The "Friendly Alien" in Graz – one of the most famous representatives of blob architecture. (Copyright: Zepp-Cam.)
Products - June 2024

Pluvia now simply goes round and round

Geberit roof drainage

Planning complex roofs with Pluvia roof drainage is becoming more efficient. Thanks to new calculation options in the Geberit BIM plugin, pipes can now be planned with free angles.

“Friendly Alien“ – this is what architects Peter Cook and Colin Fournier call their unconventionally constructed Kunsthaus Graz. The Alien nestles in its rounded splendour between the tiled roofs of the old town. Meanwhile, the Geberit drainage system on the roof performs at its best when it rains.

No rough edges
Planning the pipework was a particularly complex piece of work. As one of the most famous representatives of so-called blob architecture (blob means drop or blob), the Friendly Alien is designed with virtually no corners or edges. “The pipe had to run exactly along the building envelope,“ recalls Harald Hofko, Product Manager for piping systems at Geberit in Austria. However, the standard planning of a Pluvia roof drainage system was only possible with 45 and 90 degree angles in the planning software. “In the building, however, 9 or 12 degree angles were sometimes necessary.“

Every deflection of the pipes leads to a pressure loss. For a negative pressure system to function perfectly, these pressure losses must be calculated precisely. Until now, each construction project with free angles had to be calculated separately. “In cases such as the Kunsthaus Graz, Geberit hydraulics specialists had to make complex individual calculations to enable an installation with different angles,“ says Franziska Knapp, International Product Manager for Pluvia. “This was both costly and time-consuming.“

Geberit tested Pluvia with different free angles on the roof of its own headquarters.

An algorithm helps
Now these individual calculations are a thing of the past. Pluvia can now be planned digitally with free angles using the BIM plugin. “First and foremost, we developed a new algorithm,“ says Franziska Knapp. To do this, experts from hydraulics, digital construction, sanitary engineering, product management and other areas had to work together. “We developed a formula and tested it in practice. We built a system with free angles on the roof of our headquarters to test it,“ says Franziska Knapp.

This has enabled the algorithm to be further improved. “The revised BIM plugin increases the application possibilities of the tried-and-tested system and makes the planning of architecturally complex buildings much easier,“ says the product manager.


The Geberit Pluvia negative pressure roof drainage system utilises small pipe dimensions that fill completely with water during heavy rainfall. This creates a closed water column in the pipe, which leads to a natural negative pressure and at the same time ensures a high drainage capacity. This is Know-How Installed.