Energy-saving windows and doors usually aren’t the most newsworthy updates in a historic preservation, but two such solutions completed as part of the critical 10-year preservation of St. Patrick’s Cathedral in New York City a couple of years ago warrant careful review for their elegant simplicity.

Asked to find an energy-efficient way to keep the cathedral’s 9,000-pound bronze doors open during visiting hours, Murphy Burnham & Buttrick Architects (MBB), the firm leading its preservation, designed transparent glass insertions to enable the practice without obstructing the church’s inspiring architecture. The MBB team understood that the doors are left open because “the entrance is symbolic of core congregation values of openness, welcome, and a sense of refuge,” explains MBB partner Jeffrey Murphy. Still, leaving them ajar had previously led to an expensive loss of conditioned air and energy. The solution: MBB worked with Silman and Eckersley O’Callaghan Engineers and glass manufacturer Seele, to devise massive transparent glass pocket doors that slide open and closed using Vitrocsa's Invisible Wall System. Now, at the push of a button, the panels slide within floor channels and vanish into the new interior wall MBB built out to house them. With the original bronze doors open, the clear-glazed entry looks virtually unobstructed.