The deceptively simple reform that could unlock more housing

This story was originally published in The Highlight, Vox’s member-exclusive magazine. To get early access to member-exclusive stories every month, join the Vox Membership program today. Michael Eliason was an undergraduate studying architecture at Virginia Tech University when he went to live for a year in Germany. While interning in Freiburg in 2003, he worked on projects including apartment buildings four or five stories tall. After returning to the US and graduating, Eliason began his architecture career in Seattle, where he soon noticed that all the buildings he worked on kept getting “bigger and bigger.” It felt to him “like the exact opposite of my experience working in Germany.” Reviewing his portfolio years later, Eliason noticed a stark contrast: All the US apartment buildings were massive and deep, while the European ones were relatively thin, featured different unit layout sizes, and welcomed significantly more natural light. He couldn’t quite articulate the significance yet, but he began to recognize that the German approach seemed to be the standard for urban housing throughout Europe, South America, and Asia. [Image: Michael Eliason https://platform.vox.com/wp-content/uploads/sites/2/2025/04/eliason_headshot_8adfea.jpg?quality=90&strip=all] In 2019, Eliason moved back to Germany with his wife and children. Before the first day at his new job, he and his soon-to-be boss discussed a 12-story housing project that had recently won a competition. Eliason was confused by the blueprint. “There needs to be a second stair, right?” he asked. “Because in the US we would require a second stair for anything over three stories.” His new employer was puzzled by the question and explained that adding a second staircase would make the project financially infeasible. “That was really the turning point for me,” Eliason told Vox. “The realization that the way we do housing in the US is radically, radically different from the rest of the world.” He began sharing his observations on Twitter (since renamed X) and was joined by Stephen Smith, a New York-based urbanist writer who also frequently posted about architecture and real estate. Eliason, Smith, and a group of like-minded thinkers soon formed an informal coalition (and a group chat), introducing the concept of single-stair housing to American audiences. Ever since, they’ve been making the case that modernizing US building codes to permit this design could unleash more affordable housing nationwide — and their approach is winning even in the face of opponents who warn it’s unsafe. How the US developed its double-staircase standard In the United States, abundant forests and rapid westward expansion made wood the building material of choice. Unlike Europe, where dense cities and a long history of urban fires pushed builders toward brick and stone, Americans prioritized speed and cost — decisions that shaped building safety norms for generations. “The US just had a lot of land, and so our fire protection measures ended up relying more on space,” explains Alex Horowitz, the project director of the Pew Charitable Trust’s housing policy initiative. This strategy of spacing out homes meant that compact building just wasn’t as necessary in America as it was elsewhere. Even today, multifamily housing makes up less than a third of America’s housing stock. For decades, New York City apartment buildings had a single interior staircase. Then came a devastating Manhattan tenement fire in 1860. In response, the New York legislature passed a law requiring fire escapes on new residential buildings. This second exit safety philosophy became deeply rooted in American construction culture. As National Fire Protection Association engineer Val Ziavras put it, “In the United States in particular, free egress is just one of the fundamental concepts that we use as fire protection engineers. … So there’s that underlying concern that when there’s only one exit stair, we’re taking away people’s choice.” Tragedies like the Triangle Shirtwaist Factory fire only deepened this mindset. When a fire broke out on the upper floors of a 10-story factory in 1911, firefighters arrived quickly, but their ladders couldn’t reach the blaze. Dozens of workers — many of them young immigrant women — were trapped behind locked exit doors, a common anti-theft practice at the time. With no way out, some jumped from windows to escape the flames. In just 30 minutes, the fire killed 146 people. Today, nearly all American cities require apartment buildings at least four stories tall to have two staircases, following standards set by the International Code Council (ICC), a nonprofit that develops building codes. This remains the case even as other modern safety features have made multifamily housing remarkably safe. Easing the housing crunch It typically costs less to rent in smaller buildings, yet such “missing middle” housing options — buildings with just two to 19 units — have become increasingly rare in the US, accounting for just a fifth of all housing units built since 2001. Zoning restrictions, building code requirements, and pressure to maximize profits on expensive land help explain why. For advocates like Eliason and Smith, allowing single-stair construction for buildings up to six stories offers a practical solution. According to research from Pew and the Center for Building North America (which Smith leads), adding a second stairway to a six-story apartment complex can require more than $300,000 in construction costs, while four-story buildings could face an estimated $258,000 increase. Eliminating this second staircase could cut costs by about 10 percent and encourage developers to build more desperately needed “missing middle” housing. Beyond direct construction costs, the second stairway and its connecting corridor can also eat up a lot of space — taking up as much as 7 percent of a building’s floor area in small- and medium-sized buildings. These constraints have real-world implications. Despite the influx of millennials to urban centers over the past 15 years, cities have struggled to retain families with children, sometimes due to limited housing options. Even in places with loosened zoning laws, most new construction favors studios, one- and two-bedroom apartments. Single-stair buildings allow for more varied unit layouts, since the apartments can be arranged more freely around a central staircase. That flexibility could make it easier to build more family-friendly three- and four-bedroom units — now a rarity in 21st-century American construction. The impact could be especially dramatic in dense cities, where many small lots remain undeveloped. Sean Jursnick, an architect in Colorado, found approximately 14,000 small lots in Denver where single-stair construction could make development more viable. Similar research identified 90,000 potential parcels in Portland, Oregon, and projected that 130,000 new homes could be added near transit in Boston. Affordable at what cost? Many housing policy ideas face resistance from existing homeowners, but single-stair advocates have found that their biggest opposition comes from fire safety officials. These leaders question the validity of international comparisons, and stress that decreased apartment fires in the US are largely due to safety protocols like second stairwells. The International Association for Firefighters, representing unionized firefighters across the US and Canada, took a firm stance in their position statement this year: > While we understand and support the urgent need for additional affordable housing, [we] also believe that all housing must be safe housing. The removal of two exits—a critical safety design feature—is not an acceptable trade-off for additional housing. Fire safety leaders are particularly frustrated by the new legislative approach to revising building codes, which involves giving less weight to third-party organizations like the International Code Council (ICC) and the National Fire Protection Association (NFPA). For decades, these groups have convened experts and industry leaders to develop safety recommendations that would then be codified into law. “Most legislators don’t have the technical experience to evaluate these arguments,” Sean DeCrane, the IAFF’s assistant to the General President for Health and Safety, told me. “The [ICC] code process brings together technical experts to evaluate reports and consider trade-offs. How do you get the proper experts to all 50 states to have that discussion?” But armed with research, persistent posting on social media, and mounting pressure from the housing crisis, single-stair advocates have continued to sway those in power. They argue that features like sprinklers make the design just as safe — and note that countries allowing single-stair buildings don’t report more fire deaths. Since fires are more common in single-family homes than in new apartments, they say current rules may actually steer people toward less safe housing. And for years, they add, US building codes have been dominated by single-family homebuilders, with little input from those focused on affordable apartments for families. “We live in a democracy, and ultimately, politicians are the representatives of the people, not committee members at NFPA and the ICC,” Smith told Vox. “These experts make important contributions, but their organizations have their own politics. They are not neutral. They are not completely clear-minded engineers looking at facts without commercial interests.” Eliason agrees, and suggests that opposition stems largely from comfort with the status quo. “Resistance to change is endemic to not just the fire industry but construction as a whole,” he said. “I think in the fire departments’ view, single-stair is such a radical departure from the way they’ve historically done things that they just don’t really understand the tradeoffs and benefits. There’s also this aspect of thinking that what we do in the US is superior to everywhere else.” The power of demonstrating it’s possible Despite the nationwide shift to double-stair requirements, several places have carved out exceptions. New York City first established its single-stairway allowance for mid-rise buildings in 1938, aiming to balance fire safety with the growing need for affordable housing on narrow lots, where adding a second staircase often wasn’t feasible. Seattle took its own approach in the 1970s, allowing single-stairway apartment buildings if they had safety features like an exterior stairway or a “smoke-proof tower.” Seattle’s code also later capped each single-stair building at six stories. A handful of other jurisdictions have found their own middle ground: Honolulu adopted Seattle’s model in 2012, while Georgia, Vermont, and Puerto Rico all permit single-stairway buildings up to four stories tall. Research led by Pew and the Center for Building in North America compared fire department statistics from Seattle and New York against the 100 US cities with the highest number of residential fires — and found no evidence of unique challenges or worse outcomes. This evidence, combined with the global prevalence of single-stair buildings, has fundamentally challenged the conversation around building codes in America. Fire officials in other cities sometimes argue in favor of stricter building codes because they lack the fire safety resources of Seattle. But Smith pushes back, noting that many of these places don’t even allow four-story multifamily buildings — so the concern is moot, since those kinds of developments aren’t being built anyway. “Seattle is a very normal big city in America,” Smith added. “Seattle does not have a fire department head and shoulders above that of Jersey City, New Jersey, or Washington, DC.” In fact, when policy experts approached Seattle fire officials about their markedly divergent building code, they were met with a surprising response: “‘I’m so sorry to tell you but to us this is just the code, this is how we do it,’” as Alex Armlovich, a housing analyst at the Niskanen Center think tank, recounts. “It was this emperor’s no clothes moment.” Seattle had been safely allowing single-stair buildings for decades without even considering it worth studying. Smith sees a deeper logical flaw in how fire officials approach the issue: “The kind of logic that they’ll often use is, ‘We’re allowing things [in the code] that I already don’t like, so we can’t allow anything else that I don’t like.’ Whereas I look at it and say, ‘We should treat all buildings the same.’” Do we need more research? Fire safety experts and housing advocates are sharply divided over whether current evidence on safety is enough to justify revising the building codes. Fire officials consistently argue that more research is essential. In September 2024, the National Fire Protection Association hosted an international symposium to explore the issue. (Smith was in attendance and gave a presentation.) Following the event, the group concluded there was a need for more detailed comparisons, for more granular and consistent data, and for more research into how people’s behavior, abilities, or circumstances affect fire risk. The NFPA announced plans to sponsor a research project through the Fire Protection Research Foundation to gather more information. DeCrane of the IAFF was unimpressed with the symposium, calling it “very disappointing” and alleging it was “geared towards the proponents” of single-stair buildings. “It seemed that they wanted to come out with a process that appeased everybody,” he told me. “And we’re dealing with a life safety concern here, so we shouldn’t be appeasing everybody.” [Image: National Fire Protection Association’s single-star symposium in September 2024. https://platform.vox.com/wp-content/uploads/sites/2/2025/04/3E62B55F-85E9-4AE8-ADBA-4121EBEBF99A.jpeg?quality=90&strip=all] The International Association of Fire Fighters has gone further, arguing that proponents haven’t shown how taller single-stair buildings deal with evacuation, fire operations, or resident safety. The union outlined six specific research areas they believe need further study: * Simulations of evacuation times * Congestion in stairwells * Demographics of occupants * Stairway designs * Impact of smoke entering a stairwell * Movement patterns Meanwhile, housing advocates and researchers argue that sufficient evidence already exists to move forward. Armlovich puts it bluntly: “We don’t have to take the NFPA people seriously on this because we have the entire world and NYC and Seattle.” He acknowledges there are still open questions around construction types that warrant further study. But he believes the existing evidence “is enough that I sleep soundly.” Smith similarly recognizes there are some unresolved questions but considers them far less urgent than the IAFF suggests. “I definitely do have questions about how we would safely build a high-rise single-stair building. … I have some questions about the smoke control systems that are used in Europe, whether they really work that well or not,” he said. “But [American] standards for apartment buildings are already so intense...the alarm systems, the sprinklers — we have so much that they don’t have in Europe already.” Smith notes a structural problem: In the US, building code research is often driven by private interests, unlike other countries where governments take the lead. “There’s no single-stair industry” to fund studies in America, he points out, unlike mass timber, which had timber industry backing. Codes are a’changing The rapid momentum of the single-stair movement has surprised even its most ardent advocates. To date, at least 15 states — including California, Minnesota, Montana, Tennessee, and Virginia — have passed laws or amended regulations to allow single-stair design in four- to six-story buildings, or are actively considering such changes. Most of these reforms have materialized just within the last two years. (Though some reformers have their eyes set long-term on greater heights — and indeed, legislation proposed in North Carolina this year would allow single-stair buildings up to eight stories — for now, the six-story push represents the path of least resistance.) “It has been frankly a little faster than I expected,” Smith told me. “I think it’s because it’s a new topic that people did not realize was an issue. Building codes and standards can be so boring and dry. But what’s so interesting about single stairs is that it’s not just that it can be up to 10 percent of the cost of the building. The design implications are very exciting to people.” The most “aggressive” state in adopting single-stair reform so far has been Tennessee, which passed legislation in 2024 to allow local jurisdictions to change their building codes. So far, at least three — Knoxville, Jackson, and Memphis — have done so. "“I guess success would be there’s no housing shortage, and we’ve developed super walkable neighborhoods with abundant housing and multigenerational housing.”" - Michael Eliason Minnesota took a different approach, investing over $200,000 into studying single-stair. A report on the findings is due by the end of the year. Even in places that haven’t yet passed legislation, the conversation is advancing quickly. Steve Waldrip, senior housing adviser for Utah’s Republican Gov. Spencer Cox, told me that his team plans to make single-stair reform a priority in 2026 despite encountering initial resistance this year. “No one wants to be first, no one wants to be on the ledge, particularly when it comes to life safety issues,” he said. “But there’s a rising tide across the country that provides some security and safety in numbers.” In Virginia, Democratic Delegate Adele McClure became a champion for single-stair reform after constituents from Northern Virginia approached her about the concept. She sponsored legislation last year to establish a study group of stakeholders to evaluate the idea, which passed unanimously. While she initially encountered resistance from fire code officials, McClure found that including them in the process helped bring opponents on board. The experience also counters the notion that legislative approaches preclude technical expertise. For McClure, one of the biggest victories was simply getting people to consider an option that “hadn’t been considered at all prior.” Even the ICC has shown some flexibility. The organization is likely to increase its single-stair height limit from three to four stories in its 2027 edition — a modest change, but significant given the conservatism of code development. Housing advocates aren’t content to wait around. As Smith puts it, building codes are “a whole body of laws that have just traditionally flown totally under the radar, and as a result, [the field] developed some bad habits. I think those are sort of coming to light now.” Twenty years from now, Eliason hopes their advocacy will have helped transform American cities. “I guess success would be there’s no housing shortage, and we’ve developed super walkable neighborhoods with abundant housing and multigenerational housing,” he said. “We need this broad array of housing types — social housing and market-rate housing and condos and co-ops. Single-stair, at least, helps to unlock some more opportunities.” Correction, May 8, 9:45 am ET: A previous version of this story misstated who helped fund studies to support mass timber.

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The deceptively simple reform that could unlock more housing