While determining the world's tallest structure has generally been straightforward, the definition of the world's tallest building or the world's tallest tower is less clear. The disputes generally center on what should be counted as a building or a tower, and what is being measured.
In terms of absolute height, the tallest structures are currently the dozens of radio and television broadcasting towers which measure over 600 meters (about 2,000 feet) in height. There is, however, some debate about:
* whether structures under construction should be included in the list
* whether structures rising out of water should have their below-water height included.
For towers, there is debate over:
* whether guy-wire-supported structures should be counted
For buildings, there is debate over:
* whether communication towers with observation galleries should be considered habitable buildings.
* whether only habitable height is considered.
* whether roof-top antennas should be considered towards height of buildings; with particular interest in whether components that look like spires can be either classified as antennas or architectural detail.
These debates will likely lose some relevance in 2009, as the Burj Dubai, a building currently under construction in Dubai, United Arab Emirates, is planned to exceed all other existing above-ground structures in height, including guyed TV towers.
The tallest standing structure is the KVLY-TV mast 30 miles (48 km) north of Fargo, North Dakota United States, at 628.8 m (2,063 ft). It is a transmission antenna, consisting of a bare metal structure supported by guy-wires.
Transmission antennas of this type are not usually included with the world's tallest buildings because they are not self-supporting. The issue is further complicated if all manmade habitable structures are considered. Under that criterion it is possible to claim 'tallest structure' records for deep mine-shafts, or the Mohole drilling rig, which can be several miles (8-10 km) in vertical length.
The CN Tower in Toronto, Ontario, Canada, standing at 553.3 m (1,815 ft), was the world's tallest freestanding structure on land from 1976 until September 12, 2007, when it was overtaken in height by the rising Burj Dubai. The tower has the world's highest public observation deck at 446.5 m (1,465 ft). It remains the world's tallest completed freestanding structure.
The Petronius Platform stands 610 m (2,001 ft), leading some to claim it as the tallest freestanding structure in the world. However, as this oil and natural gas platform is partially supported by wires, critics argue that it is not freestanding, and the below-water height should not be counted, in the same manner as underground 'height' is not taken into account in buildings.
The Troll A platform is 472 m (1,549 ft), without any part of that height being supported by wires.
Taipei 101 in Taipei, Taiwan is currently the world's tallest inhabited building in three of the four main categories that are commonly measured: at 509.2 m (1,671 ft) as measured to its architectural height (spire) as well as roof height 449.2 m (1,474 ft) and highest occupied floor 439.2 m (1,441 ft). The Sears Tower is highest in the last category: the greatest height to top of antenna of any building in the world at 527.3 m (1,730 ft).
The Burj Dubai, currently under construction, is already the tallest freestanding structure on land. As of 5 February 2008, the tower's developers reported its height to be 604.9 m (1,985 ft) with 159 completed floors, surpassing Taipei 101 as the tallest skyscraper. On its completion, projected for 2009, it will break the height record in all four categories for completed buildings by a wide margin. While the final height has not been released to the public, Greg Sang, the construction manager, says that the building will rise to a minimum of 700 m (2,297 ft). The developer, Emaar, is keeping structural details secret due to competition for the "world's tallest" with other proposed structures, including the nearby Al Burj. The CN Tower will retain its record of the world's highest observation deck as Burj Dubai's deck will be at 442 m (1,450 ft). The 'Symbol of Dubai' will have more than 160 floors, 56 elevators, apartments, shops, swimming pools, spas and corporate suites.
Up until 1998 the tallest building status was essentially uncontested. Counting buildings as structures with floors throughout, and with antenna masts excluded, the Sears Tower in Chicago was considered the tallest. When the Petronas Twin Towers in Kuala Lumpur, Malaysia were built, controversy arose because the spire extended nine meters higher than the roof of the Sears Tower. Excluding the spire, the Petronas Towers are not taller than the Sears Tower. At their convention in Chicago, the Council on Tall Buildings and Urban Habitat (CTBUH) reduced the Sears Tower from world's tallest and pronounced it not second tallest, but third, and pronounced Petronas as world's tallest. This action caused a considerable amount of controversy, so CTBUH defined four categories in which the world's tallest building can be measured:
1. Height to the structural or architectural top (including spires and pinnacles, but not antennas, masts or flagpoles)
2. Height to the highest occupied floor
3. Height to the top of the roof
4. Height to the top of antenna
The height is measured from the pavement level of the main entrance. At the time, the Sears Tower held first place in the second and third categories. Petronas held the first category, and the original World Trade Towers held the fourth. Within months, however, a new antenna mast was placed on the Sears Tower, giving it hold of the fourth category. On April 20, 2004, the Taipei 101 in Taipei, Taiwan, was completed. Its completion gave it the world record for the first three categories. On July 21, 2007 it was announced that the Burj Dubai had surpassed Taipei 101 in height, reaching 512 m (1,680 feet) tall. However Burj Dubai is still under construction.
Today, Taipei 101 leads in the first category with 509 m (1,671 feet); in the second category with an occupied floor at 439 m (1,441 feet); and in the third category with 449 m (1,474 feet). The first category was formerly held by the Petronas Twin Towers with 452 m (1,483 feet), and before that by Sears Tower with 442 m (1,451 feet). The second and third categories were held by the Sears Tower, with 412 m (1,351 feet) and 442 m (1,451 feet) respectively.
The Sears Tower still leads in the fourth category with 527 m (1,729 feet), previously held by the World Trade Center until the extension of the Chicago tower's western broadcast antenna in 2000, over a year prior to the Trade Center's destruction in 2001. Its antenna mast included, 1 World Trade Center measured 526 m (1,727 feet). The World Trade Center became the world's tallest buildings to be destroyed or demolished; indeed, its site entered the record books twice on September 11, 2001, in that category, replacing the Singer Building, which once stood a block from the WTC site.
The Ostankino Tower and the CN Tower are excluded from these categories because they are not "habitable buildings", which are defined as frame structures made with floors and walls throughout.
WORLD'S TALLEST FREESTANDING STRUCTURE ON LAND
Freestanding structures include observation towers, monuments and other structures not generally considered to be "Habitable buildings", but excludes supported structures such as guyed masts and ocean drilling platforms.
The world's tallest freestanding structure on land is defined as the tallest self-supporting man-made structure that stands above ground. This definition is different from that of world's tallest building or world's tallest structure based on the percent of the structure that is occupied and whether or not it is self-supporting or supported by exterior cables. Likewise, this definition does not count structures that are built underground or on the seabed, such as the Petronius Platform in the Gulf of Mexico. Visit world's tallest structure by category for a list of various other definitions.
As of 5 February 2008, the tallest freestanding structure on land is the still under construction Burj Dubai in Dubai, United Arab Emirates. The building, which now stands at 604.9 meters (1,984.6 ft), surpassed the height of the previous record holder, the 553.33 meter (1,815 ft) CN Tower in Toronto, Ontario, on September 12, 2007. It is scheduled to be completed in 2009, and is planned to rise to a height of over 800 meters (2,625 ft).
FUTURE RECORD-BREAKING STUCTURES
Numerous supertall skyscrapers are in various stages of proposal, planning, or construction. Each of these, depending on the order of completion, could become the world's tallest building or structure in at least one category:
* Burj Dubai in Dubai, UAE is expected to be an 818 m (2,684 ft) tall skyscraper. It is currently under construction, and as of 5 February 2008, it is 604.9 m (1,984.6 ft) tall, with 159 completed floors. Upon completion (projected for 2009) this will be the tallest manmade structure of any kind in history. However, it might not hold that record for long; see the proposals section below.
* The Russia Tower, under construction in Moscow, Russia, is expected to be 612.2 m (2,009 ft) with 118 floors. Construction started in September 2007. When completed, it will be the tallest building in Europe, and the second tallest building in the world after the Burj Dubai.
* The Guangzhou TV & Sightseeing Tower, being built in Guangzhou, China, is expected to be 610 m (2,001 ft) tall.