The exterior railings of the 125 year-old Schatzalp Hotel in Davos were in poor condition. Researchers at ETH Zurich teamed up with a local timber construction company and an ETH spin-off to find a replacement, using state-of-the-art technology.
In brief
- Wooden balustrades of covered balconies at Schatzalp Alpine hotel rotten and too low for modern standards.
- Researchers in architecture at ETH Zurich use digital processes to design new railing elements that are easy to assemble and repair.
- Individual parts manufactured by Davos-based timber construction company using augmented reality technology. Final piece of balustrade recently installed on façade of Alpine hotel.
The covered balconies of the art nouveau building at Schatzalp have seen a lot over the years. Where once wealthy patients convalesced from tuberculosis in the fresh air, today hotel guests enjoy sunbathing or taking in the view of the Davos mountains. Many of the wooden railings on the loggias - as the side-enclosed, covered balconies are known - are as old as the former sanatorium itself: 125 years old, to be precise. All those years of snow, wind, rain and sun have left their mark on the wood.
"The balustrades were in poor condition, especially on the first floor, where they stick out and are particularly exposed to the elements," says Silke Langenberg, Professor of Construction Heritage and Preservation at ETH Zurich. On top of that, the height of the railings didn't meet current safety requirements.
Façade altered multiple times
Together with ETH architecture professors Fabio Gramazio and Matthias Kohler, Langenberg went looking for solutions for a suitable replacement. A building survey revealed that the railings were not uniformly constructed because they had been built at different times and used different connections and joints. "The typical image of the Schatzalp as we know it today, with its loggias running along the entire southern façade, didn't come about until the late 1940s," says Langenberg. "When you stand in front of the building, you can still see the many changes that have been made to the façade over the years." That, combined with the damage and the need to increase the height, was the reason for designing the new railings.
A reconstruction of the original balustrades was quickly rejected, says the professor. This would go against the principles of monument preservation. Plus, the design of the old railings was based on a square grid. "That design would have had to change given the necessary increase to the height, otherwise the only solution would have been an additional, higher handrail. Since all the railings had to be replaced, however, we worked together to find a design that would work despite the increase in height, that would meet the safety requirements and needs of the hotel, and which would still blend harmoniously with the existing structure."
"We reinterpreted the balustrades based on the design logic of the older examples," adds Fabio Gramazio. For the Gramazio Kohler Research professor of architecture, who primarily works with digital design technologies, working on a listed building was a new experience - and an exciting one.
Countless versions tested
How can the balustrades be renovated while keeping the unique and attractive visual character of this historic building? And how can digital technologies be integrated into existing craftsmanship and operational processes? These were the questions the researchers asked themselves.
As is standard practice in digital design, they developed a parametric model. This type of design constantly adapts to different dimensions or contours. "We tested various versions virtually and discussed them repeatedly with everyone involved," says Matthias Kohler. "That's how we finally decided what the new railing should look like and how it could be manufactured as simply as possible."
Augmented reality in the Alps
It was important to those involved in the project that a local company manufacture the wooden balustrades. The carpenters at timber construction company Künzli Davos AG were supported in this effort by ETH spin-off Incon.ai. With its augmented reality technology, they were able to manufacture the individual elements more easily: a projector hung from the ceiling of the workshop in Davos, projecting the 3D model of the individual railing elements onto the work surface below. This showed the carpenters where each part would go and how to assemble them.
"It's a fundamental shift in the way we build," says Kohler. "Visual technologies are essentially replacing the tape measure. In traditional design, you're constantly switching back and forth between the plan hanging on the wall and the workpiece, measuring and checking. With augmented reality, the design is displayed on the table in front of you in three dimensions."
This approach also has a significant impact on the design, explains Kohler. "It raises different questions. What data do you need to see when, and how, in order to build using digital tools? What can people contribute and what information is needed in the plan?"
During execution, humans and technology support each other, as Kohler points out. The digital model shows what goes where and how. Humans, on the other hand, bring dexterity and intuition to the process. "Digital technology does not dominate humans. On the contrary, humans are in control of the entire process."
Subtle design
At first glance, the new balustrades look identical, but there are tiny differences that only become apparent on closer inspection. The new balustrades play with the fact that individual wooden slats open up a bit more in some places and are woven together more tightly in others. This creates an appealing pattern.
