These charts present what kinds of houses exist in San Francisco and what’s getting constructed

Last week, Governor Gavin Newsom signed two major housing laws. The bill is designed to help alleviate the extreme housing shortage in California by increasing density across the country. One of the bills, SB9, will allow the division of land and duplex construction on most of the land designated for single family use. The other, SB10, will streamline the construction of buildings of up to 10 units near major transportation hubs.

Now that they’re in law, it’s worth looking at what the current Bay Area housing landscape is like, and how the bills could change that.

The American Housing Survey (AHS) collects data on the “housing mix” – the types of residential buildings in a city, such as semi-detached houses and single-family houses – in the 15 largest metropolitan areas in the USA. The Chronicle analyzed this data, collected in 2019, to see how the housing mix in the metropolitan area of ​​San Francisco compares to other major regions. (Greater San Francisco also covers much of the East Bay, including Oakland and Hayward.)

AHS data shows that the metropolitan area of ​​San Francisco has a relatively balanced mix of housing types compared to other cities. It has a smaller section of 2-4 units than any major metropolitan area except Boston; otherwise it is in the middle range of large cities for most building types.

At nearly 60% of all housing units, San Francisco has relatively fewer single-family homes (tied or free) in the housing stock than the average large subway, which is 66%. However, San Francisco is also the second largest metropolitan area in the country after New York – which had the lowest proportion of single-family homes of any metropolitan area in the survey.

Rich Hillis, director of the San Francisco Planning Department, said he believes SB 9 and 10 will help the city take some of these single-family homes, or at least their lots, and convert them into mid-range residential buildings – “the two” plexes, the three-plex, the fourplex buildings that are kind of the workhorse of the San Francisco housing stock, ”he said. Such buildings are commonly referred to as the “missing center” of urban housing; they add density to neighborhoods without building the high-rise towers that parishioners often object to.

Most of the units built in the past decade have been in such tall skyscrapers, especially in the east of the city, Hillis said. From 2011 to 2020, the number of new residential units in buildings with 20 or more units in the city rose by 31%, according to the planning office. In the same period, the number of residential units in buildings with 2-19 units increased by only 1.3%.

“I think [SB 9 and 10] will be effective, ”said Hillis. “That’s not the panacea either, but they add other tools to our toolbox to take account of the fact that we have not created enough housing over the past thirty years, particularly in the west of the city.”

Hillis said SB 10 in particular could help streamline the approvals of laws proposed by Supervisor Rafael Mandelman that would allow up to four residential units on any property designated for residential use in the city.

Hillis noted that SB9 alone is unlikely to seriously affect San Francisco’s housing shortage because so many of the city’s single-family lots are either too small or lacking enough front-facing land or “facade”. , split up. A recent study by the UC Berkeley Terner Center confirms it. The study found that SB9 could only add about 8,500 units, or just 2%, to San Francisco housing supply.

However, SB9 could actually have a significant impact across the Bay Area, enabling nearly 170,000 new housing units in the nine-county area, according to the Terner Center report.

Susie Neilson is a contributor to the San Francisco Chronicle. Email: susie.neilson@sfchronicle.com Twitter: @susieneilson