As the United States grapples with a persistent and multifaceted housing shortage, policymakers are increasingly looking beyond traditional zoning reforms. While conversations about density and exclusionary zoning have dominated the urban planning discourse for years, a more technical—yet arguably more impactful—battle is being fought in the pages of local building codes. Specifically, the movement to reform "single-staircase" requirements is gaining unprecedented momentum, promising to unlock the potential for "missing middle" housing that has been stifled by rigid, decades-old regulations.
The Core Conflict: Why Two Staircases Became the Standard
For the better part of a century, American building codes have largely mandated that multi-family residential buildings above a certain height be equipped with at least two separate egress staircases. This requirement, intended to provide redundant escape routes in the event of a fire, effectively mandated a specific, "double-loaded corridor" building typology. In this configuration, apartments must be positioned on either side of a long, central hallway to reach two distant fire stairs at opposite ends of the structure.
While this design provides a clear path for egress, it carries significant economic and spatial baggage. Double-loaded corridors require substantial floor area dedicated to hallways, which are non-revenue-generating spaces. Furthermore, because units must be deep to reach the central corridor, these buildings are often forced into larger footprints that are difficult to fit onto narrow urban lots. This effectively kills the viability of small-scale, "human-scale" apartment buildings—the very structures that historically defined vibrant, walkable neighborhoods before these codes were standardized.
Chronology of the Reform Movement
The push to modernize these codes has not been a sudden trend, but rather a slow-building coalition of architects, urbanists, and housing advocates.
- Early 20th Century: The standardization of the "two-stair" rule becomes entrenched in American building codes, largely following catastrophic fires in early high-rise developments.
- The 2010s: Urbanists begin to point to international precedents. In cities like Berlin, Paris, Tokyo, and even Seattle (for specific building types), single-staircase buildings have functioned safely for decades, allowing for high-quality, light-filled apartments that occupy the full width of a building.
- 2023–2024: Momentum shifts from theoretical discussion to legislative action. Advocacy groups, including The Pew Charitable Trusts, release white papers detailing the safety record of modern, fire-sprinkler-equipped, single-staircase structures.
- 2025: The movement hits a tipping point. According to data from The Pew Charitable Trusts, seven states enact legislation to permit or study the expansion of single-staircase residential buildings, marking a major departure from the status quo.
Supporting Data: Efficiency vs. Safety
The economic argument for single-staircase reform is rooted in floor-area efficiency. By eliminating the need for a second stairwell and the long, redundant hallways required to reach it, developers can increase the "net-to-gross" ratio of a building. This means more square footage can be dedicated to actual living spaces rather than circulation, potentially lowering the per-unit cost of construction.
However, the safety data remains the primary hurdle for proponents. Advocates often cite the evolution of fire suppression technology. Unlike the buildings of the 1920s, modern structures are required to have automatic fire sprinklers, advanced fire-rated wall assemblies, and interconnected smoke detection systems.
A comprehensive report by The Pew Charitable Trusts highlighted that small, single-stairway apartment buildings have maintained strong safety records in jurisdictions where they are allowed. The study argues that the redundant safety features in modern construction—specifically the presence of sprinklers—mitigate the risk that the two-stair rule was originally designed to address.
Official Responses and the California Precedent
The debate is perhaps most visible in California, where the tension between housing urgency and public safety is acute. In March, the California Office of the State Fire Marshal issued a nuanced report that served as a reality check for aggressive reformists.
While the Fire Marshal acknowledged that building codes could be modernized, they urged a cautious, incremental approach. The report recommended that single-staircases be permitted in buildings up to four stories—one story higher than the current common standard—rather than the six stories frequently proposed by housing advocates.
"The presence of an additional exit is important for maintaining safety in the face of unforeseen failures, fire spread, or structural compromise," the report noted. This sentiment underscores the primary resistance from fire safety organizations: the fear of "cascading failures." If a single stairwell is blocked by smoke or structural debris, the building’s occupants are effectively trapped, a scenario that professional firefighters are understandably hesitant to accept as a normalized risk.
Implications for the "Missing Middle"
The stakes of this debate are high, specifically regarding the "missing middle"—the housing tier that sits between detached single-family homes and massive, high-rise apartment complexes.
1. Architectural Flexibility
Single-staircase reform allows architects to design "point-access" buildings. These buildings are often small enough to fit onto typical 50-foot-wide urban lots. Because the building is served by a single, central stair, units can be arranged to have windows on two or three sides, providing superior natural light and ventilation compared to the "canyon" feel of double-loaded corridor units.
2. Market-Rate Affordability
By reducing the cost of land acquisition and increasing the number of units that can be built on a standard plot, developers can theoretically pass those savings on to tenants. In a market plagued by high interest rates and labor shortages, every percentage point saved on construction overhead is vital.
3. Urban Density without High-Rises
For cities looking to increase density without resorting to controversial high-rise towers that can change the character of a neighborhood, single-staircase buildings offer a "gentle density" solution. They allow for more homes in existing neighborhoods while maintaining a scale that is compatible with traditional housing stock.
Looking Ahead: The Path to 2026 and Beyond
As more states explore building code reforms, the conversation is likely to evolve into a discussion about "performance-based" versus "prescriptive" codes.
Prescriptive codes, like the current two-stair rule, offer a rigid, easy-to-enforce standard. Performance-based codes, which are more common in Europe, allow for more architectural variety provided the building meets certain safety outcomes, such as time-to-evacuate metrics and fire-resistance ratings.
The challenge for 2026 and beyond will be whether state fire marshals and local planning departments can find a middle ground. This likely means creating a tiered system: perhaps allowing single-staircase buildings up to four stories with advanced safety requirements, and reserving two-stair requirements for taller, higher-occupancy structures.
The ongoing reform of building codes represents a quiet but profound shift in how the United States envisions the future of its cities. By moving away from the rigid mandates of the past, policymakers are opening the door to a more efficient, flexible, and human-centric approach to housing. While safety concerns will—and should—remain paramount, the progress made in 2025 suggests that the "stairwell revolution" is not merely a technical adjustment, but a foundational component of solving the national housing crisis.
