Sears Tower

The Sears Tower is a skyscraper in Chicago, Illinois. It has been the tallest building in the United States since 1973, surpassing the World Trade Center, which itself had surpassed the Empire State Building only a year earlier. Commissioned by Sears, Roebuck and Company, it was designed by chief architect Bruce Graham and structural engineers Srinivasa and Fazlur Khan of Skidmore, Owings and Merrill.

Construction commenced in August 1970 and the building reached its originally anticipated maximum height on May 3, 1973. When completed, the Sears Tower had overtaken the roof of the World Trade Center in New York City as the world's tallest building. The tower has 108 stories as counted by standard methods, though the building owners count the main roof as 109 and the mechanical penthouse roof as 110. The distance to the roof is 442 m (1,450 ft 7 in), measured from the east entrance.

In February 1982, two television antennas were added to the structure, increasing its total height to 520 m (1,705 ft). The western antenna was later extended to 527 m (1,730 ft) on June 5, 2000 to improve reception of local NBC station WMAQ-TV.

Black bands appear on the tower around the 29th–33rd, 64th–66th, 88th–90th, and 104th–109th floors. These are louvers which allow ventilation for service equipment and obscure the structure's belt trusses which Sears Roebuck did not want to be visible as on the John Hancock Center. The Sears Tower has the second most total floor space of any building in the United States, only behind The Pentagon.

The building's official address is 233 South Wacker Drive, Chicago, Illinois 60606.

On August 12, 2007, the Burj Dubai in Dubai, United Arab Emirates was reported by its developers to have surpassed the Sears Tower in all height categories. It overtook the Sears Tower antenna (527.3m) and the building now currently stands at least 37.6 metres taller (564.9m).

In 1969 Sears, Roebuck & Co. was by far the largest retailer in the world, with about 350,000 employees. Sears executives decided to consolidate the thousands of employees in offices distributed throughout the Chicago area into one building on the western edge of Chicago's Loop. With immediate space demands of 3 million square feet (279,000 m²), and with predictions and plans for future growth necessitating even more space than that, architects for Skidmore knew that the building would be one of the largest office buildings in the world.

Sears executives decided early on that the space they would immediately occupy should be efficiently designed to house the small army that was their Merchandise Group. However, floor space for future growth would be rented out to smaller firms and businesses until Sears could retake it. Therefore, the floor sizes would need to be smaller, and to have a higher window-space to floor-space ratio, to be more attractive and marketable to these prospective lessees. Smaller floor sizes necessitated a taller structure. Skidmore architects proposed a tower which would have large 55,000-square-foot (5,000 m²) floors in the lower part of the building, and would gradually taper the area of the floors down in a series of setbacks, which would give the Sears Tower its distinctive, husky-shouldered look.

As Sears continued to offer optimistic projections for future growth, the tower's proposed height soared into the low hundreds of floors and surpassed the height of New York's unfinished World Trade Center to become the world's tallest building. Restricted in height not by physical limitation or imagination but rather by a limit imposed by the Federal Aviation Administration to protect air traffic, the Sears Tower would be financed completely out of Sears' deep pockets, and topped with two antennas to permit local television and radio broadcasts. Sears and the City of Chicago approved the design, and the first steel was put in place in April 1971. The structure was completed in May 1973. Construction costs totaled approximately $175 million USD at the time, which would be equivalent to roughly $950 million USD in 2005. For comparison, Taipei's Taipei 101, built in 2004, cost around the equivalent of US$1.64 billion in 2005 dollars.