CN Tower
"Guinness World Records" has called the CN Tower "the world's tallest self-supporting tower" and "the world's tallest free-standing tower". Although Guinness did list this description of the CN Tower under the heading "tallest building" at least once, it has also listed it under "tallest tower", omitting it from its list of "tallest buildings." In 1996, Guinness changed the tower's classification to "World's Tallest Building and Freestanding Structure". Emporis and the Council on Tall Buildings and Urban Habitat both listed the CN Tower as the world's tallest free-standing structure on land, and specifically state that the CN Tower is not a true building, thereby awarding the title of world's tallest building to Taipei 101, which is shorter than the CN Tower. The issue of what was tallest became moot when Burj Khalifa, then under construction, exceeded the height of the CN Tower in 2007 (see below).
World Trade Center (1973–2001)
When completed in 1972, 1 World Trade Center became the tallest building in the world for two years, surpassing the Empire State Building after a 40-year reign. The North Tower stood tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood tall. With the -tall antenna/mast, the highest point of the North Tower reached . Chicago's Sears Tower, finished in , reached at the rooftop. Throughout their existence, the WTC towers had more floors (at 110) than any other building. This number was not surpassed until the advent of the Burj Khalifa, which opened in 2010. Each tower had a total mass of around 500,000 tons.