When first considering the addition of floors at a former South Boston rivet factory in 2018, the nonprofit owner CIEE Inc. quickly realized that installing a heavy concrete or steel system on top of the existing mass masonry heavy timber building would require significant work on the 120-year-old building’s foundation. Various bar joist and concrete solutions involved cost-prohibitive foundation upgrades to handle the added structural load.

Designers eventually suggested cross-laminated timber (CLT) for the future mixed-use building because it is nearly 70% lighter than concrete. “This was a no-brainer because it led to no foundation upgrades, except where we were adding an elevator core,” says Bryan Maltais, senior project manager for the project’s engineer of record, Boston-based McNamara Salvia Structural Engineers.