Key Takeaways:
- Modern stairway requirements have been created after a long history of development of U.S. building codes, many in response to fatal fires.
- The materials used for U.S. houses, as well as the potential escape routes and other safety measures were analyzed in the creation of new standards and policies.
- As more safety measures are implemented, debates about which stair measures are necessary have expanded.
What is the Current Regulatory Landscape?
Today, most U.S. jurisdictions require two interior staircases for residential buildings above three stories. The International Building Code (IBC) serves as the predominant model code of the U.S., though adoption and modification occur at the state and local level.
The IBC generally limits single-stair residential buildings to three stories. However, at least six major U.S. jurisdictions have modified this standard to allow taller single-stair buildings under defined conditions: these are New York City, Seattle, Honolulu, Puerto Rico, Georgia, and Vermont.
Within the U.S., variation still exists. Vermont follows the National Fire Protection Association (NFPA) code, rather than the IBC, and permits certain four-story single-stair buildings with unit limits. Chicago allows single-stair townhouses up to four stories. Dallas permits “scissor stairs” in buildings up to approximately five or six stories, which provide two interlocking stairways within a single shaft. These differences illustrate that the two-stair requirement is not universal, but instead shaped by local and regulatory traditions.
In recent years, interest in stairway reform has grown alongside broader housing supply concerns. Rising housing costs, constrained land availability, and declining construction of small-and medium-sized housing have led some policymakers to examine whether building code requirements affect development feasibility. In this context, stairway reform is often discussed as part of a broader effort to expand housing supply including mid-rise and “middle housing” forms that can fit on small or infill parcels of land.
Where Did Stairway Requirements Come From?
Modern stairway and exit requirements in U.S. building codes developed in response to fatal urban fires in the 19th and early 20th centuries. A February 1860 New York Times report described a tenement fire in Lower Manhattan in which approximately 30 residents were believed to have died after flames spread through a single, unprotected wooden staircase. Similar incidents reinforced the risks associated with limited means of evacuation in multi-story housing.
Throughout the late 1800s and early 1900s, cities adopted fire escapes, enclosed stairwells, and eventually requirements for multiple interior exits. By the mid-20th century, two interior staircases had become standard practice in many jurisdictions. The 1938 New York City building code permitted limited single-stair configurations under certain conditions, but later included revisions, including the 1968 code, reinforced interior stair redundancy, and eliminated exterior fire escapes. Seattle experienced a fatal residential fire in 1971 that influenced West Coast safety standards in a similar way.
These policies reflected the construction practices of their time. Much of U.S. housing relied on light wood-frame construction, and sprinkler systems were not yet widespread. Over time, requiring two interior staircases for residential buildings above three stories became a widely-adopted precautionary standard in American codes.
Safety Outcomes and Development Impacts
Supporters of reform argue that modern fire protection systems significantly reduce the risks that originally justified universal two-stair requirements. Modern apartment buildings are typically equipped with automatic sprinkler systems, fire-rated walls, enclosed stairwells, and self-closing doors.
A 2025 Pew study analyzed 347 fatal residential fires in New York City between November 12, 2012, and March 21, 2024. Researchers identified 4,440 modern four-to-six-story single-stair buildings constructed under NYC’s post-1968 provisions. During the study period:
- Two fatal fires occurred
- Three total civilian deaths occurred
- One fire death occurred per 205,934 occupant-years.
By comparison: all other NYC residential buildings experienced:
- 345 fatal fires occurred
- 465 total deaths occurred
- One fire death occurred per 220,907 occupant-years
The difference — approximately five deaths per million occupant-years in both categories — was not statistically significant. Researchers also found that none of these deaths in modern single-stair buildings involved smoke or fire penetrating the stairway.
Cost is another major consideration. By requiring fewer staircases, the cost of construction can be lowered by hundreds of thousands of dollars per apartment building. Estimates for constructing an additional interior stairway in a six-story multifamily building range from $190,000 to $380,000, with one four-story estimate at $228,000. For a hypothetical six-story building with 2,000 square feet per floor at $250 per square foot (approximately $3 million total cost construction), a second staircase can represent between 6 percent and 13 percent of total hard costs.
Proponents also note broader housing implications. Small- and medium-sized apartment buildings make up roughly 40 percent of the U.S. rental stock, yet only 22 percent of apartment units built since 2000 have been in this size category. One study found that 76 percent of land parcels in Boston and its inner suburbs could physically accommodate four-to-six story single-stair buildings, and developing just 3 percent of those parcels near transit could yield up to 130,000 units.
Single-stair configurations can also enable more compact floor designs that fit on narrow or irregular urban lots. In Seattle, for example, clustered units around a central stair have been used to create infill housing on small parcels. Proponents argue that this design flexibility can expand development options while improving light and ventilation within units.
Redundancy, Risk, and Implementation
Opponents emphasize redundancy as a foundational fire safety principle. Fire service organizations such as the International Association of Fire Fighters argue that multiple means of egress remain a fundamental safeguard, particularly in scenarios where a stairwell becomes compromised by smoke. From this perspective, layered protections such as sprinklers, alarms, fire-rated materials and multiple exits, work together to reduce risk.
There are also concerns about the reliability and maintenance of advanced fire protection systems. Karen Grove, Seattle’s Executive Director of Fire Prevention, says pressurized stairwells and other smoke control systems require ongoing inspections and upkeep. If these systems are not properly maintained, safety margins may diminish over time.
Another concern relates to emergency response capacity, which varies by jurisdiction. In Seattle, researchers identified 36 fatal fires (42 deaths) during this study period, with only one potentially occurring in a modern four-to-six story single-stair building. While this suggests rarity, fire officials caution that smaller or volunteer fire departments may have slower response times or fewer resources, including ladder trucks capable of reaching upper floors. In such contexts, a single compromised stair could pose greater risk.
Process concerns are also central. Some fire officials also argue that legislative reforms enacted at the state level bypass the traditional national code consensus process, which involves technical review by engineers, fire professionals and other stakeholders.
Recent Developments
Since 2022, 19 states and Washington, D.C. have introduced legislation to study or allow single-stair buildings, typically with limits on height and building size. In 2025, several states, including Colorado, Montana, New Hampshire, and Texas, adopted bipartisan measures allowing certain single-stair residential buildings. Maine is in the process of implementing similar changes, while Maryland has convened study groups to examine the issue.
Locally, cities such as Austin have recently permitted single-stair construction up to five stories in 2025. Other jurisdictions are considering reforms with height limits and caps on the number of units per floor. These measures often include additional fire safety requirements tailored to single-stair designs. The pace of reform varies, but the issue has moved from a niche architectural debate to a topic of state-level legislative consideration in multiple regions.
Conclusion & What’s Next
Single-stair reform presents a measurable policy trade-off. Two-stair requirements emerged from an era of limited fire suppression technology and high urban fire risk. Today, modern buildings incorporate sprinklers, fire-rated materials, smoke detection, and compartmentalization.
At the same time, life safety redundancy remains a central principle in fire protection philosophy and concerns about maintenance, enforcement, and emergency response capacity continue to shape opposition. As more states consider legislative changes, policymakers face a balancing act between housing development goals and long-standing safety norms. Whether and how stairway requirements evolve will likely depend on how decision-makers weigh empirical safety evidence, institutional processes, and local capacity.
FAQ
Q: Why do different U.S. states have different reforms or regulations for single-stair laws?
A: There is a complex process for developing and passing reforms and regulations, and the changes of this passing in committee, and the advocacy from external organizations, varies by state. Read more about this here.
Q: Why is cost relevant?
A: The cost of adding or removing stairways is related to the potential for constructing more buildings. As housing costs rise in the U.S., economic concerns are at the forefront of many of these discussions.
Q: Do all major cities allow the same rules as New York City, Seattle, Honolulu, Puerto Rico, Georgia, and Vermont?
A: No, only New York City, Seattle, and Honolulu, have made these changes, while other major cities “stipulate that apartment buildings four to six stories must have two stairways.”