The Phillips Exeter Academy Library at Phillips Exeter Academy in Exeter, New Hampshire is the largest secondary school library in the world. Its most notable feature is a dramatic atrium with enormous circular openings that reveal several floors of book stacks.
Kahn accordingly made the building's exterior relatively undramatic, suitable for a small New England town. Its facade is primarily brick with teak wood panels at most windows marking the location of a pair of wooden carrels. The corners of the building are chamfered (cut off), allowing the viewers to see the outer parts of the building's structure. A shadowed arcade circles the building on the ground floor.
A circular double staircase built from concrete and faced with travertine greets the visitor upon entry into the library. At the top of the stairs the visitor enters a dramatic central hall with enormous circular openings that reveal several floors of book stacks. At the top of the atrium, two massive concrete cross beams diffuse the light entering from the clerestory windows. Because the stacks are visible from the floor of the central hall, the layout of the library is clear to the visitor at a glance, which was one of the goals the Academy's building committee had set for Kahn.
The central room is 52 feet (15.8 m) high, as measured from the floor to the beginning of the roof structure, and 32 feet (9.8 m) wide. Those dimensions approximate a ratio known as the Golden Section, which was studied by the ancient Greeks and has been considered the ideal architectural ratio for centuries. The circle and the square that are combined so dramatically in the atrium were considered to be the perfect geometric units by the ancient Roman architect Vitruvius. He also noted that the human body is proportioned so that it can fit in both shapes, a concept that was famously expressed with a combined circle and square by Leonardo da Vinci in his drawing Vitruvian Man.
The placement of carrel spaces at the periphery was the product of thinking that began years earlier when Kahn submitted proposals for a new library at Washington University. There he dispensed with the traditional arrangement of completely separate library spaces for books and readers, usually with book stacks on the periphery of the library and reading rooms toward the center. Instead he felt that reading spaces should be near the books and also to natural light. For Kahn, the essence of a library was the act of taking a book from a shelf and walking a few steps to a window for a closer look: "A man with a book goes to the light. A library begins that way. He will not go fifty feet away to an electric light". Each carrel area is associated with two levels of book stacks, with the upper level structured as a mezzanine that overlooks the carrels. The book stacks also look out into the atrium.