The Willis Tower was the world’s tallest building for 25 years, and is the tallest building in North America. It is currently the second-tallest building in the world, and the world’s third-tallest structure. (The CN Tower in Toronto is the second-tallest structure in the world.) The tower was designed by Skidmore Owing and Merrill, and was the first structure to use the “bundled tube” design, which combined nine independent interior steel “tubes” that shared a single exterior superstructure. Most super-tall buildings use this basic design or a modification of it to achieve both height and stability.
The Willis Tower is 1,451 feet tall and offers 108 stories of office space. Television antennas on the roof extend the overall height of the building to 1,730 feet. Sears commissioned the building’s construction, although the tower – when complete – contained far more space than the retailer itself needed. Sears initially planned a smaller tower, but added floors to the design to provide opportunities for other tenants to lease space in the high-profile building. Sears sold the building to a Boston-based property management firm in 1994 and completely vacated the building in 1995.
In 1997, the building was sold to the same company that owned the CN Tower, and was the subject of a foreclosure in 2003. The name of the building was changed in 2009 to its current identity, the Willis Tower. The Willis Group, a UK-based insurance broker will hold the naming rights until at least 2024. The building was most recently sold in 2015 and the new owners have a number of plans to redevelop the property. Notably, the Willis Tower has never been fully occupied. It also survived a plan to paint the outside of the tower silver at a cost of $50 million. According to the owners at that time, the silver paint would have made the building more energy-efficient.
The Willis Tower has more than 16,000 tinted glass windows that give the building its signature bronze appearance. Six window-washing robots that are mounted on the roof clean the glass on all 108 floors. It also has an observation deck on the building’s 103rd floor. In 2009, four retractable glass-floored observation decks were added to the building that extend outward by about four feet.
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Photo Credit: Rob Young , via Flickr.com