A structural failure has delayed a major office-to-residential conversion project in midtown Manhattan after two columns buckled inside the building under renovation.

The project aims to transform two office buildings—one built in 1909 and the other in the 1960s—into approximately 1,600 apartments. The plans include adding more than a dozen floors to the older building and redesigning and expanding the newer structure.

The column failure occurred on the 21^st floor of the newer building on July 7. Construction crews installed temporary supports as city officials and engineers investigate the cause.

Early assessments point to additional structural loads as a possible factor. Ben Schafer, a structural engineering professor at Johns Hopkins University, and Emily Guglielmo, a San Francisco-based structural engineer, told ABC News the added weight from the renovation likely contributed to the failure.

Guglielmo said the original design assumptions may have been misunderstood, or construction crews may have overloaded or weakened the structure.

She added that a combination of robust building codes, inspections, and experienced construction crews makes failures rare. “We’re privileged to have really robust building codes that explain to us as engineers how to do our designs in a way that’s safe,” she told ABC News.

Officials deemed the structure stable after workers added temporary supports from the ninth floor through the roof. They also used large quantities of pipe columns to support the structure.

Developer speaks

MetroLoft is the project’s developer. Founder and principal Nathan Berman said the issue concerns the building’s structural capacity, not the office conversion itself. “It’s not a design issue,” Berman told CBS. “This issue is strictly structural. We put more load on the columns than they could support.”

Berman said crews reinforced most of the building’s columns but may have missed the two columns that later buckled.

“We may have not reinforced them properly, or we may have missed them,” he told CBS.