Allmend School, located in south-western Zürich’s densely populated Manegg district and Switzerland’s first certified 2000 Watt ‘Greencity’, is designed to promote sustainable living and help minimize the environmental footprint of the area’s inhabitants. Constructed to Minergie-P ECO standards, the three-story, earthquake-resistant new build is the product of an architectural design competition. The brief called for the creation of as much public space as possible on the constrained site in order to deliver added value for the surrounding neighborhood. The result is a school with a striking, stand-out feature: an all-weather, roof-top sports pitch. 16m above the ground and open to all, it is accessed by an external spiral staircase.

Constructed on shallow foundations, the new build is essentially a designed-for-disassembly (DfD) skeleton timber structure. Both the building’s base and its solid access cores, which also provide structural reinforcement, are made of cast-in-situ recycled reinforced concrete.

In contrast, the canopy that covers the all-weather pitch and doubles up as the substructure for the 1300 m², 172 kWp array of 534 PV modules is a simple steel structure of classic construction. Reminiscent of an unclad sports hall building, it was designed and dimensioned to standard structural requirements.

Part and parcel of the design right from the initial competition entry, the canopy was conceived to offer unity of design coupled with a fall-protection and ball-stop system. It ensures that the roof and PV array substructure are as light, elegant and open as possible, while also providing the necessary height. Steel proved the perfect construction material. Thanks to its high load-bearing capacity and design flexibility, the steel framework permits large span widths without intrusive columns. A robust and durable material that guarantees excellent resistance to the elements, steel is also ideally suited to outdoor use.

The final result is a three-dimensional framework with single- rather than duplex-coated wind-bracing struts arranged for maximum performance. It is elegant, structurally slim and reduces material use and is therefore greener. Its clean, simple lines, exemplified by the bracing struts, are particularly impressive. It would have been possible to use heavier profiles and omit the diagonals had that been the objective. However, this would have produced a frame-based load-bearing system in which the frames were subject to greater shear forces and so required heavier profiles and chunkier joints. It would, in turn, have compromised the elegant appearance of the superstructure. The aim was to achieve a simplicity in keeping with the rest of the build and a design that ‘made sense’ and matched the overarching idea.

The Haspelsteg Footbridge with its slim steel bridge girders is a key element in the new Allmend School development. Crossing Allmendstrasse, the SZU railway lines and Maneggstrasse, it offers a safe connection between the two halves of the former industrial zone. The bridge was constructed according to the principles of economy, functionality and durability in a design process that considered fitness for purpose (subsidence, deformation, vibrations, etc.), maintainability and repairability (accessibility).

Measuring some 74 meters in length, the load-bearing structure is accessed via stairs and lifts at its eastern and western ends and in Locher-Oeri-Platz. The maximum free span width between supports is 33.1 meters. Once delivered to site, the prefabricated bridge girders were lifted into place on their abutments by a mobile crane, enabling trains to continue running as usual on the tracks below throughout construction.