The Cadenza Stair at STEP2

The preassembled helical stair being hoisted by the crane to the STEP2 Unit, on the third floor of the NEST Building. Photo: Georgia Chousou

Cadenza, the helical concrete stair of the STEP2 Unit has just been installed at NEST in Dübendorf for Empa and Eawag. Our research shows how cutting-edge engineering and fabrication technology enable bespoke designs with radically new aesthetics that efficiently use high-performance materials. The design, engineering, and digital fabrication of the stair were a collaborative endeavour of experts from Digital Building Technologies ETH Zürich, ROK Architects, SW Umwelttechnik, the BASF subsidiary Forward AM, New Digital Craft, WaltGalmarini AG, and the Empa spin-off re-fer.

The stair demonstrates a structurally optimised use of material, with steps less than 20 mm thick and weighing only 45 kg. The efficiency is further enhanced by the concentration of reinforcement in three memory®-steel post-tensioning bars located in the load-bearing stringer. The complex geometry of the 16 concrete steps was achieved using a single set of reusable 3D-printed formworks. The steps and the two-part landing were designed to be assembled with dry connections only, making the tectonic concept compatible with refurbishments and circular economy architecture, being modular, and ready to be dismantled and reassembled.

The preassembled Cadenza stair in the Empa Bauhalle. Photo: Han Seul Ju
The preassembled stair was stabilised for transport by a temporary steel and timber core. Photo: Andrei Jipa
The Cadenza stair in its final position in the STEP2 NEST Unit. Photo: Georgia Chousou

Stair design: Digital Building Technologies – ETH Zurich, ROK Architects
Fabrication system: Digital Building Technologies – ETH Zurich, SW Umwelttechnik
Formwork development and 3D printing: Digital Building Technologies – ETH Zurich, BASF Forward AMNew Digital Craft
Structural design: WaltGalmarini AG
Precast concrete: SW Umwelttechnik
Post-tensioning systemre-fer
Project management: ROK Architects