What S.F. could look like

Any attempt to add meaningful housing density will need to take a new approach

Lately, more places across the United States, such as Portland, Ore., and Minneapolis, have started allowing apartments to be built in areas that previously only allowed houses.

One of the most popular types of rezoning is one that allows for so-called “missing middle” housing — buildings that are larger than a house, but smaller than a five-story apartment block. In California, such efforts started with state and local laws to allow accessory dwelling units, such as garage conversions or backyard cottages, to be added to existing houses. Last year, SB9, introduced by state Sen. Toni Atkins, D-San Diego, passed the Legislature and was signed by Gov. Gavin Newsom. It took effect Jan 1 and allows up to four homes to be built on lots previously zoned for just one.

For a city with a limited amount of space like San Francisco, however, SB9, isn’t the most effective tool to add more housing. That’s because it was written with the typical California suburb in mind, which might have a 2,000-squarefoot house on a 5,000-square-foot lot — plenty of yard space that can be built on. San Francisco is different.

Not only are the lots smaller, but the land in San Francisco and the existing buildings on them are more expensive. There often isn’t room to build four detached houses on a single lot. And, even if there were, it would almost certainly require demolishing the existing building — a costly choice.

Any attempt to add meaningful density in the city’s single-family neighborhoods will need a different approach to making building apartments more attractive than the status quo of renovating and flipping old homes.

Let’s take a look at what that might look like for San Francisco’s three main types of houses: “Little Boxes,” the rowhouses on the west and south sides of the city; the mansions on large lots; and the older Victorians. Found throughout the Sunset, Excelsior, Bayview and Outer Richmond — as well as Daly City, where the song “Little Boxes” made them famous — they are San Francisco’s most common type of house. Your average Little Box was built from the 1920s to the 1960s and is a two-story building with a garage on the first floor and living space above, occupying the front half of what is typically a 25-foot wide, 100-foot deep, 2,500-square-foot lot. These homes sell for $1 million to $2 million, making most of them too expensive to tear down and build only four units of housing to replace them.

Developers in San Francisco, whether they’re building modest five-story apartments or 50-story towers, pay about $100,000 to $150,000 per unit. However, even houses that are fixeruppers are currently selling for over $1 million. That’s more than $250,000-perunit land cost if only four homes can be built.

For a Little Box lot selling for $1 million to $2 million to be an economically feasible development site, it needs to allow at least 10 units — in other words, a five-story or six-story building. Most Little Box neighborhoods already contain examples of mid-rise apartment buildings like this, especially on corner lots.

Another option for making Little Box redevelopment feasible would involve a hybrid renovation and new building strategy. In this scenario, the garage of an existing home could be converted into a second unit, while a third and fourth unit are built in the backyard.

Big mansions, such as those in Pacific Heights, offer large potential for creating economic growth and opportunities for a wider range of people to live near jobs and transit. The lots that host these homes are big — typically 50 feet wide by 100 feet deep. Accordingly, they are also much more expensive, selling for several million dollars. To be worth more as a development site than as a luxury mansion, zoning would likely need to allow for 40 or more apartments per lot. Again, the past hints at what’s possible. These neighborhoods feature many existing high-rises dotted among the mansions, including the ones at the top of the Lombard Street curves, along Green Street or the elegant 1920s apartment tower on Steiner Street that stands over Alta Vista Park in Pacific Heights.

Finally, there are Victorian houses.

Like the Little Boxes, these homes typically occupy 25-foot wide, 100-foot deep lots. However, the Victorians are much larger than Little Boxes — often 3½ stories tall. Many have historic value. But even those that don’t are likely too expensive to demolish for a development site anyway. Instead, Victorians would be good candidates for conversion into two-to-six-unit apartment buildings. Many, in fact, already are. Garages are an easy place to start. Changing the planning code to allow mid-rise apartment buildings with fire sprinklers to have a single stair —which Seattle does — would also allow the attics to become separate fourth-floor apartments.

Ending apartment bans is one part of solving the housing shortage. In addition to new homes in residential neighborhoods, we also need them in commercial zones, especially downtown. Other Bay Area cities also need to build, especially Silicon Valley cities with more jobs than homes. Stronger tenant protections can also keep existing residents housed while waiting for new homes to be built and steer investment into building new homes rather than flipping existing ones. Subsidized affordable housing and mixed-income social housing are needed for those that can’t afford new construction.

Together, these approaches have the potential to not only solve the housing shortage but also support local businesses, bring in new tax revenue to replace the losses from office vacancies and shorten commutes by making room for more people who work in the city to also live in the city.

Not only are the lots smaller, but the land in San Francisco and the existing buildings on them are more expensive.

Alfred Twu is an architect, artist and housing advocate who creates illustrations explaining state housing legislation. He also serves on the Berkeley Planning Commission and has been involved in the city’s General Plan Housing Element update.

Illustration by Alfred Twu / Special to The Chronicle An illustration of what San Francisco could look like if the city took ending single-family zoning seriously.

Carlos Avila Gonzalez / The Chronicle 2014 Victorian houses in San Francisco — like the tourist-favorite Painted Ladies — are larger, multistory homes and are good candidates for conversion into two-to-six-unit apartment buildings. Many, in fact, already are.