Vertical water sponge - vertical water retention systems for protection against heavy rain and extreme heat

Climate change in recent years has led to an increase in intense heavy rainfall events and heat waves in cities. Heavy urban sealing and densification have resulted in high water levels, flooding and heat waves with droughts, causing great damage to people and nature. Important countermeasures are being bundled worldwide under the sponge city principle. These aim to transform cities, create more green-blue oases and opportunities to retain rainwater and divert it from the sewage system – for example, through unsealing, green roofs or the construction of retention basins. This often requires complex construction measures, some of which are associated with higher costs and greater effort. Fraunhofer UMSICHT has developed a vertical retention system with a mineral water storage tank that can be installed on facades, for example. This allows vertical surfaces to be put to optimal use, even in densely populated areas.

A demonstrator of the newly developed retention module is cuboid in shape and contains perlite, a mineral material that stores water from building roofs during heavy rainfall. The permeable outer shell of the modules is made of aluminum, e.g., perforated sheet metal. The water-storing modules are connected to the roof drainage system and can be placed on top of or next to each other and attached to a building facade. Water storage not only reduces the load on the sewage system, but also improves the microclimate through evaporative cooling. This also counteracts urban heat islands and supports the local water cycle. The previously unused vertical surfaces of buildings are put to good use, and rainwater is stored instead of seeping away. The concept is suitable for both new and existing buildings.

Fraunhofer UMSICHT has developed a test rig for a roof area of 1 square meter, filled with 100 liters of perlite (dry weight 8 kg) and a volume flow of 40 liters per hour (corresponding to heavy rain index level 6-7/exceptional heavy rainfall or a return period of 50-100 years), which demonstrates the high performance of the water storage tanks. A unit is installed between the roof water and the retention bodies to regulate the volume flow of the inflowing water.

It is possible to adapt the design of the modules to the overall architectural appearance. The modules can, for example, be installed as a front facade. The module surfaces can also be further functionalized, e.g., for greening or the air conditioning of buildings or noise protection.