In terms of new architecture, Audubon Terrace—on Broadway between West 155th and 166th streets in Upper Manhattan—hasn’t seen much action since the 1930s, when the American Numismatic Society added a west wing to its facility. That addition completed a stately procession of Beaux Arts buildings filling nearly an entire city block and housing over the years such eclectic institutions as the American Geographical Society, the Museum of the American Indian, and the Hispanic Society of America.

But the long fallow spell has come to an end with a gleaming bit of modernism. The American Academy of Arts and Letters, whose McKim, Mead & White–designed headquarters punctuates the far end of the terrace, has installed an all-glass corridor, designed by architect James Vincent Czajka in consultation with Pei Cobb Freed & Partners (PCF), which links its walls with those of the Numismatic Society next door.

The Academy reached into its endowment and purchased the neighboring building in 2005, when the coin collectors moved downtown. The idea was to expand the institution’s curatorial, exhibition, and administrative space, all of which were overstuffed from more than 100 years of constant output by its members.

The two buildings shared a common wall on their first two levels, but the designers chose to create a passageway between them at the third, or terrace, level (there is a significant grade change between 155th Street and the mid-block terrace), where the gallery spaces already existed. At the terrace, however, there is a 12-foot gap between the Numismatic building and the Academy.

McKim, Mead & White left this space both to distinguish its structure from the otherwise cheek-by-jowl architectural ensemble as well as to create a sense of arrival at the end of the terrace. Wanting to preserve this effect, Czajka and PCF decided to build their passageway entirely out of transparent glass.

Glass has been de rigueur for this project type at least since I.M. Pei dropped several glistening pyramids into the courtyard of the Louvre in 1989. Fittingly, when Henry Cobb, the Academy’s current treasurer, offered his firm’s services pro bono for the link, he put Michael Flynn in charge—the very man who completed the controversial additions to France’s premier art museum. Unlike the pyramids, however, the link is extremely simple in construction.

The structure is composed almost entirely of seven pieces of low-iron laminated glass. It goes together like this: Three 1-inch-thick glass beams insert into and bear directly on the existing masonry walls. At the juncture between wall and beams is a U-shaped steel structure capped with bronze, which runs across the top of the beams and then down to the ground, serving as both a gutter and as a support for the glass. Atop the beams rest two 1-inch-thick glass panels, which slant toward the masonry walls and form the roof. Finally, two 10-foot-wide by 16-foot-high glass panels, each 1-inch thick, fit into the steel channel and form the link’s walls.

There is almost no tolerance between these elements, and being glass, there could be no trimming on site—everything had to fit together perfectly. In spite of these challenges, the assembly went smoothly in one six-hour period, with one crawler crane in the street and about 20 ornamental ironworkers from Rockland County–based W&W Glass.

As simple and nearly invisible as it is, this little structure goes out of its way to fit in with the classical architectural context. The 10-by-16-foot wall panels, for example, are precise golden rectangles—the ratio of the long side to the short side is 1.6180339887, the golden ratio, also known as the divine proportion, which is found throughout nature and which architects and artists during the Renaissance believed to possess the mystical imprimatur of God. (One could assume that working this element of heavenly symmetry into the project was Flynn’s way of firing back at the Paris newspapers and the well-known author Dan Brown, who falsely alleged that the Louvre pyramid is composed of 666 glass pieces.)

In addition, the pitch of the glass roof matches exactly the pitch of the pediment above the Academy’s nearest window. Angling the slope of the roof toward the masonry walls also mitigates streaking across the glass walls by directing runoff to the bronze gutter system. The designers applied a 50-percent, 1/8-inch ceramic frit to the roof panels to help conceal the inevitable water spotting, as well.

The floor of the link is also glass—16 laminated panels with white interlayers—and can be lit from beneath. The concept for this detail was arrived at somewhat by accident. Czajka hired a Pratt student to build a physical model for presentation to the client, but it came out looking rather dull, so they rigged a Christmas light into its base to show everyone how light-filled the space would be. When Henry Cobb saw the model he reportedly said, “Well that’s it. We need a glass floor. This baby needs to glow.”

A video of the addition’s installation can be found on the A/N Blog.