Castle Square Apartments has been awarded LEED for Homes Multifamily Platinum Certification by the U.S. Green Building Council, after completing the nation’s largest deep energy retrofit of an existing affordable housing community.

Located on Tremont Street in Boston’s South End and constructed in the 1960s, Castle Square Apartments is a 540,000-square-foot mixed-use property comprised of 500 affordable apartment units and 20,000 square feet of retail space. LEED Platinum Certification was awarded upon completion of the two-year renovation.

The Castle Square Tenants Organization retrofitted its building with help from Winn Development and reduced energy consumption by 72 percent.

"Winn is very proud to have received such a significant recognition for the groundbreaking renovations we completed with Castle Square Tenants Organization," Larry Curtis, president of WinnDevelopment, said in a statement.