More basic hurdles appeared during the Q&A for the CTBUH conference talk. The prefabricated modules for Sky City are all made of steel, and Broad Group's Zhang admitted his company's steel fabrication capabilities are limited. Broad Group has released little information about the design and engineering of Sky City's foundation. According to the company's press materials, the seven-month schedule does not include construction of a foundation or site preparation, work that has taken a year or more on other recent supertall building projects.
While a supertall tower built entirely from prefabricated modules is a novelty, prefab elements are nothing new. "Modular construction has always been an important part of modern architecture," says Bill Baker, partner with Skidmore, Owings & Merrill and the structural engineer for the Burj Khalifa. "Steel comes prefabricated, concrete buildings are partially prefabricated ... the question is, does it come with the rest of the building?"
Baker declined to comment directly on the Sky City project but says he sees an uptick in interest in large-scale modular construction, some of it driven by high-profile projects such as the B2 building in Brooklyn, N.Y. "It will be interesting to see how all this develops, how much can come together to minimize the fieldwork. I wouldn't call it the Holy Grail, but [totally modular construction] is certainly something people strive for," he says.
Engineering challenges aside, Sky City's dream already may be in jeopardy. A few days after groundbreaking, ">Chinese media reported that work had been halted because of missing permits. In his June presentation to the CTBUH conference, Zhang said, "In the past 12 months, we have been undergoing the review process by the government." However, he did not specifically mention having acquired the permits. At press time, Broad Group had declined to respond to ENR's queries.