In this era of megatall skyscraper construction around the world, Jeddah Tower is the first that aims to exceed the previously undreamed-of one-kilometer threshold.

When it is completed in 2020, the 1,000-meter tower in Jeddah, Saudi Arabia, designed by architect Adrian Smith, will become the world’s tallest building, easily eclipsing Burj Khalifa, the 830-meter-tall Dubai skyscraper, also designed by Smith.

Jeddah Tower, previously known as Kingdom Tower, will be the signature tower that welcomes pilgrims to Jeddah, the gateway to Mecca and Medina. It will also be the mixed-use centerpiece and first phase of Jeddah Economic City.

At 300,000 square meters, Jeddah Tower will house office space on the bottom, topped by an opulent hotel, serviced apartments, and luxury condominiums. A circular observation deck, the tallest in the world, will protrude from one of the top levels. The building will have 56 elevators, and the top third of the three-legged concrete structure will be a hollow spire. Each of the tower’s three tapering sides will feature a series of notches that create shadow, serving as shields from the sun and providing outdoor terraces with stunning views.

Along with Smith, who is the founder of Chicago-based Adrian Smith + Gordon Gill Architecture, the other key player in the design and implementation of this momentous construction project has been principal engineer Robert Sinn.

Sinn, who is based in the Chicago office of structural engineering firm Thornton Tomasetti, came on board in 2009 to work with Smith on the design competition they later won.

“We had to make several adjustments as we went along,” Sinn says. “Fortunately, Adrian is the most experienced designer of supertall buildings.”

“From the bottom of the foundation all the way up to the top of the tower, everything was a challenge,” Sinn says.

The taller the building, the more wind is an issue, Sinn explains. “Wind drives a lot of decisions on tall buildings. The taller they get, the wind-induced forces go up dramatically.”

“On average, we will see 75-miles-per-hour gusts monthly at the top of the tower, with 90-miles-per-hour gusts on average at least once on an annual basis,” he says.

The best way to counteract gravity—and keep the supertall structure upright—is to use the weight of the building itself to counteract the effects of high wind loads. And that called for lots of heavy concrete in the design and implied construction of the tower.

Using steel instead of concrete would have been impractical, Sinn says. “Generally speaking, steel wouldn’t have weighed enough to sustain the extreme height of the building.” Concrete weighs far more than steel, and it helps to fight the overturning effect of wind on the building’s foundation.

Concrete also helps to control the motion of the building—the swaying movement that people feel inside the tower on windy days, he explains.

Sinn promises that building motion on the topmost occupied floor, the 160th, will be fine. “Because of the shape of the building and the structure of the building, it will be very, very comfortable for the occupants up there—very, very calm.”