SKY CITY is an 838m (2,749ft) tall skyscraper approved for construction 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,but this is not counting 120 days of prefabrication before on-site work commences; the total schedule is 210 days. If completed, it could become the tallest building in the world.
Broad Sustainable Building, who specialise in making buildings that are sustainable, cost less, use environment friendly materials and can be built in a short amount of time, using techniques like prefabrication, had intended to build a 666m (2,185ft) tall skyscraper, but the local government wanted the world's tallest building, hence the current plans. The company has constructed 20 buildings in China using the same method and has several franchise partners globally.
If built as planned and to schedule, Sky City would likely be the tallest building in the world, with 220 floors and a total height of 838m (2,749ft). 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 build site. The fabrication process is due to take around six months, before the actual construction begins.
According to the plan, the building, across 220 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. 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 everybody in a given floor within 15 minutes; the building will be fire-resistant for up to three hours. It will also have 17 helipads.
For transportation there will be 104 high-speed elevators installed. Many have critiqued the safety of these potential elevators, because they take multiple 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(1,400,000sqft) and a 3 to 7 floor-high annex of 35,000m2(380,000sqft). The total capacity of the building will be about 30,000.
The 4-layered glass used for the building's windows will keep the temperature of the building constant between 20 to 27 °C (68to 81°F). The air indoors will be specially filtered to be up to 20 times cleaner than the air outside. The lamps used in the building will be made of LEDs, saving energy. It has also been claimed by the builders that they are currently working with architects who worked on the Burj Khalifa.
The project will 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 reflected in 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 6inches (15cm) of insulated walls and quadruple glazing, contributing greatly to energy efficiency. The building will be designed to be resistant to earthquakes of up to 9.0 on the Richter 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.
A cost estimate of $1500 per square meter of floor space would make Sky City considerably cheaper than the similarly tall Burj Khalifa($4500 per square meter). The total cost is also considerably less, with the Burj requiring about £940 million ($1500 million) in 5 years, compared to Sky City's £400 million ($625 million) in 90 days. Broad Sustainable Group has purchased 67,300m2(724,000sqft) of land, for a cost of 390 million yuan ($63 million).
The project has been delayed in its schedule several times in the past, particularly due to awaiting government approval on starting construction. In October 2012, the group announced that they had received approval from the local government and that construction would begin in November, but announced a new build time of 210 days. This meant completion of the project in June 2013.
On June 17, 2013, Broad Sustainable Building Group Chairman Zhang Yue said that construction will commence in August 2013 with the first four months spent for prefabrication and the next three months for installation onsite. The expected date of completion is March 2014.