An Ultra-Thin Double-Curved Concrete Roof

A group of researchers from ETH Zurich have designed and built a 25-foot-tall prototype for an ultra-thin, lightweight, and double-curved, concrete roof, that is set to be used in a residential construction project next year. With an average thickness of nearly 2″, the structure varies between 1.2″-thick on the edges to 4.7″-thick at the roof’s support areas.

The roof’s self-supporting, double-curved shell is comprised of several layers, including heating and cooling coils, and insulation that are sandwiched between two concrete layers. The exterior layer is covered with thin-film photovoltaic cells that will generate energy for the designated building.

A new construction technique for the structure was developed by the Block Research Group of the ETH Zurich’s Institute of Technology in Architecture, led by associate professor Philippe Block, senior researcher Tom Van Mele, and international architecture firm Supermanoeuvre. The technique substitutes “a net of steel cables, stretched into a reusable scaffolding structure,” for the temporary formwork, noted the release. “This cable net supported a polymer textile that together functioned as the formwork for the concrete.” With the help of computer algorithms, the team successfully designed the cable net to reach the intended shape under the weight of wet concrete. “The cable net weighs just [1,100 pounds] and the textile [weighs 660 pounds]; thus, with a total of only 1,770 pounds of material, the 20 tons (40,000 pounds) of wet concrete are supported.”

Built over the course of six months, the entire research and development process took nearly four years. “We’ve shown that it’s possible to build an exciting thin concrete shell structure using a lightweight, flexible formwork,” said Block in the same release. “Thus demonstrating that complex concrete structures can be formed without wasting large amounts of material for their construction.”