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The Monadnock Building (historically the Monadnock Block), is a skyscraper located in the south Loop community area of Chicago, Illinois. The north half of the building was designed by the firm of Burnham & Root and built in 1891. The tallest commercial load-bearing masonry building ever constructed, it employed the first portal system of wind bracing in America. Its decorative staircases represent the first use of aluminum in building construction. The south half, constructed in 1893, was designed by Holabird & Roche and is similar in color and profile to the original, but the design is more traditionally ornate. When completed, it was the largest office building in the world. The building was remodelled in 1938 in one of the first major skyscraper renovations ever undertaken—a bid, in part, to revolutionize how building maintenance was done and halt the demolition of Chicago's aging skyscrapers. It was sold in 1979 to owners who restored the building to its original condition. The north half is an unornamented vertical mass of purple-brown brick, flaring gently out at the base and top, with vertically continuous bay windows projecting out. The south half is vertically divided by brickwork at the base and rises to a large copper cornice at the roof. Projecting window bays in both halves allow large exposures of glass, giving the building an open appearance despite its mass. The Monadnock is part of the Printing House Row District. It was one of the first buildings named a Chicago Architectural Landmark in 1958. It was added to the National Register of Historic Places in 1970, and named as part of the National Historic Landmark South Dearborn Street–Printing House Row North Historic District in 1976.