Form and facade Each of the "tubes" is a column-free module measuring , which set back at different stories. There are setbacks at the 50th, 66th, and 90th floors. The lowest 50 stories contain nine tubes and cover each. The northwest and southeast tubes terminate at the 50th floor. The 51st through 66th floors each span , above which the northeast and southwest tubes end. From the 67th to 90th floors, each story is shaped like a cross, covering . The north, east, and south tubes end at the 90th floor; the remaining west and center tubes reach 108 floors, with an area of on each of the top stories. thumb|right|Sculpture honoring Fazlur Rahman Khan, considered the father of tubular designs, at the Willis Tower. Khan is known for making important advancements in skyscraper engineering. The Sears Tower was the first building to use this innovative design. It was both structurally efficient and economic: at 1,450 feet, it provided more space and rose higher than the Empire State Building and cost much less per unit area. The system would prove highly influential in skyscraper construction and has been used in most supertall buildings since, including the world's current tallest building, the Burj Khalifa. In February 1982, two television antennas were added to the structure, increasing its total height to . The western antenna was later extended, bringing the overall height to on June 5, 2000, to improve reception of local NBC station WMAQ-TV.
Form and facade Each of the "tubes" is a column-free module measuring , which set back at different stories. There .are setbacks at the 50th, 66th, and 90th floors. The lowest 50 stories contain nine tubes and cover each The northwest and southeast tubes terminate at the 50th floor. The 51st through 66th floors each span , above which the northeast and southwest tubes end. From the 67th to 90th floors, each story is shaped like a cross, covering . The north, east, and south tubes end at the 90th floor; the remaining west and center tubes reach 108 floors, with an area of on each of the top stories. thumb|right|Sculpture honoring Fazlur Rahman Khan, considered the father of tubular designs, at the Willis Tower. Khan is known for making important advancements in skyscraper engineering. The Sears Tower was the first building to use this innovative design. It was both structurally efficient and economic: at 1,450 feet, it provided more space and rose higher than the Empire State Building and cost much less per unit area. The system would prove highly influential in skyscraper construction and has been used in most supertall buildings since, including the world's current tallest building, the Burj Khalifa. In February 1982, two television antennas were added to the structure, increasing its total height to . The western antenna was later extended, bringing the overall height to on June 5, 2000, to improve reception of local NBC station WMAQ-TV.