The Interior Library occupies the entire Wing 1100 West, including parts of the floors above and below and the hyphen (Technical Services Office, Room 2262) connecting Wings 2100 and 2200 West.
The fourth tier of the Stacks is on the same level as the Reading Room and is roughly seven bays long and five bays wide. Along the north wall of the Stacks is a long narrow Training Room with access from both the stacks and Card Index Alcove. Along the outer bay on the south side, extending the full length of the Stacks, is a series of Library staff offices.
The walls of the Reading Room are Indiana Limestone in regular, ahslar pattern. The only embellishments of the limestone walls are a simple molded cornice at the Balcony level and the capitals of the piers. In the four corners of the Reading Room are custom designed bookcases. The walnut bookcase is framed with simple piasters on the corners, crowned with a classical cornice, and supported on a ventilation cabinet with bronze grille of a modified Roman grate design. The bookcase is built-in with black marble base that matches the wall base of the Reading Room.
Hinged ornate bronze grilles cover the windows in the blind galleries over the Card Index Alcove and the Reference Alcove. The design of the grilles is a modified Roman grate design similar to the grilles in the Interior Auditorium. However, the grilles of the Library have anthemions radiating from the discs at the crossing of the X, instead of acanthus leaves.
The stairs leading to both Balconies are made of Cardiff green marble, honed finish treads and risers. The stairs railing is bronze. The design consists of a series of X's inscribed in vertical parallelograms. An arrow with head up pierces the intersection of the X. A running Greek fret design skirts the top of the railing just below the walnut handrail. The newel is a plain column with an acanthus capital.