San Francisco is loosening a little-known building rule that housing advocates have long blamed for making small apartment buildings hard to pencil out. Mayor Daniel Lurie and the Department of Building Inspection are issuing new rules Friday that relax the requirement that buildings of three or more stories have two interior stairways, the San Francisco Chronicle reported.
What changes
Under the new rules, a four-story building can have one primary interior stair plus a secondary way out, such as a fire escape or an exterior staircase. Five- and six-story apartment buildings can pair one interior stairway with an exterior stairway instead of building a second one inside. Buildings taller than six stories still need two stairways, according to the Chronicle.
The change is not automatic. Builders must submit a single-stair proposal that the Department of Building Inspection has to approve, and they can appeal if a project is turned down. Hoodline noted that this makes it a case-by-case option rather than a guarantee for any given lot.
Why it matters for small lots
Developers say fitting two interior stairs and the hallway connecting them onto a narrow or oddly shaped city lot eats up floor space and money. The target is the small four- to six-unit buildings on mid-block lots that advocates call "missing middle" housing. A Pew Charitable Trusts analysis cited by Hoodline estimated that small single-stair buildings cost 6% to 13% less to build than comparable two-stair designs, and that the second stair and corridor can take up roughly 7% of usable floor area. Those are general estimates, not a figure for any specific San Francisco project.
Safety is the main question critics raise. Pew's research looked at modern single-stair buildings in New York City and Seattle and found four fire-related deaths in them from 2012 through 2024, with New York's fire-death rate in those buildings no different from other residential buildings. At the state level, a separate fire-safety report has recommended a four-story cap with extra safeguards, Hoodline reported, but that does not govern the city's new local rules.
The bigger push
The change fits Lurie's broader effort to make building faster and cheaper, which has included cutting fees and affordable-housing requirements, streamlining approvals and allowing more height and density through his "Family Zoning" plan. The Chronicle reported that only one market-rate project is under construction in the city while rents climb sharply in some neighborhoods.
"For years, San Francisco made it easier to block housing than build it," Lurie said in a statement. San Francisco is the second California city to adopt single-stair reform, after Culver City; Los Angeles is drafting its own plan.