-family zoning has its defenders. When Seattle pared back zoning barriers across neighborhoods in 2019, protesting residents predicted “pollution, impairment, or destruction of the air, water, land or other natural resources” from new construction. And Yonah Freemark, a PhD candidate at the Massachusetts Institute of Technology, concluded that upzoning changes in Chicago weren’t enough to spur significant development in many neighborhoods.

Those proposals all called for much greater increases in potential housing volume than Wiener’s plan. The state senator hopes that the “light touch” of SB 902 will make it more palatable to some of the interests that stonewalled his previous build-up efforts.

But a lot of local governments—including San Francisco, where Wieners’s onetime Board of Supervisor colleagues repeatedly pilloried SB 50—resent any attempt by Sacramento lawmakers to intervene with local housing rules. His new bid could face familiar criticism.