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Theoretical skyscraper height is limited by wind, elevators, and budget, not structural materials. Counterweights and multiple stems can help with wind, while double-deck elevators and sky lobbies can improve elevator efficiency. Budget is the ultimate limitation, with a 6,500-foot structure potentially costing $10 billion USD. Frank Lloyd Wright’s 1 mile tall tower, The Illinois, was designed in 1956 but never built.
For a long time, engineers and architects have speculated about how tall a skyscraper could theoretically be. Frank Lloyd Wright, considered the greatest American architect of all time, designed a 1 mile (1.73 km) tall tower, The Illinois. This tower was to be built in Chicago and had 528 floors. It was designed in 1956 and probably could have been built then, but at great expense.
Structural materials are not the main limiting factor on building height. Very tall buildings are often surprisingly light for their size; after all, they’re mostly empty spaces. Steel is strong enough to support structures 6.2 miles (10 km) or taller, while advanced composites could support buildings reaching 62 miles (100 km) or more.
The three main limitations on skyscraper height are wind, elevators, and budget.
A table of altitude versus maximum wind speed looks something like this, for a calm day in a temperate zone:
altitude
Maximum wind speed
2 km (1.24 mi)
Mph 22
4 km (2.28 mi)
Mph 56
6 km (4.52 mi)
Mph 90
8 km (4.97 mi)
Mph 134
10 km (6.21 mi)
Mph 179
12 km (7.46 mi)
Mph 200
Above an altitude of about 7.45 miles (12 km), the wind calms down. Also noteworthy is that the air thins with increasing altitude, slightly decreasing the load of intense winds. At the top of Mt. Everest, at just under 5.5 miles (~9 km altitude), the air is about four times thinner than at sea level.
Special design features are required to counteract the force of the wind on skyscrapers higher than approximately 500 feet (195 m). These can include large internal counterweights, made of metal or even pools of water, which move to redistribute weight towards the center of the building. Buildings made up of multiple stems, such as the Empire State Building in New York and the Burj Khalifa in the United Arab Emirates, are also good at dissipating wind.
Improvements in concrete’s load-bearing capacity have recently enabled the use of this rigid substance as a building material for very tall buildings, offering windproof luxuries not available with steel alone. The Ryugyong Hotel in North Korea, although never finished, would be an example of using concrete as a building material for this type of structure. The problems with the wind will certainly be challenging, but not unsolvable.
The lift factor is another major limitation of height. The taller the building, the more people live and work in it, and the more ground floor space must be used for elevators. This challenge was met with two strategies: using double-deck elevators and using sky lobs as intermediate points for elevator travellers. By using sky lobes as local elevators for small sections of the building, a dozen or more elevators could share a single shaft, greatly improving efficiency. For very tall buildings over 6,500 feet (2 km) or so, it may be necessary to use multi-level elevators, such as 5-story elevators. Otherwise, the entire ground floor is dominated by lifts.
The last major limitation to skyscraper size is, of course, budget. Burj Khalifa, the current tallest building in the world with a height of 2,717 feet (828m), costs about $4 billion US dollars (USD). Assuming costs scale linearly with increasing height (a generous assumption), building a 6,500-foot (2km) tall structure could cost $10 billion USD. This is probably around the limits of what developers would be willing to spend on a single project, although only time will tell.
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