<P> 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 . </P> <P> 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 m), 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 . </P> <P> The Monadnock belongs to the Printing House Row District, a National Historic Landmark which includes the Manhattan Building, the Old Colony Building, and the Fisher Building, some of Chicago's seminal early skyscrapers . The Manhattan Building, built by William LeBaron Jenney in 1890, was the first building in Chicago with a complete steel skeleton or "Chicago" construction, an innovation Jenney had introduced in the Home Insurance Building in 1884 . The first 16 - story building in America, at the time it was "regarded with awe and fear". Jenney's masterpiece, the Manhattan was considered a technical triumph in construction . The 17 - story Old Colony, built by Holabird & Roche in 1894, was considered one of the structural masterpieces of its time for its revolutionary portal form of bracing . It is the only survivor of a group of Chicago school buildings with rounded corner bays . The Fisher Building, built by Burnham in 1894, was an engineering miracle--the first tall commercial building to be built almost entirely without bricks . Its steel frame and thin terracotta curtain wall allowed two - thirds of the surface to be covered with glass . </P> <P> The district overlaps geographically with the Printer's Row neighborhood, originally the center of Chicago's printing and publishing industry, but now mostly converted to residential housing . The area is also home to the largest public library in the world, the Harold Washington Library, named for Chicago's first African - American mayor, and the Loop campus of Depaul University, America's largest Roman Catholic university . </P>

Who designed the first truly modern skyscraper using steel framework covered in masonry