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Sky City: The Skyscraper China Tried (and Failed) to Build in 90 Days

The Empire State Building? At 443 meters tall, it took over a year to build. Burj Khalifa in Dubai, currently the world’s tallest building? At 828 meters tall, it took nearly six years to build. 

With Sky City, or tiānkōng chéngshì in Mandarin, Chinese construction company Broad Sustainable Building, a subsidiary of Broad Group, wanted to set a new record. Located in Changsha in China’s Hunan Province and measuring 838 meters tall, or 2,749 feet, the proposed skyscraper would not only have earned the title of world’s tallest, but they said they’d build it in just 90 days.

If that seems impossible, you wouldn’t be the first to say so. In fact, you’d be in agreement with a number of internationally renowned structural engineers and architects. Unfortunately, we may never know because as of 2016, construction of Sky City has been postponed indefinitely. Nevertheless, Broad Sustainable Building insists their plans are not only doable, but that they’ll go through with them sooner or later.


When most people think of prefabricated buildings, they imagine Oklahoma trailer parks filled with vinyl-sided single-family homes that inevitably get sucked up by a tornado. However, with Sky City, Broad Sustainable Building wanted to take the same principles and use them to construct a massive tower at the unprecedented speed of five floors per day.

The building would have been constructed using prefabricated modules assembled in factories beforehand, the main reason Broad Group claimed they could complete it in 90 days. Some 95% of Sky City would have been built this way allowing Broad Group to just snap the pieces together like a Lego set at the construction site. This prefabrication itself wasn’t included in the original time estimate and would have extended the total construction time to 210 days.

Because the modular prefabrication design favors steel over concrete, which has to be poured onsite and is therefore more time intensive, Broad Group estimated it would need 270,000 tons of steel to build Sky City. In comparison, the similarly tall Burj Khalifa used around 43,000 tons of steel.


Broad Sustainable Building named their tower “Sky City” for a reason. At 220 stories, the skyscraper would have had over a million square meters of floor space. That’s more than a square kilometer or around 250 acres, bigger than the entire area of the SoHo neighborhood in Manhattan.

Comparatively, the Burj Khalifa, which is just 30 meters shorter, has only 300,000 square meters, or over 3 million square feet, of floor space. That’s because Sky City wouldn’t just have been tall, but wide as well. Renderings suggest it would have been about twice as wide as Burj Khalifa at the midpoint.

The Burj Khalifa
The Burj Khalifa. By Nicolas Lannuzel, is licensed under CC-BY-SA

With that much space, Broad Group wanted Sky City to have basically all the amenities and services needed in a “city.” Someone could have theoretically lived in the building without ever having to leave. 

Specifically, 83% of the building would have been dedicated to residential purposes with housing for over 4,000 families. Another 1,000 people could have stayed in the building’s hotel, taking up 5% of the floor space. The apartments and hotel would have been located on the 16th to 180th floors.  

Additionally, the 1st to 5th floors would have contained schools, hospitals, daycare centers, supermarkets, shops and clinics while the 181st to 219th floors would have featured restaurants with views of Changsha City. Residents and visitors would also have had recreation options thanks to six basketball courts and 10 tennis courts. There would have been a number of helipads as well. Altogether, the building would have had capacity for 30,000.

Of course, a city is more than just houses and stores. You also need transportation. Broad Group planned for people to get around their vertical city via 104 high-speed elevators. It’s unclear exactly how fast these elevators would have gone since they were never manufactured, but if they’d been anything like elevators in similarly tall megastructures, they may have reached speeds of around 60 kilometers an hour, about 35 miles per hour. 

Presumably, someone could have gotten from the bottom to the top of the structure in just a few minutes. Considering many people commute for over an hour across their city to work via cars or public transportation, that seems fairly efficient.

Despite its massive size, Broad Group claimed they could build their prefabricated skyscraper for pennies on the dollar compared to other megastructures. The building was estimated at around 9 billion RMB, or 1.46 billion US dollars. 

That might sound like a lot, but keep in mind that Burj Khalifa, which is similar in height but has only about 30% the floor space, cost 1.5 billion dollars. In other words, while Burj Khalifa cost around $4,500 per square meter, Sky City would have only cost just $1,500 per square meter. 

Additionally, Broad Group bought the land for the project, about 67,000 square meters or over 16 acres, for 390 million RMB, or 63 million US dollars. While not a bad deal, this was still a major investment for the firm. The same amount of land in New York City would cost you on average 83 million dollars.   


As their name would suggest, Broad Sustainable Building wanted to design Sky City with modern features that would have made it energy efficient and habitable over the long term while decreasing the per-capita use of land. First and foremost, the design involved recycled materials in the construction process, none of which included aldehyde, lead, asbestos or other chemicals known to cause health or environmental problems.

Other important features were the 15 centimeters (6 inches) of insulation in the walls and the four-paned, glazed windows that would’ve helped keep the temperature inside the building between 20 and 27 degrees Celsius (68 to 81 degrees Fahrenheit). Plus, lighting in the building would have consisted of LEDs, and the elevators would have been designed to generate electricity when ascending unloaded or descending fully loaded. 

These features would have saved a lot of energy over the long run. In fact, it was claimed that Sky City would use 80% less energy than conventional buildings.

Additionally, the internal environment would have been clean and healthy, even more so than outside. Specifically, a central vacuum system would have filtered the air, removing 99.8% of PM 2.5. PM 2.5 is fine particulate matter under 2.5 microns in length that’s widely implicated in both acute and chronic respiratory problems.

However, despite the modern design and sustainable features, many critics questioned the safety and environmental friendliness of Sky City’s design. Perhaps most dramatically, Bart Leclercq, now a Head of Studio for the Brewer-Smith-Brewer Group, the architects behind a number of glamorous buildings in the United Arab Emirates and Saudi Arabia, said he’d retire if the project were completed on time. Some wondered if Sky City was ever a serious proposal at all and not just a publicity stunt for Broad Group and Changsha City.

But it wasn’t just the timeframe that came into doubt. Many engineers expressed concerns about the integrity of the structure itself. Specifically, due to the design’s focus on steel over concrete, the structure might have had a lack of stiffness. Winds could have caused the building to sway considerably, destabilizing it.

Plus, many wondered about Sky City’s ability to respond to emergencies. In addition to a theorized three hours of fire resistance, there would have been multiple fire-escape routes, and the helipads could have been used for evacuation. Still, some worried this wasn’t enough to get the tens of thousands of occupants out of the building in case of fire, nor would there have been adequate means for rescue and firefighting personnel to reach the soaring heights. 

Lastly, the elevators might not have been enough to handle individual emergencies. Even though they would have been high speed, the incredible height of the building would’ve meant someone having an urgent health problem at the top would have taken several minutes to reach the hospital or doctors at the bottom. This could have prevented them from getting treatment in time.


Broad Group announced they’d received local approval for Sky City in October of 2012. They then said they’d begin construction that November. Including prefabrication, the project would have taken 210 days, meaning Sky City would have been finished in June 2013. 

Obviously, that didn’t happen. Groundbreaking didn’t take place until July of 2013 with China State Construction Engineering selected as the main contractor. The completion date was stated as April 2014 with official opening that May or June, already a bit longer of a timeframe than was initially proposed.

However, shortly after the groundbreaking, construction was halted because the project hadn’t received proper government approval. Despite approval from Changsha City, the height of the building meant it had to get the green light from national officials in Beijing, which apparently hadn’t happened.

For several years, Broad Group claimed it was moving through the red tape of government approval and would be starting construction shortly, but observers noted that they still weren’t even manufacturing building modules offsite yet. By 2015, the foundation pits that had been dug during the groundbreaking were filled with water and being used by local villagers for fish farming.

In 2016, the Sky City project received what many perceived as its final death blow. The original building site was located in Hunan province’s Daze Lake wetland, the last wetland in Changsha and home to some 135 species of bird. 

One of these birds is the Siberian White Crane which migrates south from Russia to spend the winter in southern China. The Siberian Crane is critically endangered with fewer than 4,000 individuals left in the wild. 

Environmental activists believed Sky City would disrupt the crane’s migration and nesting, further harming the population, as well as that of other protected birds like swans, amur falcons and cuckoo-doves. After protests and petitions to the government, a no-construction zone spanning 200 square kilometers, or 125 square miles, was declared in the wetlands right where Sky City was supposed to go. 


While the media and most skyscraper fanatics seem to consider Sky City a dead and forgotten ambition, Broad Group hasn’t given up so easily. Even in the face of the many setbacks, the company stated in 2016: “We will definitely build the tower.” Images of the proposed building can still be found on their website and YouTube channel, and renderings produced in 2017 suggest they’ve been looking for a new site, perhaps one closer to the waterfront. 

Chengsha may yet have its Sky City, but if it ever wants to hold the record for world’s tallest building, it will have to hurry. Jeddah Tower in Jeddah, Saudi Arabia, is already under construction. At exactly 1,000 meters tall, or 3,281 feet, Jeddah Tower would be the world’s first kilometer-tall building. As of 2019, the tower was about a third of the way done, but work has stalled due to labor problems. If Sky City can live up to its 90-day claims, it might just be able to make it in time.


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