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).
List of tallest buildings and structures
The Petronius Platform stands off the sea floor leading some, including "Guinness World Records" 2007, to claim it as the tallest freestanding structure in the world. However, it is debated whether underwater height should be counted, in the same manner as height below ground is ignored on buildings. The Troll A platform is , without any part of that height being supported by wires. The tension-leg type of oil platform has even greater below-water heights with several examples more than deep. However, these platforms are not considered constant structures as the vast majority of their height is made up of the length of the tendons attaching the floating platforms to the sea floor. Despite this, "Guinness World Records" 2009 listed the Ursa tension leg platform as the tallest structure in the world with a total height of . The Magnolia Tension-leg Platform in the Gulf of Mexico is even taller with a total height of .