A prototype with the hydroactive building façade Hydroskin: The textile building shell is intended to reduce flood and heat risks in cities.
Photo: Hydroskin, Christina Eisenbarth
It is flexible and stable, porous and tear-resistant, the water skin Hydroskin for buildings. “This new material can revolutionize the fight against the effects of heat waves and heavy rain in cities,” says its inventor Christina Eisenbarth. The architect and research associate at the University of Stuttgart wants to use the facades of existing and new buildings to use rainwater collected on hot days to evaporate and thus cool the building. Hydroskin consists of several textile layers that are kept apart by threads.
The system is now being tested in open-air trials: a prototype is currently on the campus of the University of Stuttgart. At a height of up to 36 meters, tests are being carried out to see whether the facade can deliver what the scientists expect from it after hundreds of laboratory tests. Hydroskin is particularly suitable for high-rise buildings because of the large facade surfaces. “Moreover, the rain hits the facade at an angle as the height increases, so that from a building height of around 30 meters, more rain can be absorbed by the facade than by a roof area of the same size,” explains the inventor.
And this is how the product works in detail: The system is surrounded on the outside by a water-permeable membrane, which, according to the university, allows almost all raindrops to penetrate. A film on the inside drains the water downwards. It can then either be stored in a reservoir or channeled directly into the building, where it is available for the washing machine, flushing the toilet and watering plants, for example. When it is hot, the textile facade is moistened with water and thus cools the building and the surrounding urban space through evaporation.
The natural cycle of precipitation and evaporation is disrupted by increasing sealing, as Hydroskin inventor Eisenbarth explains. “Ultimately, we ourselves are turning our cities into heat islands and flood basins.” The sponge city concept is intended to put a stop to this development. It is about the ability of a city to absorb excess water, store this water like a sponge and then release it again at a later time through evaporation or seepage. Hydroskin is also based on this principle.
Stefan Petzold from the German Nature and Biodiversity Conservation Union (NABU) sees Hydroskin as a way to make life in the city more pleasant – just like green facades, greened disused roundabouts and converted parking spaces. “By removing such impervious surfaces, we are giving something back to nature,” says the NABU representative for urban nature. According to Petzold, the example of the Humboldt University in Berlin shows that plants in buildings have economic advantages, as they save 15,000 euros a year through natural cooling instead of air conditioning. According to Eisenbarth, the investment in Hydroskin is manageable: one square meter will cost the building contractors several hundred euros, she estimates.
Wolfgang Schubert-Raab, President of the Central Association of the German Construction Industry, finds the invention “extremely interesting” in light of increasingly unpredictable weather phenomena. In addition to the known and already specially protected hotspots of classic flooding, such as in Passau, there are more and more spatially and temporally unforeseen damage events. Hydroskin can be used flexibly in such situations. “You can’t protect every city from everything,” says Schubert-Raab, but Hydroskin is also suitable for temporary construction and for cooling container daycare centers, for example.
The University of Stuttgart provides some figures: While normal building surfaces can reach temperatures of over 90 degrees under the scorching summer sun, Hydroskin reduces the temperature to as little as 17 degrees. The amount of water absorbed reduces the runoff that flows through sealed surfaces directly into the sewer system and leads to flooding when the absorption capacity is exhausted. According to Eisenbarth, 5.7 square meters of Hydroskin cool as much as a 2,500 watt air conditioner.
The material, which is currently made from reusable polyester and will in future also be made from PET bottles, is also intended to be environmentally friendly. It can also be printed on. “The architect can give the buildings a new, individual look,” says Eisenbarth. She sees no concerns about possible problems with the statics of the buildings – one square meter of Hydroskin weighs just 1.2 kilograms when dry and a maximum of 4.7 kilograms when wet.
The scientist developed Hydroskin as part of her doctoral thesis at the Institute for Lightweight Structures, Design and Construction at the University of Stuttgart. As the founder of a start-up, she wants to quickly transfer the technology into construction practice. The Saarland native already has a buyer: Bavarian building contractor Schubert-Raab says it wants to test Hydroskin as part of a project with new building materials for commercial buildings.
