San Francisco is allowing some four- to six-story apartment buildings to use one interior staircase alongside a secondary exit, rather than requiring two interior stairways. The local change is aimed at small, mid-block projects, but it does not create automatic approval for every site: proposals must be reviewed by the Department of Building Inspection, and applicants can appeal a rejection, the San Francisco Chronicle reports.
A limited option, not a parcel-by-parcel guarantee
Under the new approach, a four-story building may have one primary interior stair and a secondary exit, such as a fire escape or exterior stair. Five- and six-story buildings may pair an interior stair with an exterior stair; buildings taller than six stories still require two stairways, according to the Chronicle. The policy is intended for so-called “mission middle” developments—four- or six-unit apartments on mid-block lots. The paper reports that fitting two interior stairs on small or irregular sites can constrain apartment layouts and reduce usable floor area.
The Family Zoning Plan focuses zoning changes on major transit routes, commercial streets, major thoroughfares and activity hubs, according to San Francisco Planning.
Cost and safety evidence answer different questions
A Pew Charitable Trusts analysis estimates that small-floor-plate single-stair buildings cost 6% to 13% less to construct than comparable dual-stair buildings, and that a second stairway and its connecting corridor can take up roughly 7% of usable floor area. Those estimates describe potential design and cost effects; they do not establish how much a particular San Francisco project would save.
Pew’s safety findings are specific to modern single-stair buildings in New York City and Seattle: the study found four fire-related deaths in those buildings from 2012 through 2024. In New York City, the fire-death rate in single-stair buildings was no different from that in other residential buildings over that period. The findings offer evidence from those cities, not a forecast of safety outcomes under San Francisco’s rules.
Other rules show why local details matter
Single-stair policies vary in their limits. Portland’s Building Code Guide 25-10, implemented October 22, 2025, allows certain single-stair apartment buildings up to four stories, subject to conditions including a 4,000-square-foot limit per story and no more than four dwelling units on each story, according to Portland.gov. It is a useful example of a conditional allowance, but not a direct match for San Francisco’s five- and six-story option.
The state-level discussion is separate from San Francisco’s local policy. LAist reports that California’s fire-safety report recommended a four-story cap with additional safeguards if state lawmakers change the law, and advised against considering a six-story limit without another fire marshal study. Those recommendations do not set the rules for the city’s project-by-project review.
San Francisco’s change therefore creates a route for some small apartment proposals that previously faced a two-interior-stair requirement, while leaving both site eligibility and approval unresolved until individual applications are reviewed. The citywide zoning map, cost estimates from other small-lot projects and safety findings from other jurisdictions provide context, but none determines whether a specific San Francisco building will qualify or how it will perform.
