The architecture of modern apartment living in North America is often defined by a silent, invisible constraint: the requirement for two exit stairways. This single regulation, embedded deep within building codes for over a century, has dictated the shape of our cities, the layout of our homes, and the rising cost of our rents. However, a movement to legalize "single stair" apartment buildings—professionally known as Point Access Blocks—is gaining momentum across the United States and Canada. By shifting the paradigm of how people move vertically through a building, urban planners and architects believe they can unlock a future of more affordable, family-friendly, and naturally lit urban housing.

Understanding the Point Access Block Typology

A single stair apartment building, or Point Access Block, is a multi-family residential structure served by one central staircase for both daily access and emergency egress. In this configuration, apartments are arranged directly around a central landing or a very short hallway.

Unlike the sprawling apartment complexes typical of American suburbs, Point Access Blocks are compact. They represent a dominant building form in Europe, parts of Asia, and Latin America. In cities like Berlin, Paris, or Tokyo, it is common to find six-story buildings where three or four apartments share a single stairwell and an elevator. This efficiency allows for a significantly smaller building footprint, making it the ideal typology for "infill" development—building on small, narrow, or irregularly shaped urban lots that are otherwise unbuildable under current North American mandates.

The Contrast with Double-Loaded Corridors

To appreciate the single stair building, one must understand its alternative: the double-loaded corridor. Most modern American apartment buildings are designed like hotels. A long, windowless central hallway runs the length of the building, with small units—typically studios and one-bedroom apartments—lined up on either side.

This design is a direct consequence of the "two-stair" rule. To justify the cost and space consumed by two separate stairwells (usually placed at opposite ends of a building), developers must maximize the number of units served by those stairs. The result is a massive, bulky building that requires large plots of land and produces deep, narrow apartments that only have windows on one side.

The Tragedy of the Double-Loaded Corridor

The prevalence of double-loaded corridors has led to a stagnant era of residential design. When a building is forced into this layout, the quality of life for the inhabitants is compromised in several measurable ways.

The Loss of Natural Light and Ventilation

In a double-loaded corridor, apartments are essentially "single-aspect." They have windows only on the exterior wall. This means that natural light cannot reach the back of the unit, and cross-ventilation is physically impossible. In an era where energy efficiency and indoor air quality are paramount, the inability to open windows on two sides of a home to create a breeze is a significant architectural failure.

Point Access Blocks, by contrast, allow for "through-units." Because the apartments wrap around the corners of a small central core, they can have windows on two or even three sides. This design provides superior natural lighting and allows residents to cool their homes naturally, reducing reliance on energy-intensive air conditioning.

The "Bowling Alley" Apartment Problem

Because developers need to pack as many units as possible along a long hallway to offset construction costs, apartments often become long and narrow—jokingly referred to as "bowling alley" units. These layouts are difficult to furnish and feel claustrophobic. Perhaps more importantly, they are rarely suitable for families. It is nearly impossible to fit three bedrooms into a narrow, single-aspect unit while providing windows for each room. This is why the modern American apartment market is dominated by small units for singles and couples, pushing families to the suburbs in search of light and space.

A Historical Legacy of Fire and Fear

The requirement for two stairways in North America is not an arbitrary design choice; it is a reaction to historic tragedy. In the late 19th and early 20th centuries, massive urban fires devastated cities like New York, Chicago, and San Francisco. The 1911 Triangle Shirtwaist Factory fire in NYC, which killed 146 garment workers because of locked exits and inadequate stairways, remains a cornerstone of fire safety education.

In response, North American building codes adopted a "redundancy first" approach. The logic was simple: if one stairwell is blocked by smoke or fire, residents must have a second way out. This led to the universal mandate that any residential building taller than three stories must have two independent exits.

While this logic was sound in 1911—when buildings were made of wood, lacked internal sprinklers, and had no automated smoke detection—architects argue that the world has changed. In Europe, the response to fire was different. Rather than requiring more exits, European codes focused on "compartmentalization" and non-combustible materials. By ensuring that a fire cannot spread from the unit where it started, the need for a second stairwell is mitigated.

Economic Impact: Unlocking the Missing Middle

One of the most compelling arguments for single stair reform is economic. The current two-stair mandate creates a high "barrier to entry" for housing development.

Reducing Construction Costs

Research from organizations like the Pew Charitable Trusts and the Center for Building in North America suggests that single stair buildings can be 6% to 13% cheaper to construct than their dual-stair counterparts. This saving comes from several factors:

  1. Reduced Square Footage: Eliminating a second stairwell and the long connecting corridors saves significant floor area. In a small building, a second stair can consume 10% or more of the total buildable space.
  2. Increased Efficiency: More of the building's total area is "rentable" or "saleable" rather than being lost to "circulation" (hallways and stairs).
  3. Simpler Structural Design: Small, compact cores are easier to engineer than sprawling, multi-stair complexes.

Unlocking Small Urban Lots

In many dense cities, the most available land for new housing is found on small "infill" lots. Under current two-stair codes, these lots are often impossible to develop profitably. If you have a lot that is only 50 feet wide, by the time you put in two stairwells and the required hallway, there is almost no room left for actual apartments.

Legalizing single stair buildings up to six stories allows these small lots to become viable sites for housing. This creates "Missing Middle" housing—buildings that are larger than a single-family home but smaller than a massive high-rise—which is essential for maintaining urban density and neighborhood character.

Addressing the Fire Safety Debate

The primary opposition to single stair reform comes from fire service associations. Their concerns are understandable: a single exit route means there is no "Plan B" if that stairwell becomes compromised. However, modern fire safety science provides a robust set of tools to make single stair buildings as safe as, or even safer than, traditional dual-stair buildings.

Modern Mitigation Strategies

For a single stair building to be safe at heights of 4 to 6 stories, certain "trade-offs" are required in the building code:

  • Automatic Sprinkler Systems: Comprehensive NFPA 13 sprinkler systems are a non-negotiable requirement. These systems are highly effective at suppressing fires before they can spread to common areas.
  • Pressurized Stairwells: Modern systems can pump air into the stairwell during an emergency to keep smoke from entering the exit path.
  • Non-Combustible Construction: Many reform proposals require single stair buildings to be built from Type I or II (steel/concrete) or Type IV (mass timber) materials, rather than traditional light-frame wood.
  • Travel Distance Limits: Residents must be within a very short distance of the stairwell door (often less than 20 feet) to ensure rapid egress.
  • Rescue Openings: Every unit must have windows that are accessible to fire department ladder trucks, providing a second "egress" through the exterior.

Evidence-Based Safety Records

The data supports the safety of these buildings. A study by the Pew Charitable Trusts analyzed fire death rates in modern single stair buildings in New York City and Seattle—two of the few U.S. cities that have long allowed this typology. The study found that from 2012 to 2024, the rate of fire deaths in these buildings was no different than in dual-stair buildings. In fact, not a single death was recorded during that period where the lack of a second stair was a contributing factor. International data from the Netherlands and Switzerland, where single stair buildings are the norm, shows similar levels of high safety.

Design Potential for Families

Beyond economics and safety, there is a social dimension to the single stair debate. One of the biggest challenges in urban housing today is the lack of units large enough for families. When developers are forced to use double-loaded corridors, it is almost impossible to design a three-bedroom apartment that feels like a home rather than a dormitory.

In a Point Access Block, the layout is flexible. Because units can occupy entire corners or even entire floors, architects can easily design three- or four-bedroom apartments with multiple windows, separate dining areas, and "quiet zones" away from the living area. By making it easier to build family-sized units in the city, single stair reform can help prevent the "family flight" to the suburbs, keeping communities diverse and vibrant.

The Future of Building Codes: A Policy Shift

The tide is beginning to turn. For decades, the International Building Code (IBC) has strictly limited single stair residential buildings to three stories. However, several jurisdictions are now leading the way in reform:

  1. Seattle, WA: Seattle is the pioneer, allowing single stair buildings up to 6 stories (or 75 feet) for decades. This has resulted in a unique architectural landscape of mid-sized, high-quality apartments.
  2. New York City: NYC allows single stair buildings up to 6 stories under specific conditions, which has helped maintain the density of boroughs like Brooklyn and Queens.
  3. Honolulu, HI: Similar to Seattle, Honolulu has long utilized this typology to manage its limited land area.
  4. Denver, CO: In 2025, Denver proposed new code provisions to allow 5-story single stair buildings, aligning with state-level legislation (HB 1273) aimed at solving the housing crisis.
  5. British Columbia, Canada: The province has recently moved to allow single stair buildings up to six stories, citing the need for more efficient and affordable housing.

The 2027 edition of the International Building Code is currently under review, with proponents pushing for a national standard that would allow single stair buildings up to four or five stories across the United States.

Summary

The single stair apartment building is more than just a technicality in a building code; it is a fundamental tool for better urban design. By moving away from the sprawling, inefficient, and often alienating double-loaded corridor model, cities can encourage the construction of smaller, more affordable, and more livable housing. While safety must remain the priority, modern technology proves that we can protect lives without sacrificing the quality of our homes. As more states and cities adopt these reforms, we may finally see the return of the "Missing Middle"—housing that serves families, respects neighborhood scale, and creates a more sustainable urban future.

FAQ

What is the maximum height for a single stair apartment building?

Historically, most U.S. codes limited them to 3 stories. However, recent reforms in places like Seattle and British Columbia allow them up to 6 stories, provided they meet strict fire safety requirements like sprinklers and pressurized stairs.

Why are single stair buildings cheaper to build?

They eliminate the need for a second stairwell and long, windowless corridors. This reduces the overall square footage of the building while increasing the amount of "rentable" space, making the project more economically efficient.

Are single stair buildings a fire trap?

No. Modern single stair buildings are equipped with advanced fire suppression systems, including full sprinklers, fire-rated walls, and smoke control systems. Data from cities like Seattle and NYC shows they have a safety record comparable to traditional buildings.

How do single stair buildings help families?

Because the floor plans aren't constrained by a long central hallway, architects can design "through-units" with windows on multiple sides. This makes it much easier to create spacious three-bedroom apartments that are attractive to families.

What is a Point Access Block?

"Point Access Block" is the architectural term for a building where apartments are clustered around a single vertical circulation core (stairs and elevator). It is the most common term used in international architecture for single stair buildings.