The former home of the New York Stock Exchange, which became home to more than 500 housing units for New Yorkers, is facing default.

The Financial District office tower at 20 Broad St. was converted into housing by Nathan Berman’s Metro Loft Management several years before the pandemic.

But the $250M mortgage tied to the property comes due in September, and the firm “has indicated it was unable to repay the loan at its maturity,” according to bond rating firm KBRA, as first reported by Crain’s New York Business.

The loan, set to mature Sept. 9, was transferred to a special servicer earlier this month, according to commentary on Morningstar Credit’s dashboard.

The apartment building has 533 units and ground-floor retail. The apartment portion of the building is more than 95% occupied but has suffered from offering concessions, according to July commentary on Morningstar. In this case, tenants were offered one month free for 12-month leases or two months free for 14-month leases.

“Existing rent concessions are biggest driver of depressed cash flow but is expected to improve over the next six months,” the servicer commentary says.

The building’s retail space is 46% leased. That is expected to rise with new leases in the works, according to the servicer.

Metro Loft requested a short-term extension on its 2019 mortgage but was denied, according to Crain’s.

Berman has been crowned the king of conversions, but obstacles remain with the practice. Less than 1 in 6 buildings across the country are quality candidates, with many failing to meet light, ventilation and plumbing requirements for residential use. It can also be expensive, forcing some owners to consider demolitions to start over from scratch.

20 Broad St.'s financial troubles could be a lesson for landlords looking to residential conversions as a solution to vacated office stock.

Housing is desperately needed in the city, where vacancy hit 1.4% earlier this year, but conversions can result in oddly shaped apartments. That can drive high-paying renters to look elsewhere.

A Bloomberg report last year documented such issues at 20 Broad St. and 63 Wall St., another Berman conversion that sold in 2016.

“The building was really big, and it did feel almost office-like, not super-communal or homey,” a 63 Wall St. resident told Bloomberg. “They tried their best to turn it into a beautiful, grand luxury building, but I lived in a studio, and it was a very awkward space. It wasn’t square, it wasn’t a rectangle, it had all kinds of bizarre edges and weird corners.”