Cast Iron House, a new residential complex set in a 132-year-old building in TriBeCa, is commencing sales this month for its new duplexes and penthouses. The 13-unit project from Knightsbridge Properties melds modern interior design with a historic facade that includes more than 4,000 pieces of the building’s original cast iron, which was the material of choice for construction before the Industrial Revolution gave rise to steel production. It took the New York–based developers more than three years to remove …