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 by height to roof
This list of tallest buildings in the world by height to roof ranks completed skyscrapers by height to roof which reach a height of 350 metres (1,148 ft) or more. Only buildings with continuously occupiable floors are included, thus non-building structures including towers, are not included. Some assessments of the tallest building use 'height to roof' to determine tallest building in the world, as 'architectural feature' is regarded as a subjective and an imprecise comparative measure. However, in November 2009, the CTBUH stopped using the roof height as the metric for tall buildings because modern tall buildings rarely have a part of the building that can categorically be deemed the roof.