Architect: baubüro in situ

Image: Martin Zeller

Circular Design

K118 Project in Zurich

Climate-friendly construction is already possible by the reuse of construction materials. A recent example of this is shown by the K118 project in Winterthur. An existing factory building has been extended by the addition of three additional floors, providing studio and workshop space. It has been estimated that a saving of 59% of greenhouse gas emissions has been made and 494t of primary material saved in comparison with using new materials.

Designed by baubüro, one of the pioneers of sustainable construction in Germany, K118 has been used as a pilot project on the practicality of material reuse. The pilot project quickly showed that circular building involved thinking in a totally different way to normal design and planning cycles.

When starting from available building components, the planning process is turned on its head. Opportunities need to be taken as they arise that will then impact the design, which starts with the sourcing of materials. Selection is followed by cataloguing and checking of material integrity. In this way, the design is created along with the planning phases in a constant process of evaluating, checking, and readaptation.

K118 has a large and varied range of reused components. Windows, natural stone slabs, wooden roof elements, EPS insulation, aluminium profile sheets and of course steel. A steel frame that once supported a distribution centre on the Lysbüchel site in Basel forms the supporting structure to the three-storey extension. Steel lends itself particularly well to reuse especially if bolted connections have been used and is hot dip galvanized.

K118 Project ZurichBolted connections simplify non-destructive disassembly and reassembly, and hot dip galvanizing protects steel from corrosion increasing its reuse cycles. This creates the prerequisite for renewed use without additional repair measures and is exemplified by K118.

A 28-year-old galvanized steel escape staircase has been demounted and reused within the project. The 22 m high structure was originally built in 1990 for the Zurich Orion office building

It now provides access to the new extension. No maintenance was needed for the galvanized steelwork, only minor modifications were necessary in order for it to fit the new dimensions for its new use.

One example being larger treads, to meet today’s fall protection requirements. The seven-storey staircase is also a good example of the reversal of the planning process, as its landings determined the storey heights of the extension.

K118 Project Zurich

By reusing materials, the CO2 emissions of K118 compared to a new construction were reduced by 59% or 494 t. The reused steel contributed to a CO2 reduction of 16% or approximately 80 t.

While the CO2 emissions could be reduced as described, the total construction cost was comparable to that for a new building. The majority of the costs were for the work required to refashion the reused materials. K118 has been awarded a Gold Global Holcim Award.


Architect: baubüro in situ

Image: Martin Zeller

Posted on July 21, 2022 by Galvanizers Association

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