News Treehugger Voices Broad Sustainable Building Completes World's Tallest Prefab, 57 Stories By Lloyd Alter Lloyd Alter Facebook Twitter Design Editor University of Toronto Lloyd Alter is Design Editor for Treehugger and teaches Sustainable Design at Ryerson University in Toronto. Learn about our editorial process Updated October 11, 2018 Share Twitter Pinterest Email Screen capture. Broad Sustainable Building News Environment Business & Policy Science Animals Home & Design Current Events Treehugger Voices News Archive This TreeHugger is a huge fan of Broad Sustainable Building's prefab building technology, and I have been impressed by the passion of its chairman Zhang Yue, who is trying to build the world's tallest building, Sky City. He now has built a big slice of it next to his factory in Changsha, as offices and housing for families of employees at Broad. This building, which rose at the rate of three floors per day, has 57 floors and 800 apartments. Chairman Zhang's problems in building Sky City have been political rather than technical; even this project got halted at 20 floors while the government decided how tall it could be. It was supposed to be 97 floors but got chopped to 57, ostensibly because of a neighboring airport. However that is still the world's tallest flatpack prefab. Broad Sustainable Building/Screen capture A key element in the design of Sky City is the interior square and "sky street" that connects the building vertically. There are 19 of these 3 story high atria stacked on top of each other, and 3.6 km (2.23 miles) of ramp. The atria can be used for basketball, tennis, theaters or even vertical farms. Broad Sustainable Building/Screen capture When I visited the site in the spring, I had some doubts about whether these would ever get used when there are banks of elevators; these are steep compared to the ramps that get built in North America. I was surprised and pleased to see in the video that there were bikes and golf carts running up and down the ramps, that they are really working as streets. Perhaps like those people in Italian hill towns, they will outlive us all thanks to all that climbing; certainly the air quality in Broad's buildings is far better than it is outside, even in suburban Changsha. Broad Sustainable Building/Screen capture As usual for Broad's buildings, they are really efficient, with 8" of insulation and quadruple-glazed windows and the best air quality in China, with 3 stage air purification, particulates reduced by 99.9%, 7 air changes per hour and 100% fresh air that's run through heat recovery ventilators. It's got combined heating, cooling and power, (Broad's main business is air conditioning) making the building 80% more efficient than conventional buildings. Broad claims that this one building saved 15,000 trucks full of concrete. Lloyd Alter/CC BY 2.0 There is not a lot of enthusiasm for BSB towers in China, probably because it is too fast, too efficient. It seems that half the country is employed in building residential buildings the traditional way (as in photo of Changsha construction above) and the other half of the country is speculating in them. This is a real shame, because there is simply no comparison in construction quality, and you certainly don't want to breathe the air out there on a smoggy day. Lloyd Alter/CC BY 2.0 Broad Sustainable Building does not build on site out of concrete; it prefabricates the steel frame components and floor panels in a small town a 90 minute drive away from Changsha, although it may take less time now that a six-lane divided highway has been built. Lloyd Alter/CC BY 2.0 Inside the vast and spotless factory buildings, the floor panels are assembled, complete with drywall, plumbing, electrical, ventilation and floor coverings. Lloyd Alter/CC BY 2.0 Note the legs that are separating the two floor assemblies; there are sockets welded into the top and bottom to permit attachment of these spacers, which also serve as lifting points. This protects the finishes, but also lets Broad pile all the wall components, bathroom fixtures and even furniture that get lifted together with the very floor panel that they will be sitting on in the finished building. Lloyd Alter/CC BY 2.0 Whenever I have written about Broad before, and their incredible speed, there have been comments about how it can't possibly be safe to build so quickly, that they must be cutting corners. I think the opposite is true; Here, workers are bolting together some of the large frame pieces that form the structure of the building. Note the special cage that has been dropped over the beam so that they can assemble it in comfortable working conditions. In North America you would probably see some guy on a ladder. Here, they can work so fast because they have actually thought out the actual process of assembly and built the jigs and the tools to do it fast, efficiently and safely. If I sound impressed, it is because it is like nothing I have seen anywhere, and I have toured a lot of prefab housing factories. Broad Sustainable Building/Screen capture I still have lots of issues with the design of these buildings, particularly with the placement of the atria in the middle of the building where they don't get much natural light, and with the ramps that I thought were too steep. There is too little attention to architectural detail, although the new aluminum cladding adds variety; this is an engineering project, not an architectural one. I just wish Broad would hire architects like Ma Yansong and Dang Qun of MAD; they could do wonders with this. But designs can be fixed and these problems are minor compared to the scale of accomplishment here; Broad Sustainable Buildings is producing tall, healthy and efficient buildings at a quality and speed that has not been done anywhere else. They should be building a whole lot more of them.