The narrow building allows an external exposure to all of the 300 offices, which pass natural light via double hung outside windows through feather-chipped glass transoms and hallway partitions into the single central corridor. Skylights bring sunlight into the open stairwells. The north half corridors are wide and the south half corridors are . In the north half, there are two open stairs in the center at the one third points, with perforated risers, white marble treads, and decorative steel railings. There are two banks of four elevators on the west side of the corridor, one for passengers and the other for freight. In the south half, there is a single bank of elevators on the north half of the length. The southern bank was abandoned and slabbed over on each floor. There is a flight of stairs behind each of these shafts with marble treads, closed cast iron risers, and ornamental balusters. The basic office suite is , consisting of one outer office and two or more inner offices. Heavy internal walls at the quarter and halfway points, the arches of which manifest Root's innovative wind bracing, mark the boundaries of the four original buildings.