[All images by BUILD LLC]
Many American cities are facing a full-on housing affordability crisis, due in large part to the disappearance of the small apartment buildings that once defined their neighborhoods. These buildings—typically ranging from 10 to 25 units—can fit on lots formerly zoned for single-family homes and fill the overlooked nooks and crannies of the city. Their scale allows for architectural variety and nuance, making them meaningful contributors to the character and cohesion of neighborhoods and communities. They’re perfectly sized to host a corner coffee shop on the ground floor and big enough to add healthy foot traffic to the sidewalk out front. They’re usually small enough to avoid the need for an elevator, yet large enough that egress planning becomes a primary driver of the design. And it’s often precisely the egress code requirements that determine whether these projects pencil out—or never even make it past permitting.
Even a simple stair core in a small multi-family building can easily consume hundreds of thousands of dollars in construction costs. Designing stairways to be pleasant or architecturally expressive only increases the expense. And when building codes require two stairwells by default, the cost essentially doubles—jeopardizing the pro forma, reducing potential profit, and in many cases, killing the project altogether.
Because of this, there’s an important conversation happening right now among architects, developers, builders, and policymakers. Section 1006.3.4 of the International Building Code (IBC) requires two stairwells for any multi-family building over three stories tall. This code typically leads to one of two outcomes:
• If a building is limited to one stair, with a maximum of four units per floor across four stories (including a basement), the result is a 16-unit project. Even at that modest scale, it can be hard to make the numbers work. And if the project isn’t profitable, no smart developer will move forward.
• If you design for two stairs, you can increase the number of units—but you also dramatically increase the cost. To absorb that cost, you need to scale up to 25 units or more. That, in turn, requires a larger footprint, a more expensive lot, more complex permitting, and the list goes on. It quickly becomes a game of diminishing returns until the unit count approaches 80 to 100 units.
To address this conundrum and encourage the development of small multi-family buildings, some cities have adopted local amendments to the IBC allowing additional stories within a single-exit design. Seattle, for instance, permits up to five stories served by a single stair. With four units per floor, that allows for a 20-unit building—often the sweet spot where construction costs and rental income align. Successful examples in Seattle include the King Street Flats (above) and Juniper Flats (below), both of which demonstrate the architectural and economic viability of this typology.
Multiple stairs became a requirement in the late 1800s in cities like New York and Chicago, where fires often cut off escape routes from individual apartments. At the time, this problem was addressed by adding exterior fire escapes—now iconic features of historic brick walk-ups. Then, in the 1970s and 1980s, fire sprinkler systems were added to many building codes, helping suppress fires and allowing residents more time to escape. However, the implementation of sprinkler systems was never accompanied by a re-evaluation of stair requirements for small multi-family buildings. The two-stair mandate stuck around, largely unquestioned, until recently—when escalating construction costs brought the issue to the forefront.
There is now growing support for allowing single-stair buildings, provided they meet other code requirements such as fire sprinklers, egress travel distances, and other life-safety measures. With construction costs in the U.S. reaching all-time highs, this change is not just helpful—it’s necessary if we want this vital housing type to survive.
And because we love a good bullet-point list, here are five key reasons why building codes across the country should allow more stories (and more units) in single-exit stair buildings:
1. Expanding Housing Supply Through Smarter Density
Single-stair buildings support smaller floorplates and more compact footprints, making them ideal for infill sites or irregular urban parcels. This approach enables gentle density increases in neighborhoods where mid-rise projects are often infeasible—or politically unpalatable.
2. Cost-Efficiency and Project Viability
Eliminating the second stair cuts construction costs, increases usable square footage, and enables more efficient unit layouts. For small- to mid-scale multi-family developments, this can mean the difference between a viable project and a stalled one.
3. Improved Design Quality and Livability
Single-stair layouts allow for better unit design – including more natural light, better cross-ventilation, and a more human-scaled building form. The result is healthier, more livable homes.
4. Global Precedent and Proven Safety
Countries across Europe and Asia have long permitted single-stair residential buildings up to five or six stories, and the safety record is strong. When combined with sprinklers, fire-rated construction, and alarm systems, single-exit buildings can meet or exceed performance-based safety benchmarks.
5. Regulatory Barriers and Reform Opportunities
U.S. codes still generally prohibit single-stair buildings above three stories, but reform is gaining momentum. Highlighting successful case studies and updating the code to allow single-exit stairs under clearly defined safety conditions could unlock new, much-needed housing options.
Cheers from Team BUILD
Let us know if you’re interested in building one—chances are we already have a sketch started.