When the decision makers behind some of the biggest multifamily development projects in Boston consider what their signature towers will be made of, they increasingly lean toward concrete over the steel that long dominated the local construction industry.  

The developers of several significant recent downtown projects have chosen to build residential towers either completely or partially of concrete, maximizing the rentable space in their new properties.

In many cases, a concrete frame in a residential project can prove more economical than the steel that has for so long defined Boston’s skyline, despite higher up-front costs for the dense gray material.   

For one thing, the size of the structure comprising the frame of the building is reduced when a building is concrete, versus the massive steel beams comprising most office buildings in the city. That allows for thinner spaces between floors, which can allow for additional floors of rentable space in a building, according to Angus Leary, chief operating officer for Boston’s Suffolk Construction Co. In addition to the increased space, less noise reverberates through a concrete structure because the material is denser.

But there are advantages to be gained from building with steel. Steel is more elastic than concrete, so it can be more effective in areas with a greater risk of earthquakes, said Paul Martini, senior vice president for Commodore Builders. Plus, steel is more adaptable over time. It’s far easier to punch holes in a steel frame for alterations than a concrete one, said Matt Capone, sales manager for Schock, which creates insulating materials for commercial properties.  Another benefit is steel is more easy to use during winter months, since concrete needs to be temperate controlled while it’s being poured.

“If you can get the concrete foundation in … the steel is just bolted together and it goes up,” Martini offered.

Concrete is seldom used in office buildings in Boston because of the added costs. Concrete buildings can cost $5 to $8 more per square-foot, and that doesn’t factor in the changes needed for the foundation elements to support what will also be a heavier building, according to Suffolk’s Leary. But concrete is something of a new trend in Boston residential construction. With so few large new residential projects in the city until just a few years ago, there just weren’t many opportunities to utilize the material, he added.

It’s a Boston Thing

As one of the city’s busiest construction firms, Suffolk has built several of the newest residential buildings in the area. The Kensington near Downtown Crossing was a hybrid of a concrete core surrounded by steel, and 315 on A in the Fort Point district, along with Millennium Place downtown, were both built completely with concrete. And Millennium Tower, the 625-foot residential building that will rise from the ashes of the Filene’s department store downtown, will be built entirely with concrete.

Along with the Millennium Tower, developer Millennium Partners also recently built the similarly named Millennium Place condos. But Millennium is a New York-based real estate firm, and when it comes to building their residential projects, that fact shows.   

But Boston is typically a steel structure town, making it unique from much of the rest of the country, not just New York City, said Phil Casey, an associate principal with CBT Architects. One reason for that is that since Boston has been so traditionally steel, there are only so many companies with the experience of building with concrete, according to Casey.

“We can clad a building with anything. But from a planning perspective, concrete is a little less flexible than steel,” Casey opined.

But in New York, the rent structures are different from Boston, making concrete an affordable way to build, offered Suffolk’s COO Leary.

“It’s what they demand in that city,” Leary said.

What we see more of in Boston is the hybrid scheme. Buildings have concrete cores, the elevator shafts and stairways, but steel framing for the floors around the core.

“That way you get a stiffer, more efficient structure, with a little less bracing in the exterior, but still the flexibility of floor steel,” Casey offered.

Email: jcronin@thewarrengroup.com