Sky City (Chinese: 天空城市; pinyin: tiānkōng chéngshì), or Sky City One, was an 838-metre-tall (2,749 ft) planned skyscraper in the city of Changsha, Hunan in south-central China. The prospective builders, Broad Sustainable Building, estimated it would take just 90 days to construct. Including the 120 days needed for prefabrication before on-site work commenced, the total time needed was 210 days. Pre-construction activities were halted in August 2013 after government regulators required additional approvals. Broad Sustainable Building had intended to build a 666-metre (2,185 ft) skyscraper, but the local government wanted the world's tallest building; hence the revised plans. The company has constructed 20 buildings in China using the same method and has several franchise partners globally. It was planned to include a helipad at a height of 739.8 m (2,427 ft) above ground. As of May 2016, plans for the building's construction were stalled, and the foundations of the planned building were being used as a fish farm. On 8 June 2016, it was reported by the People's Daily that the project had been dropped due to protests over environmental damage to the Daze Lake wetland. The People's Daily said, "Central China's Hunan province finally announced a halt on its ambitious plan to build the world's tallest tower within one part of its rare wetland area. The Daze Lake wetland is the location where the world's next tallest tower was originally scheduled to be built. This wetland is now listed as one of the 20 waters to be permanently protected and will follow non-construction zone policies. It is a pristine wetland hailed as the last wetland in Changsha where many rare bird species take habitat. Shelter of these birds would be largely disrupted by the building of this tower." However Broad Group declared: "We will definitely build the tower" in 2016.
Building layout Had it been built, Sky City would have been the tallest building in the world, until the Jeddah Tower in Jeddah is complete, with 202 floors. The construction plan calls for it to be built from pre-fabricated units constructed on site in an unprecedentedly short period of 90 days. BSB's plan is to assemble 95% of the building in its factory before any excavation takes place at the construction site. The fabrication process is due to take around six months before the actual construction begins. According to the plan, the building's 202 stories will have a hotel accommodating 1000 guests, a hospital, 5 schools, and offices. Of the total space available, nearly 83% will be for residential purposes, housing up to 17,000 people. Another 5% will be for the hotel housing 1000, while 3% each will be dedicated to schools, hospitals, offices and shops. There will be 10 fire escape routes, which will evacuate a given floor within 15 minutes; the building will be fire-resistant for up to three hours. It will also have 17 helipads. Sport facilities will include six basketball courts and 10 tennis courts. Plans include preserving some green space around the building. For transportation there will be 104 high-speed elevators installed. The safety of these potential elevators has been questioned because they take several minutes to get from bottom to top. The 5000 residential properties will be able to accommodate 17,400 residents. The proposed building will have total floor space of 1.2 million m2 (13 million sq ft). The main building will have 1.05 million m2 (11 million sq ft) of this area, with a basement of 130,000 m2 (1,400,000 sq ft) and a 3 to 7 floor-high annex of 35,000 m2 (380,000 sq ft). The total capacity of the building will be about 30,000. The four-layered glass used for the building's windows will keep the temperature of the building constant between 20 and 27 °C (68 and 81 °F). The air indoors will be filtered to be up to 20 times cleaner than the air outside. The lamps used in the building will be made of LEDs. The builders have claimed to be working with some of the same architects who designed the Burj Khalifa, such as Adrian Smith.
Structural features The project is planned to consume 270,000 tons of steel. For its assembly factory, sustainable building technology and independent research and development will be required. The main advantages of the building will be its earthquake resistance, energy saving, cleanliness, durability, and materials, which consist of recycled building materials, non-aldehyde / non-lead / non-asbestos building materials, etc. The technology at the core of the whole steel structure is modular construction. The building would have 6 inches (15 cm) of insulated walls and quadruple glazing, contributing greatly to energy efficiency. The building will be designed to resist earthquakes of up to 9.0 on the Richter magnitude scale. Although structural details are not available, outside architects have expressed doubts that a modular design would have the stiffness on lower floors to withstand the wind loads imposed by such a height, without unacceptable amounts of sway, or that the building could be built without high-strength concrete, whose curing time would preclude such a rapid construction rate. Most of the construction and production of materials will take place on site so as to benefit the local economy of Changsha.
Cost As currently planned, Sky City would cost RMB 9 billion ($1.46 billion) to build. A cost estimate of $1,500 per square meter of floor space would make Sky City considerably cheaper than the similarly tall Burj Khalifa ($4,500 per square meter). Broad Sustainable Group has purchased 67,300 m2 (724,000 sq ft) of land, for a cost of 390 million yuan ($63 million).
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