Context

Extreme heat and heavy rainfall events with severe inundations have a significant impact on urban architecture, resulting in considerable personal injuries and material damage. Nowadays, the proportion of façade surface areas in urban environments with tall buildings is immense, thus offering a high leverage effect on climate resilience and sustainability of buildings and cities can therefore be attributed to the building envelopes.

Ongoing urbanization and re-densification raise the percentage of sealed areas and increase the risk of flooding in urban areas. Sealed areas with runoff effect are connected more and more to the existing sewage infrastructure. Therefore, the hydraulic capacity of conventional sewage systems is often exceeded in case of heavy rainfall events leading to a risk of flooding with significant material damage and personal injury. The consequences range from selective overflow in road space to severe flooding of entire streets and damages to infrastructures and buildings. Re-dimensioning the existing sewage systems, if at all possible, would entail a huge amount of work and costs.

Additionally, the absorption of solar energy on sealed road and building surfaces in the city leads to a significant increase of air temperature, which will analogously rise in the future due to global warming. So-called "Urban Heat Islands" are generated that, apart from heat stress, pose a health hazard especially to older people. Both extremes - flooding and heat stress - are further amplified by climate change. According to forecasts, increased heavy rainfall events with intensities far above the prescribed rainfall limits as well as a significant temperature rise with coherent increasing number of hot days are to be expected in the future. Retention areas for decentralized infiltration of rainwater are therefore urgently required particularly in dense urban zones. Acutely needed are concepts for decentralized rainwater retention and water evaporation, which contribute effectively and economically to an improvement of urban rainwater and temperature management to be applied on building surfaces and other civil engineering structures with a minimum amount of embodied mass, energy and CO2 emissions. In this context, textile and foil based HydroSKIN elements offer an immense potential.

While social developments lead to increasing urban densification, surface sealing, and the construction of high-rise buildings, the effects of climate change, such as extreme heat and heavy rainfall, require the opposite: the creation of more infiltration and buffer areas for reducing “urban heat islands” and inundation risks. Two complementary approaches to climate resilience are being pursued to protect against and respond to climate challenges: climate mitigation by reducing emissions, as well as climate adaptation for reducing or avoiding damage. The combination of climate mitigation and adaptation strategies, by addressing both climate challenges of heat and inundation risks, is seen to have great potential for dealing with the global environmental issues in a sustainable way. Whereas most existing façades are designed to provide only minor qualities at a district or urban level, HydroSKIN provides a decentralised absorption of wind-driven rain hitting the building façade, its targeted use inside the building to reduce water and energy consumption as well as time-delayed release of water in heat periods to cool the interior and exterior environment by evaporation.