Austria’s Alpine gem

A CorTen clad chapel strikes an unexpected note deep in the wild Tyrol, but its garnet-like shape gives clues to why it is there

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Poised on a rock spur beside a still lake on a mountain plateau 2km above the Ziller valley in the heart of the Austrian Tyrol, the Garnet Chapel commands a spectacular view in one of Europe’s harshest climates.

The new 700m3 geometric building, designed by Swiss architect Mario Botta, is highly sculptural, its reddish brown CorTen steel-clad facade taking the form of a crystal. 

The idea to build the chapel in the shape of a garnet crystal came from the client, Josef Brindlinger, whose  great-grandfather found several garnets of exceptional purity at the location. The form of a cut garnet features 12 rhomboid surfaces, 14 corners and 24 edges.

‘The chapel was commissioned to enhance the top of the mountain,’ says Botta. ‘It would complement the arrival nearby of a cableway, chalets, a restaurant and other tourist facilities, and remember the local saint, Blessed Engelbert Kolland.’

The facade weighs 17 tons and comprises 12 rhombuses made of 120mm-thick plywood panels clad with 300mm-wide CorTen steel sheets that rest on a total 2,280 threaded rods anchored into the supporting structure. 

Behind the CorTen, the walls and roof have a layer of company FDT’s Rhepanol fk polyisobutylene-based synthetic roof waterproofing membrane. The highly durable product, specified by the project’s partner architect, Besto of Austria, is able to handle the region’s strongly fluctuating temperatures, thunderstorms and very strong winds.

Supplied in the UK by SIG Design and Technology, Rhepanol fk has an integrated synthetic fleece and a prefabricated self-sealing edge, making it very stable, even in strong winds. It is UV resistant and remains flexible at temperatures as low as -60°C. 

The 120mm thick plywood structural panels, while covered with Rhepanol and CorTen externally, are lined with larch internally
The 120mm thick plywood structural panels, while covered with Rhepanol and CorTen externally, are lined with larch internally

‘Due to the harsh conditions, we had to have a waterproof surface within a week of assembling the walls,’ said Besto director Bernhard Stoehr. ‘Rhepanol meant the waterproof surface could be glued ahead of fitting.’

The synthetic membrane contains no toxic plasticisers or halogen fire-proofing agents. It is also fully recyclable.

The builders had just three months to erect the chapel, between the last of the snow in mid-June and new snowfall in September, so the facades were precision engineered off-site and installed in a strict sequence  to achieve structural stability once all 12 elements were held together in tension. 

Local specialist roofing contractor Robert Stadlmeyer carried out waterproofing works on the plywood panels, which were laid flat on the ground. To prevent wind uplift, the membranes were bonded in strips to the supporting timber structure.

The severe weather meant full adhesion sometimes took a day or two, so the Gripfix system was used to provide mechanical fastening – similar in nature to velcro – ensuring elements were ready for installation.

After waterproofing, the threaded rods needed to support the CorTen Steel cladding were anchored into half the panels on the ground. To achieve a fast, accurate and permanent waterproof flashing against these rods, the roofers used FDT’s lightning conductor sleeve with Rhepanol collar.

‘Because we had to screw into the surface 2,280 times to attach the cladding to the rods, we needed a system that ensured every point was safely waterproofed,’ said Stoehr. 

Inside the finished chapel, natural daylight  floods the larch-clad space through a central opening and circles the room as the sun rises and sets. It’s a sight to behold for architects and religious pilgrims alike.

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