Monadnock Building - Architecture

Architecture

Together, the two parts of the building have a frontage of 420 feet (130 m) on Dearborn Street with a depth of 70 feet (21 m). The original northern half presents a plain, unbroken vertical mass of purple-brown brick, which is contoured to create a gentle curve at the base of the building and an outward flare to form an austere parapet at the top. The gentle swelling at base and cornice, observed historian Donald Hoffman, "came very close to the bell-shaped column the Egyptians had derived from papyrus". The corners of the building are gracefully chamfered as they rise to the top and the oriel windows are chamfered at their base. The floor divisions are not marked on the exterior; the unbroken edifice is interrupted only by a series of cantilevered window bays, separated by rows of single thin silled windows set into the vertical face. The entryways are small, single-height portals topped with plain stone lintels.

The south half preserves the lines and color of the older building, but is vertically divided by a stringcourse over the second story, emphasizing the building's base, and a large ornamental copper cornice at the roof line. Massive blocks of red granite, 6 feet (1.8 m) thick, frame the large, two-story entrances. The projecting window bays of the original are repeated, but alternate in a pattern of two four-window bays to one recessed strip of windows to create the undulating appearance of the facade that was an early trademark of Holabird & Roche. Carl Condit, historian of the Chicago school, has commented that:

The general appearance of the Monadnock almost belies its masonry construction. The projecting bays of the walls with their large glass areas give the structure a light and open appearance in spite of its great mass.... Stripped of every vestige of ornament, its rigorous geometry softened only by the slight inward curve of the wall at the top of the first story, the outward flare of the parapet, and the progressive rounding of the corners from bottom to top, subtly proportioned and scaled, the Monadnock is a severe yet powerfully expressive composition in horizontal and vertical lines.

The Monadnock rests on the floating foundation system invented by Root for the Montauk Building that revolutionized the way tall buildings were built on Chicago's spongy soil. A 2-foot (0.61 m) layer of concrete, reinforced with steel beams, forms a spread footing extending out 11 feet (3.4 m) under the surrounding streets, spreading the weight of the building over a large area of earth. The building was designed to settle 8 inches (200 mm), but by 1905 had settled that much and "several inches more", necessitating reconstruction of the first floor. By 1948, it had settled 20 inches (51 cm), resulting in a step down from the street to the ground floor. The entire east wall is supported on caissons sunk to the hardpan, installed when the subway Blue Line was dug under Dearborn Street in 1940.

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 20 feet (6.1 m) wide and the south half corridors are 11 feet 6 inches (3.51 m). 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 600 square feet (56 m2), 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.