Lightweight fabric roof covers glazed café façade

Café Lichtblick may be Innsbruck’s favorite hot spot.

High over the roofs of Innsbruck, Austria, on the rooftop of City Hall, sits the café and restaurant Lichtblick (“bright spot”). True to its name, the café’s lucid and open structure has unencumbered sightlines of the sublime mountains surrounding the city due to a glazed façade made of curved laminated glass that carries all vertical loads. Consequently, there are no columns to disturb the views.

Designed by French star-architect Dominique Perrault and constructed by KFM GmbH and covertex GmbH, the café’s lightweight fabric roof resists heavy snow loads in the alpine winter and rain in the summer. The approximately 100m² PVC-PES fabric funnel-shaped roof covers the round, totally glazed pavilion. The low point of the fabric membrane is anchored to the floor and has a traction rope pulling upward. On one hand, the low point serves to brace the roof, and on the other hand it allows rain and melting water to drain. The floor anchor is a compensator construction with two pneumatic springs that knuckle under during wind stress. While experiencing a snow load, the anchor pulls down the low point and consequently the roof, thus eliminating the danger of forming a snow sack.

This is the first project to use a pre-stress system based on a flexible gas pressure cylinder system at the low point of the membrane.

Formfinding of a relatively flat membrane geometry that combines both water drainage and snow-load distribution was a challenge. Moreover, the detailed engineering of the membrane connection to the outer horizontal pressure beam, the membrane fixation at the low point in the middle axis in combination with an invisible water draining system, and the pre-stress system in the low point with a gas pressure cylinder system all required high technical knowledge and experience.