Vanity height is the distance between a building's highest floor and its architectural top, not counting antennae, flagpoles or other functional extensions. The CTBUH finds that supertall buildings have used such uninhabitable extensions for about 30 percent of their height on average, which raises questions about how to define and rank them. CTBUH floor counts can differ from other published accounts. Some regions skip certain floor numbers, such as 4, 14 and 24 in Hong Kong, and an owner or marketing team may number floors to meet its own goals instead of showing the physical floors present in the building. For the CTBUH to call a building completed, it must be topped out both structurally and architecturally, fully clad, and open for business or at least partly occupiable. A building is topped out structurally when the highest element of its main frame is in place, and architecturally when the spire and parapets are also in place.

The CTBUH lists a proposed building only if a credible source, such as a formal press release or a city planning application, has verified it. Because early designs change and clients limit information, a proposal's height is always unconfirmed until detailed design and construction begin. A building also has to be a single building to count. The CTBUH treats a tower as a single, co-joined building when 50 percent or more of its total height is connected, and as a single-function building when 85 percent or more of its height is used for one function. The Burj Khalifa is built of steel over concrete: the bottom has a reinforced concrete core, columns and floors, and the top has steel columns and steel beams. It has 163 floors above ground and 58 elevator cars, with a top elevator speed of 10 meters per second.

The Burj Khalifa used 330,000 cubic meters of concrete and 55,000 tonnes of steel rebar, and construction took 22 million man-hours. Its foundation holds 192 piles, each 1.5 meters across and 43 meters long, buried more than 50 meters deep, and was designed to support a building weighing about 450,000 tonnes. The Burj Khalifa's concrete was not poured during the day. In summer, builders added ice to the mix and poured at night, when the air was cooler and more humid, because cooler concrete cures more evenly and is less likely to set too quickly and crack. The Burj Khalifa has 27 setbacks in a spiral pattern, arranged to reduce the wind vibration caused by eddies and vortices. At its tallest point, the tower sways a total of 1.5 meters (4.9 feet).

Tall buildings can use their own height. At the Burj Khalifa, cooler air, lower air density and lower humidity at the top allow for sky-sourced fresh air that takes less energy to cool and dry. Its elevators can also be used under controlled conditions for evacuation, which cuts total evacuation time by 45 percent compared with stairs alone. Taipei 101's elevators held the record as the world's fastest when it opened, moving riders from the 5th floor to the 89th floor in 37 seconds at 60.6 kilometers per hour. Shanghai Tower's elevators later reached 20.5 meters per second until the Guangzhou CTF Finance Center passed them in 2017 at 21 meters per second. Fazlur Rahman Khan, a structural engineer from Bangladesh who worked at Skidmore, Owings and Merrill in Chicago, introduced the tube system, in which a building acts like a hollow cylinder to resist lateral loads such as wind, earthquakes or impact. The first example of the tube was the 43-story DeWitt-Chestnut apartment building in Chicago, finished in 1966.

In the tube system the outside wall carries the wind load. Closely spaced columns on the perimeter are tied together with deep beams to form a rigid frame, which amounts to a dense, strong structural wall. That lets the interior be framed just for gravity loads, with few columns, located at the core. Most buildings of more than 40 stories built since the 1960s use this type. On 8 August 2019, the tuned mass damper in Taipei 101 moved 15 centimeters during an earthquake, according to the building's management. Taipei 101 also rises in eight-story modules, and the top of each module houses mechanical floors with ventilation, water storage and other services. As of October 2026, Dubai has the most supertall or taller buildings of any city, at 33, followed by Shenzhen with 22 and New York City with 18. China has 138 of them, the most of any country, followed by the United Arab Emirates with 38 and the United States with 34.

Words to know

• topped: reached the top
• parapets: low roof walls
• piles: deep foundation posts
• lateral: sideways