By 2050, 75% of us will be living in cities, which means that building into the clouds is a serious business.

The projected 1km-high building in Jeddah, Saudi Arabia is set to be the world’s tallest, but what’s interesting is that it was meant to be a kilometre-and-a-half. So what’s stopping us from going higher?

The first major problem is wind: what feels like a gentle breeze at ground level can feel like a howling gale 500m up – as engineer William LeMessurier found out in 1978 when he just completed the 278m Citicorp Center in New York.

An undergraduate architecture student asked him whether the building could blow over in the wind, and LeMessurier discovered to his horror that the design had accounted for perpendicular winds, but not winds angled at 45 degrees to the building.

Workmen were sent in at night to make the building safe by welding steel plates to the wind braces, and this was kept a secret from the public for nearly 20 years.

These days, ingenious solutions are used to wind-proof skyscrapers, like the Taipei 101 in Taiwan. It’s topped off with a giant pendulum that swings in the opposite direction to the wind when a typhoon strikes.

Skyscrapers also need a big base, which limits their space saving potential. Dubai’s 828m-tall Burj Khalifa Tower offers a clever solution. A unique Y-shaped design with a hexagonal core and three wings has been used to create perfect stability.

The biggest problem, though? Elevators. Technologically, designers and engineers have hit the ceiling, and we have no solution yet. The issue is that cables longer than 600m are simply too heavy to winch. So, until we can solve this, the dream of the 5km-high megatower will remain a fantasy.

Source: BBC Future

See also: 

Saudi Arabia is building the world’s tallest tower

Shanghai Central Tower world’s second tallest building at 2,037ft

World’s next highest railway bridge in Indian Kashmir

MH370: Is plane deeper than inverted Burj Khalifa?