Construction prototype for ultra-thin concrete roof: HiLo roof passes field test

Under the lead of NCCR Director Philippe Block's professorship, researchers from ETH Zurich have built a prototype of an ultra-thin, curved concrete roof using innovative digital design and fabrication methods. Several researchers of the NCCR Digital Fabrication actively contributed to this flagship project. The tested novel formwork system will be used in an actual construction project for the first time next year.

The shell is part of a roof-top apartment unit called HiLo that is planned to be built next year on the NEST, the living lab building of Empa and Eawag in Dübendorf. The penthouse will provide living and work space for guest faculty of Empa. Researchers led by Philippe Block, NCCR Director and ETH Professor of Architecture and Structures, and Arno Schlüter, ETH Professor of Architecture and Building Systems, want to put the new lightweight construction to the test and combine it with intelligent and adaptive building systems.

Tried and tested to scale

The building technique for the roof was developed by the Block Research Group, led by NCCR Director Philippe Block and senior researcher Dr. Tom Van Mele, together with the architecture office supermanoeuvre, and tested out on a full-scale prototype. The prototype was 7.5 m high with a surface area of 160 m2 (covering an area in plan of 120 m2). The thickness of the concrete has an average thickness of 5 cm varying between 3 cm along the edges of the roof to 12 cm at the support surfaces. Instead of formwork using non-reusable custom-fabricated timber or milled foam, which would be needed to realise such sophisticated form, the researchers used a net of steel cables stretched into a reusable scaffolding structure. This cable net supported a polymer textile that together functioned as the formwork for the concrete.

Algorithms for controlling the shape

The cable net is designed to take on the desired shape under the weight of the wet concrete, thanks to a calculation method developed by the Block Researcher Group and their collaborators in the Swiss National Centre of Competence (NCCR) in Digital Fabrication. The algorithms ensure that the forces are distributed correctly between the individual steel cables and the roof assumes the intended shape precisely. The cable net weighs just 500 kg and the textile 300 kg; thus, with a total of only 800 kg of material the 20 tons of wet concrete are supported. The construction of the roof would be inconceivable without state-of-the-art computation and fabrication techniques.

More information in ETH Zurich's media release and on the project website

Detailed information about the building process, quotes as well as image and video material can be found in the extended media release by ETH Zurich. Further information is available on the project website of the Block Research Group.

Credits NEST HiLo roof prototype

Design and Engineering

Block Research Group, ETH ZUrich



Mathematical and Physical Geodesy, ETH Zurich

Automatic Control Laboratory, ETH Zurich


Marti [general contractor]

Bürgin Creations [concrete works]

Holcim Schweiz [concrete development]

Doka [scaffolding]


Jakob [cables]

Bruno Lehmann [rods + cable-net components]

Blumer Lehmann [timber]

Dafotech [steel supports + plates]

Bieri [fabric cutting + sewing]


ETH Zurich

NCCR Digital Fabrication

Holcim Schweiz



Text adapted from ETH News.

Image credits: Block Research Group, Michael Lyrenmann 2017

Hi Lo 002 DSC 0043 Michael Lyrenmann 1024x684