When assessing the placings of structures, there is some debate about:
- whether a structure under construction should be included in the list
- whether a building or structure has to be officially opened before it is included on the list.
- whether structures rising out of water should have their below-water height included.
- what should be counted as a building or a tower, and what is being measured.
- for towers, whether guy-wire-supported structures should be counted.
For buildings, there is debate over:
- whether only habitable height is considered
- whether communication towers with observation galleries should be considered "habitable" in this sense
- whether rooftop antennas, viewing platforms or any other architecture that does not form floors, walls and rooms, i.e. not built as an occupiable room, should be considered towards height of building
- what would stop a room built on top of a telecommunications or viewing tower from changing the tower's class to that of "building"
- why a building that is not officially opened should be excluded from the ranks of tallest buildings
- what counts as an official opening
This category does not require the structure be "officially" opened.
The tallest man-made structure is Burj Khalifa, a skyscraper in Dubai that reached 829.84 m (2,723 ft) in height on January 17, 2009. By April 7, 2008 it had been built higher than the KVLY-TV mast in North Dakota, USA. That September it officially surpassed Poland's 646.38 m (2,120.7 ft) Warsaw radio mast, which stood from 1974 to 1991, to become the tallest structure ever built. Guyed lattice towers such as these masts had held the world height record since 1954.
The CN Tower in Toronto, Canada, standing at 553.3 m (1,815 ft), was formerly the world's tallest completed freestanding structure on land. Opened in 1976, it was surpassed in height by the rising Burj Khalifa on September 12, 2007. It has the world's second highest public observation deck at 446.5 m (1,465 ft).
The Petronius Platform stands 610 m (2,000 ft) 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 discounted in the same manner as height below ground is ignored on buildings. The Troll A platform is 472 m (1,549 ft), 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 1,000 m (3,300 ft) 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 theUrsa tension leg platform as the tallest structure in the world with a total height of 1,306 m (4,285 ft). The Magnolia Tension-leg Platform in the Gulf of Mexico is even taller with a total height of 1,432 m (4,698 ft).
Taipei 101 in Taipei, Taiwan, set records in three of the four skyscraper categories at the time it opened in 2004; at the time the Burj Khalifa opened in 2010 it remained the world's tallest inhabited building 509.2 m (1,671 ft) as measured to its architectural height (spire). The height of its roof 449.2 m (1,474 ft) and highest occupied floor 439.2 m (1,441 ft) had been surpassed by the Shanghai World Financial Center with corresponding heights of 487 m (1,598 ft) and 474 m (1,555 ft) respectively. Willis Tower (formerly Sears Tower) was highest in the final category: the greatest height to top of antenna of any building in the world at 527.3 m (1,730 ft).
Burj Khalifa broke the height record in all four categories for completed buildings by a wide margin. The Shanghai World Financial Center had the world's highest roof, highest occupied floor, and the world's highest public observation deck at 474.2 m (1,556 ft). It retains the last record, as Burj Khalifa's official observation deck will be at 442 m (1,450 ft).
Notable mentions include the Pharos (lighthouse) of Alexandria, built in the third century BC and estimated between 115–135 m (383–440 ft). It was the world's tallest non-pyramidal building for many centuries. Another notable mention includes the Jetavanaramaya stupa inAnuradhapura, Sri Lanka, which was built in the third century, and was similarly tall at 122 m (400 ft). These were both the world's tallest or second tallest non-pyramidal buildings for over a thousand years.
The tallest secular building between the collapse of the Pharos and the erection of theWashington Monument may have been the Torre del Mangia in Siena, which is 102 m (335 ft) tall, and was constructed in the first half of the fourteenth century, and the 97 m (318 ft) tallTorre degli Asinelli in Bologna, also Italy, built between 1109 and 1119.