Heavy snow means stress for roofs
Andermatt is now blanketed in snow, as it is every winter – and even more snow is on the way. This thrills the hearts of skiers and winter fans, but it also means substantial weight on roofs in the high-alpine destination. “The roof of The Chedi Andermatt must carry up to 1.5 tonnes of snow per square metre”, tells timber-structure engineer Andreas Burgherr from Timbatec. “As chance would have it, the roof structure was subjected to enough snow the very first winter to serve as a field test.” So the next predicted snowfalls are no cause for concern.
The structural design of a large roof like that of The Chedi Andermatt hotel – especially in the Alps where heavy snow loads must be expected – is a challenge. “The trick with The Chedi was to design an attractive roof with high load-bearing capacity but without being too thick”, explains Burgherr. In Andermatt one must expect snow loads up to 2.5 metres deep. This is shown on the Swiss Snow Map, and is based on the altitude and the general climatic characteristics of Andermatt. That’s why the engineers decided to use a style of trussed roof structure known as the liegenden stuhl . Thomas Balzli, project manager at Andermatt Swiss Alps AG, explains this technical solution as follows: “The trusses have arched timber braces that support the roof and can flex to withstand high snow loads.” Burgherr adds: “The dormer windows were a critical point. These had to be completely isolated against the effects of snow loads, otherwise the windows would break. That’s why we provided space for movement around every window in the roof, which allows for the bending of the rafters.
Not only is the roof structure designed to carry snow loads; the roof itself is also specially equipped for snow. The roofs of all buildings of The Chedi are equipped with snow guards and so-called snow fences. These retain the snow to prevent snow-slides. Auxiliary heating strips are also installed in certain areas. These not only enhance the cosy warmth inside the building; they ensure that melt water can drain off without freezing again.
So the roofs of The Chedi Andermatt are ready for immense amounts of snow. And nobody has to climb up onto the roofs to laboriously remove the snow by hand with a shovel. Nobody? “Not quite! The one exception is the glass roof at the main entrance. When more than two-and-a-half metres of snow accumulates on this roof, somebody must go up there with a shovel”, quips Balzli.
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