Single-stair Multifamily Codes Trend As States Lean Into Affordability

Single-stair small multifamily housing has shifted from a niche building type to a momentum-driven national reform trend in recent months, as cities and states seek to expand housing affordability through “missing middle” construction.​

As of now, 19 states have introduced or passed bills or commissioned studies on single-stair construction, meaning the trend has a long way to go before it reaches critical mass. Last year, Colorado, Texas, Montana, and New Hampshire enacted new legislation, while Los Angeles and Nashville are among the cities that made the switch.​

Minnesota is now considering allowing single-stair construction up to six stories, based on a study showing that single-stair designs can be safe in taller buildings when other fire safety conditions are in place. The Minnesota study could serve as a model for how other states and cities build evidence to support allowing single stairways in new, taller residential buildings.​

“This report proves what is possible when we reexamine longstanding housing regulations,” Nick Erickson, executive director of the Housing Affordability Institute, writes on LinkedIn.​

States and cities are targeting changes to stairway requirements in building codes to enable small increases in density alongside zoning changes. The shift reflects a broader inflection toward scrutinizing building codes as a tool for density increases, even modest ones.​

Dallas, for example, adopted an ordinance last year that applies the residential International Building Code to multifamily construction in developments up to eight stories. In many developers’ view, the commercial IBC had made smaller projects too costly to build, effectively shutting out small developers.​

The new Dallas code applies only in multifamily zoning districts. It reflects city planners’ sensitivity to Dallas’ long history of favoring single-family districts, even as other cities have ended single-family zoning outright.​

“Anytime you think about adding even an accessory dwelling unit in the single-family areas, it is going to be a big fight,” Emily Liu, Dallas planning director, tells The Builder’s Daily. “So right now we’re looking at the building code.”​

Single stair in the making

For context, two-stairway requirements for apartment buildings emerged piecemeal over the 20th century, tied to major fires and early model codes. In their modern form, they are embedded in the IBC and similar model codes, which typically require two exits once buildings rise above approximately three stories or exceed certain floor‑area and occupant‑load thresholds.​

Over the past two years, Minnesota planners and building inspection officials have studied whether to expand beyond the current three-story limit. The legislature funded the research, which was delivered at the end of December 2023. In November 2024, a technical advisory group of the state’s Construction Codes Advisory Council unanimously approved a single-stair proposal for buildings up to six stories.​

Minnesota’s review of single‑exit stairway apartments boiled down to a simple question: when is it acceptable to skip the second staircase and keep people safe, while allowing builders to add more useful, lower‑cost housing?​

The effort is less a code exercise than an attempt to draw a clear line between a smart trade-off and a gamble. The goal is to enable more small urban apartment buildings without increasing risk.​

Key safety findings

The safety analysis makes a clear point: the extra stair matters most in worst‑case fires. Those scenarios involve sprinkler failure and a resident leaving an apartment door open, allowing smoke to pour into the hallway and stairs.​

In most typical fires, sprinklers work, and residents keep doors closed. A single, well‑protected staircase, short hallways, and modest floor sizes still give people enough time to escape safely in mid‑rise buildings.​

Recommended single stair building codes guardrails

The report does not argue for “single stair everywhere.” Instead, it lays out guardrails for when a one‑stair building makes sense.​

The criteria include a height cap of roughly six stories or 75 feet, floor plates in a modest size range, limits on how many apartments fit on each floor, and strict rules for how far anyone can be from the stair. The idea is to keep escape routes short and avoid long, smoky hallways in a fire.​

Fire‑safety features are non‑negotiable.

Full sprinklers, rated corridors and stair enclosures, tight limits on dead‑end corridors, and strong smoke detection and alarms all count as must‑haves, not options or upgrades. For taller buildings within the allowed range, the report also treats elevators as essential to ensure that disabled residents have a fair chance of safe evacuation throughout the building’s life and that firefighters can perform their duties.​

Policy implications for single stair building codes

On the housing side, the payoff is floor space. Removing the second stair increases the residential space on each level, making it easier to design family‑sized, cross‑ventilated units on tight infill lots that currently do not pencil out. The report directly links this to Minnesota’s need for smaller, neighborhood‑scale apartment buildings, which often fail to start due to the two‑stair rule.​

Still, the document stops short of writing policy on its own. It frames the findings as technical backing for lawmakers and code councils.​

The report also argues that any move to allow rigorous inspections and ongoing data tracking should accompany single‑stair buildings so that the state can tighten or relax the guardrails based on real‑world experience.​

“Using data-driven decisions, building codes can be a powerful tool to increase both housing affordability and supply,” Erickson, who served on the advisory group overseeing the study, said.​