Innovative sponge city project: First Detention Roof based on the Purple Roof Roof concept

Germany's first Detention Roof was installed at an elementary school in Schauenstein, Bavaria, in September 2023. This water-storing green roof system is also known as a Detention Roof and is based on the Purple Roof concept. The project is part of a larger Sponge City project: an innovative solution for water management. Sempergreen is the developer and supplier of the Detention Roof concept, which was developed in collaboration with Browatech from Geroldsgrün (developer and supplier of the core technology of the Detention Roof: the drainage layer) and Knauf (Urbanscape Green Roll). The Detention Roof extends the conventional green roof into a rainwater management tool. The rainwater run-off is controlled in such a way that it drains away more slowly and prevents flooding.

Sustainable urban development: How sponge cities are revolutionizing water management

Effective measures to better control and use water in times of climate change are a hot topic. A sponge city is a revolutionary planning idea based on the idea that cities can function like sponges by capturing, storing, filtering and reusing excess rainwater. The Detention Roof is an effective rainwater retention and delayed drainage measure that fits perfectly into the sponge city concept. As technologies evolve and awareness of sustainable urban development increases, sponge cities are expected to play an increasingly important role in future urban planning.

What is the Detention Roof concept?

Climate change is leading to an enormous increase in heavy rainfall. As a result, flooding in urban areas is causing major damage. The Detention Roof concept was developed to make a significant contribution to water management in urban areas.

The Detention Roof consists of four layers. Each layer has its own effect that ensures optimum results:

• Sempergreen® Sedummix mat: the top layer consists of vegetation mats, pre-cultivated with 6-8 different sedum species.
• Knauf Urbanscape® Green Roll: this water-absorbing intermediate layer absorbs the water completely evenly over the entire roof and also serves as a growth layer for the vegetation mat.
• Sempergreen Storage Layer HC40/60: this intermediate layer with honeycomb structure serves as a temporary water column in the event of extreme precipitation. By working together with the underlying detention layer, the water can be temporarily stored in this layer.
• Sempergreen detention layer T5: This bottom layer is the retarding factor in the whole. The layer consists of thousands of threads that have been machine-stitched next to each other. In combination with the hydrophobic underside, these seams ensure that the water is pushed up into the storage layer by friction. Excess rainwater can thus be held back for up to 24 hours or longer. The length of the delay depends on the exact project specifications.

Thanks to its design, the Detention Roof can temporarily retain rainwater and slow down runoff even when it is completely saturated. The aim of the concept is therefore to allow the stored water to run off only gradually in order to prevent flooding and make previously required retention basins or similar superfluous or smaller.

New Sponge City Competence and Transfer Center officially founded

At the end of 2023, Browatech and Sempergreen were present at the INWA (Institute for Sustainable Water Systems at Hof University of Applied Sciences) water symposium. At this information event, the focus was on the sponge city and the new Sponge City Competence and Transfer Center was officially founded. The Schauenstein project was also presented as an example project. The Hof Water Symposium was aimed at specialists from the water management sector as well as the press, local authorities, planners, architects and garden and landscape designers. Following the day's program, Sempergreen and Browatech presented the Detention Roof - Germany's first green roof based on the Purple Roof concept - and talked about the advantages and possibilities of a green roof. Many participants took part in a four-way discussion and asked questions about the project and various green roof concepts.

Since then, many municipalities have been working on the concept and inwa regularly reports on its website about the measurement results for soil moisture, rainfall and (air) temperature.

Would you also like to follow the measurement results of the first Detention Roof based on the Purple Roof concept?

Then please click here

Note for editors

About Sempergreen®

Sempergreen, headquartered in the Netherlands, is the world's largest producer and supplier of innovative quality solutions for green roofs, green facades and prefabricated ground cover. For Sempergreen, creating a green and liveable world is the indispensable basis for our generation and the generations to come. Sempergreen's green solutions contribute to reducing the impact of climate change and pollution. In order to minimize its ecological footprint, Sempergreen supplies as much as possible from local nurseries in Europe, North and South America and Asia. Sempergreen's highly motivated and professional team of over 200 employees is constantly working on the quality of its sustainable products. Together with its customers, Sempergreen wants to make the world a little greener every day.

For more information about Sempergreen, please visit www.sempergreen.com.

For further information please contact:

Claudia Tomsits, Trade Marketeer DACH, claudia.tomsits@sempergreen.com, phone: +31 (0)343 539699