Rendering Courtesy of Broad Group
At 838 meters, Sky City would be the world's tallest building.
Photo Copyright tobyphillipsphotography
Broad Group Chairman Zhang Yue (right) gave a presentation on Sky City at the 2013 London conference of the Council on Tall Buildings and Urban Habitat.
Video by Council on Tall Buildings and Urban Habitat
Full video of Zhang Yue's presentation to CTBUH's London conference in June 2013.

On July 20, a groundbreaking ceremony was held in Changsha, China, for Sky City, an 838-meter-tall, 202-floor mixed-use tower that, if completed, would be the tallest building in the world. The $1.47-billion project is the brainchild of Changsha-based Broad Group, which plans to use its own modular fabrication and construction techniques to erect the supertall building in only seven months. The ambitious plan has drawn worldwide attention as well as the ire of Chinese government authorities, who say the Broad Group lacks the proper permits to begin construction.

Plans for Sky City are ambitious, even for a supertall building that aims to outdo the Burj Khalifa's height by 10 m. With 1.05 million sq m of build area, Broad Group hopes the tower will someday serve as a self-contained city: a home for more than 30,000 residents who will live and work entirely within the building.

The aggressive construction schedule calls for seven months of work once the foundation is built. This work would include four months of modular-component fabrication by 20,000 Broad Group workers in the nearby Broad Group factories and three months of on-site installation by a team of 3,000 workers.

Broad Group's main business is manufacturing air-conditioning and related HVAC systems. But their Broad Sustainable Building division has been turning heads in recent years with high-profile demonstration projects such as the modular T30 Hotel, a 30-story building that was erected in about 15 days. A time-lapse video of the construction drew millions of views on YouTube.

On June 12, Zhang Yue, chairman of Broad Group, spoke to the London conference of the Council on Tall Buildings and Urban Habitat (see video). "You have seen our 30-story building built in two weeks, and that applies to [Sky City] as well," he said, through a translator. "People have seen our video on YouTube, and this kind of building we're building almost every day right now."

During his presentation, Zhang repeatedly emphasized the importance of energy use and conservation in the design of Sky City. "This building, as compared to a conventional buildings in the local area, can decrease energy consumption by 50%. We are building this 202-story building, [and] our main hope is to draw people's attention to see that, within a building, there is such a big area for energy-consumption [savings]."

Zhang and the Broad Group have been promoting Sky City for some time, but the design community is skeptical. "It seems impossible what they're trying to do. But Zhang Yue is very serious, and has not wavered from what he is going to do," said Antony Wood, executive director of the Council on Tall Buildings and Urban Habitat (CTBUH). "We at the council see almost every week a world's-tallest-building proposal. Most never get past the Frank Lloyd Wright Mile-High Building' render stage."

Wood and several members of the council visited the Broad Group manufacturing facility in Changsha in late 2012 and toured Broad Group's modular-fabrication factories. "I went there with great skepticism and came away massively impressed with what they were doing as evidenced by their whole process of prototyping buildings," Wood told ENR. "I am still not 100% convinced of the leap from 30 to 200 stories with the prefabrication system, but am I massively more convinced than before I went there."

But Wood did take issue with the proposal's emphasis on speed. "The No. 1 criteria for this project is: if it is achievable, to build the world's tallest building, prefabricated," he said. "I don't care if it takes four times as long, four years or eight years—is it achievable to build a prefabricated supertall building safely and occupy it?"

Broad Group's Zhang claims Sky City could handle a magnitude-9 earthquake, but Wood says the company needs to be more open about how it will meet this goal from an engineering standpoint. "There is the issue of technical feasibility. The concern raised most is structural stability, especially in an earthquake zone."