Today, the Massachusetts building code allows multifamily buildings to have a single stairwell with a maximum of three stories or 12 units. A 2024 report by Boston Indicators, Utile, and the Harvard Joint Center for Housing Studies, suggests that in Greater Boston alone, an additional 130,000 new homes could be built if single-stair construction were allowed in four- to six-story buildings.
The downsides of having a second stairwell are cost and layout. Buildings with two stairwells typically have units lining opposite sides of a central corridor, which can limit benefits like natural light and cross-ventilation. According to a Pew study released in February, building a second stairwell and central corridor typically accounts for 6 to 13 percent of total construction costs, and those features take up 7 percent of the building’s floor area.
Minkoo Kang, principal at development consulting firm General Partner Office, has seen the benefits of single-stair construction. After a fire burned down a Cambridge triple-decker in 2021, Kang worked with the condominium association to replace the eight-unit building. Kang proposed converting the building from two stairwells to one, which was allowed because it’s three stories high. As a result, the new units, which are energy efficient and meet modern fire code requirements, are at least 15 percent larger than the old ones. That let units be sold at a higher price, defraying the cost of rebuilding. “The single stair unlocks a big potential for improvement and efficiencies,” Kang said.
Sam Naylor, an architect and associate at Utile, who worked on the single-stair report, said the two-stairwell restriction can be the difference between it being feasible or infeasible to build affordable or market rate housing on small- to medium-size parcels in Boston. The report found that for a typical Boston parcel of 3,000 to 5,000 square feet, requiring a second stairwell adds between $200,000 and $500,000 to construction costs.
This isn’t solely a Massachusetts issue. Most US states have a three-story limit, although Vermont and Georgia allow four stories and New York City, Seattle, and Honolulu have six-story limits. But the United States is an outlier. According to the Boston Indicators report, most other countries allow single-stair housing to higher heights: five stories in Japan and the United Arab Emirates, six stories in Scotland and Hong Kong, seven stories in the United Kingdom, and eight in Australia and New Zealand.
Of course, fire safety is vital. Brockton Fire Chief Brian Nardelli, second vice president of the Fire Chiefs Association of Massachusetts, said the materials used in household products today — like plastics and polyurethane — burn hotter and faster than the natural fibers that were historically used and release more toxic gases. “I do not feel comfortable with what’s burning in homes today that taking away a second egress … is warranted,” Nardelli said. The National Fire Protection Association has raised concerns about what happens if a single stairwell gets blocked by fire or smoke, and whether firefighting operations would be impeded if firefighters are climbing the same stairwell where residents are evacuating.
Massachusetts Fire Marshal Jon Davine, in a January 2025 newsletter from the Department of Fire Services, called allowing one stairwell for buildings up to six stories a “serious life safety hazard to occupants and first responders.” He said a second stairwell was critical in evacuating 20 people from an arson at a Plainville apartment building in November 2024.
However, the Pew study examined fire death rates in modern, single-stair, four- to six-story buildings in New York City, Seattle, and the Netherlands. The report found that fire death rates were comparable in single- and double-stair buildings, and the lack of a second stairway did not play a role in any of the four fire deaths over 12 years in New York and Seattle’s single-stair buildings.
Changes to the Massachusetts building code would involve nuanced decisions, and legislation pending in the state Legislature would create a commission to study the issue.
Raising the limit to four stories is a no-brainer: Of the two model building codes generally used in the United States, the NFPA code already puts the limit at four stories and up to 16 units, and the International Building Code is undergoing an amendment process that is expected to raise its limit from three to four stories. But there may be room for more leeway: the nonprofit Center for Building in North America suggests raising limits to six stories.
Any code revision will also have to determine what fire safety measures to require in single-stair buildings, like sprinklers, smokeproof enclosures, limits on distance to an exit, or use of specific construction materials or technologies.
While having a statewide building code makes construction simpler for developers, another question is whether to let municipalities impose stricter rules. For example, could a rural community with a tiny fire department impose a stricter height limit because of the longer time it takes firefighters to arrive?
For projects to get built, a developer has to make the finances work, and with high interest rates and rising construction costs, that’s getting harder and harder. The type of midsize apartment buildings that single-stair construction could unlock are exactly what the region needs.
Editorials represent the views of the Boston Globe Editorial Board. Follow us @GlobeOpinion.
