In addition to reducing the sealing of agricultural land, the unsealing of urban areas plays an important role in the habitability of European cities in higher summer temperatures. The blue-green infrastructure with various sponge city solutions on roofs, streets and green spaces help to prevent flooding and provide water for vegetation. Shading and evaporation create a cooling effect while at the same time saving irrigation water. This is an important task for urban development and the construction industry – with positive social and ecological effects for cities and their inhabitants.
Text Christian Vondrus
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“Building is always a battle against water in various states of aggregation” – this is the insight of building physics. But we will always lose the battle against water and against nature in the long term. Technology must accomplish this task with water . This is where the solutions of a “blue-green infrastructure” come into play. For thousands of years, buildings and urban planning were built in harmony with water – as no other technical solutions were available – as self-protection against excess water, snow and ice and to secure food and water supplies by storing water in retention basins.
Wikipedia definition of “blue-green infrastructure”
Green infrastructure, also known as blue-green infrastructure , describes a strategically planned network of natural and semi-natural areas with different natural features at different scales. The term was coined in the 1990s in the United States. The innovative concept was intended to provide answers to the environmental problems associated with the rapid growth of American cities. In addition to ecological, socio-cultural, aesthetic and economic aspects, the concept integrates a wide range of socio-political objectives such as climate change, biodiversity and social cohesion.
In principle, the implementation of green infrastructure is aimed at the sustainable use of nature. Green infrastructure is conceptually opposed to gray and brown infrastructure concepts and offers a cost-effective and durable alternative to purely purpose-built gray infrastructure.
Sealing – unsealing
Construction measures over the last 100 years that were not in keeping with nature have led to today’s problem of critical land sealing on the one hand and the necessary redensification in and around conurbations on the other. The unwieldy artificial word ” redensification ” does not describe the actual goal here. 
The public debate on reducing land sealing (land consumption) is mainly based on the argument of lost agricultural land (food security) and the conversion of grassland into building land. More usable habitat on already sealed areas and the unsealing of unused areas or no new sealing of natural areas should be aimed for.
However, unsealing and the tasks of a blue-green infrastructure play an important role for various objectives:
- Response to climate change (heavy rainfall events and long dry periods)
- Local flood protection, infiltration and water retention
- Doping of the groundwater (against falling groundwater levels)
- Rainwater storage to save drinking water for artificial irrigation
- Making rainwater available for vegetation on sealed surfaces
- Mitigation of “urban heat islands” through shading and evaporation by trees
- Socially valuable meeting zones for residents (green lungs of cities)
- Increasing biodiversity
Blue-green infrastructure thus makes an important contribution to meeting all six environmental objectives of the EU Taxonomy Regulation for buildings and urban development. Their implementation is also already anchored at the level of the federal states: for example, the rainwater management of MA 22 in Vienna and the rainwater plan of the federal state of Lower Austria, which provide guidelines for planning and examples of their implementation.
In building practice, however, water management is usually only understood to mean the use of rainwater as service water for toilets and washing machines and the drainage of surface water into sewers, cisterns and soakaways (gray infrastructure). The planning of rainwater management as blue-green infrastructure is carried out by cultural engineers (water planners) when designing the outdoor areas and any greening of buildings.
Sponge city solutions
The collective term “sponge city” is used to describe various water retention measures in urban areas – on roofs, façades, green spaces, streets and squares. Tried and tested substrates for the drainage of squares, streets and parking lots, such as the DrainGarden© system, are used for water retention, especially for trees and shrubs, which quickly infiltrate and filter surface water and store large quantities of water. These can be used instead of soakaways and create usable, shaded green spaces with a high level of biodiversity.
In order to prevent the immediate discharge of surface water and to enable the replenishment of the groundwater reservoir, most federal states require the infiltration of rainwater on private land and water retention on green roofs.
For water retention on green roofs (retention roofs), tried and tested storage substrates with different water capacities and also solutions with automatically controlled water management are available.
To prevent root growth from destroying the roof waterproofing, biocide- and pesticide-free root protection membranes with mechanical root protection should always be used for green roofs. Root toxins are flushed out of the membranes over many years and pollute groundwater and sewage treatment plants and, in the case of local seepage, your own ground for many years. Solutions from various suppliers are available for this purpose.
Products with OIB technical approval enable a structure with only two layers of waterproofing, even with intensive greening, where otherwise three layers with chemical root protection would have to be applied. This saves money and protects the environment by avoiding the use of environmentally harmful substances – a real win-win situation for people and nature.
Summary
Blue-green infrastructure solutions thus make important contributions to all six environmental goals of the EU taxonomy, enable additional eco-points for building certifications, create socially and ecologically valuable living spaces and represent an important task for urban development and the construction industry.
