How the New Single-Stair Building Code Changes the Future of American Apartments

On May 29, 2026, the International Code Council (ICC) formally voted to update the International Building Code, raising the height limit for single-staircase apartment buildings from three stories to four. That administrative change, which takes effect in the 2027 model code, alters the geometry of American housing. For decades, the requirement that any building over three stories contain two separate exit stairwells connected by a corridor has dictated what gets built: massive, block-long complexes filled with narrow, single-aspect apartments. By relaxing that rule, the new code opens the door to "point-access blocks"—compact, mid-rise buildings where apartments wrap around a central stair, allowing for windows on multiple sides, cross-ventilation, and family-sized floor plans.[2]

Under the previous code, a second staircase was mandatory, forcing architects to connect the two exits with a long, hotel-style hallway. That hallway consumes 15 to 20 percent of a building's floor area, generating no rent while requiring heating, cooling, and maintenance. To make the math work, developers pack as many small units as possible along both sides of the corridor. The result is the "5-over-1" apartment block: deep, narrow units with windows only on one end, making cross-ventilation impossible and three-bedroom family layouts difficult to design.

For a renter or buyer, the ICC's shift means the next wave of mid-rise construction will look fundamentally different. In a point-access block, two to four units open directly off a central landing. Because the apartments do not stop at a corridor wall, they can span the full width of the building. This dual-aspect design allows air to move naturally through the unit, reducing reliance on mechanical cooling. It also brings daylight into every room, a stark contrast to the windowless interior bedrooms common in modern American apartments.[2]

The second stairway adds significant cost, which can mean the difference between a project being financially feasible or not. According to a 2025 report by The Pew Charitable Trusts, single-stair buildings with four to six units cost roughly 6 to 13 percent less to build than comparable dual-stair designs. They sit on narrower lots and use simpler structural cores. As Ed Smith of the Center for Building in North America noted, "Developing really is a block-by-block knife fight for small amounts of money." Removing the second stair makes infill development viable on standard 25-foot city lots.[1]

The two-staircase rule originated in the 19th century, long before the advent of modern fireproof materials and automatic sprinkler systems. Today, fire unions remain cautious. The International Association of Fire Fighters (IAFF) has argued that single exit designs "jeopardize escape routes and complicate firefighter response." However, the new 2027 code includes strict mitigations: buildings are capped at 4,000 square feet of net floor area per story, and they must feature manual fire alarms, automatic smoke detectors in common spaces, and sprinklers in the stairway.[1]

While the four-story limit is new for the national model code, several jurisdictions have safely built taller single-stair structures for decades. Seattle has permitted six-story single-stair buildings since 1977, resulting in structures like the Pike and Virginia Building. New York City and Honolulu also maintain older exemptions. Internationally, the point-access block is the standard for mid-rise housing; cities like Vienna, Copenhagen, and Barcelona have relied on the typology for a century to build dense, family-friendly neighborhoods.

The ICC's decision accelerates a wave of state-level reforms already underway, providing a tailwind for the "missing middle" housing sector, which saw construction starts backslide in late August 2026 amid zoning headwinds. In 2025, Colorado enacted legislation allowing five-story single-stair buildings, provided they use non-combustible construction and automatic sprinklers. Michigan followed in July 2026 with a four-story allowance, while Massachusetts Governor Maura Healey issued a February 2026 executive order to explore single-stair construction to boost housing production.

The adoption of the 2027 International Building Code does not automatically change local laws; states and municipalities must individually ratify the updated text. But the model code provides the necessary cover for local building departments to act. As zoning reforms continue to target single-family neighborhoods, the single-stair four-story building offers a physical template for "gentle density"—a way to add housing supply that fits seamlessly onto a neighborhood street rather than requiring a massive commercial footprint.[2]