San Francisco housing advocates say Mayor Daniel Lurie’s proposed building-code changes do not deliver the single-stairway reform they have sought to make new housing easier to build. The changes would allow some buildings to use one interior staircase, but only if they also include a fire escape or exterior stairway. For five- and six-story buildings, the proposal would require a second exterior stair. Advocates say those conditions leave in place much of the design and space burden that a second staircase creates. Lurie’s office developed the revisions with Fire Marshal Chad Law and David Kane, interim director of the Department of Building Inspection. The department said the changes offer another tool for building more housing. The mayor’s office did not respond to a request for comment. The proposal was scheduled for discussion Wednesday by the city’s Code Advisory Committee. The committee can offer recommendations but cannot approve or change the rules. The changes can take effect after sign-off by Law and Kane, who could still revise them; they do not require approval from the Building Inspection Commission, Planning Commission or Board of Supervisors. Brandon Powell, organizing director for YIMBY Action, said the proposal was not the broader reform advocates had expected. A single interior stair, he said, can free up space for larger units and more flexible layouts, as well as improve access to light and air. Those design changes can also reduce the portion of a building that does not generate rental income, he said, helping projects become financially viable. Powell said advocates were surprised by the announcement and would have urged the mayor not to describe the proposal as single-stair reform. Supervisor Myrna Melgar, who had put her own legislation on hold while the administration worked on the issue, said she plans to introduce a bill allowing one stairway in all four-story buildings without requiring a fire escape or exterior stair. She characterized the mayor’s changes as a clarification of existing rules. Melgar pointed to Seattle as a model for allowing a single stair in four-story buildings. Seattle and New York also permit single-stair designs in five- and six-story buildings under conditions that include two-hour fire-resistance ratings for the stairs. Architect Mark Hogan, who has advocated for the change in San Francisco for more than a decade, said the next cycle of international building codes, expected to take effect in 2027, will allow single stairways in four-story buildings without an additional fire escape or exterior stair. Those codes serve as a template for state and local rules, though jurisdictions can adopt amendments. Chris Elmendorf, a UC Davis law professor who studies California housing law, said the change is particularly significant in San Francisco, where narrow lots can leave little room for a second staircase. On a 25-foot-wide lot, he said, adding another stair can take up space that could otherwise be used for housing or windows. The debate comes as rents have risen sharply in some San Francisco neighborhoods and the city struggles to restart market-rate construction after a pandemic-era slowdown. One market-rate project is under construction, while several others are expected to begin in the coming months, according to the information provided by city housing advocates. Corey Smith, executive director of the Housing Action Coalition, said the group does not consider the mayor’s proposal single-stair reform. He said broader changes are needed to support housing construction in neighborhoods including the Sunset and Richmond, while recognizing that fire safety concerns are central to the debate. Smith also argued that new buildings can improve safety because they must meet current fire standards, including sprinkler requirements that many older buildings do not meet. The challenge, he said, is balancing those protections with rules that allow more housing to be built.