Innovative rainwater management: weather app controls drainage from green roof

Around 74 hectares of natural space is sealed off in Germany every day. These areas are disappearing from the natural water cycle over the long term. The drainage system is outdated and insufficient in almost every town and city. Investments and expansions in the existing system are very costly and are thus avoided. The more affordable solution is to restrict the discharge permitted into the overloaded drainage network. What’s more, flooding verification in accordance with DIN 1986-100 has increased in importance over recent years. The quantity of water produced should be verifiably retained on one’s own property without buildings becoming flooded. 

Optigreen international AG has kept abreast of these developments and developed the flow control-type “retention roof” system solution in the versions “green roof” and “public roof”. This means there are now innovative solutions for setting a specified maximum discharge and to thus observe the restriction on discharge into the drainage system. The basic principle is as follows: on a roof, a water reservoir (storage area) is created over which either a green roof or a public area is installed. This means there is retention space plus the additional use of the roof with a green or public area. The basis of the system is the water retention box WRB, which allows a possible water storage volume of up to 140 litres per square metre to be created. Due to the integrated capillary system, the temporarily stored rainwater from the water retention box WRB is guided into the green structure and evaporates via the vegetation – with the positive effects associated with this. The “flow control system”-type retention roof allows the maximum drainage rate to be set and controlled to up to 1-10 l/s x ha. The accumulation level can be calculated exactly using the rainwater simulation programme RWS 4.0.

But that’s not enough; Optigreen international AG is now presenting the patented flow control system 4.0 “Smart Flow Control”. New developments such as more precise weather forecasts, combined with a weather app-controlled flow control system, open up new technical possibilities for exploiting the retention potential of roof greening in a significantly better way. The functional principle behind the flow control system 4.0 “Smart Flow Control” is as follows: As much rainwater as possible is stored in the water retention box and supplied to the vegetation via capillary columns. Delayed discharge only happens when the reservoir is full. Otherwise, the water is available to the plants as described above. If rain is forecast, the flow control system 4.0 “Smart Flow Control” uses a weather app connected to the Internet to ensure that the outlet is open and the reservoir on the roof is once again sufficiently available to hold the predicted amount of rain. If, for instance, 35 mm of heavy rain is forecast, the flow control system 4.0 “Smart Flow Control” releases just this much water beforehand. Discharge from the roof thus usually only takes place before rain – so when the drainage system is not (yet) under pressure. When it is raining, pressure is take off the drainage system by rain being retained in the water retention boxes on the roof.

As the flow control system 4.0 “Smart Flow Control” can not only be monitored and controlled automatically but also manually from a distance, this opens up whole new possibilities for local and national water management. If many roofs in a city are fitted with this technology and these are linked together, the rainwater supply and the flood prevention systems can be comprehensively and actively controlled. In this way, every city gains the opportunity to establish a large controllable rain overflow basin on different yet interconnected roofs in the city.

info[at]optigruen[dot]de (Webcode "web244")

Photos and Illustrations

Photo 1: The new retention box WRB-F - the centrepiece of the flow control retention roof system solution. Water retention plus greening
Photo 2: Real-life example: Flow control-type retention roof with greening and public areas in Berlin
Peter Küster, Director Applications Engineering at Optigreen Germany with the GaLaBau Exhibition's innovation medal for the new Optigreen System Solution Retention Roof Type Flow Control 4.0 Smart Flow Control
Fig. 1: New: the Optigreen "retention roof” system solution with the weather app-controlled flow control system 4.0 "Smart Flow Control"
Fig. 2: Functional principle behind the flow control system 4.0 “Smart Flow Control”
Fig. 3: The information brochure for the flow control-type “retention roof” system solution. Request for free at

Photo credits "Optigrün". Thank you!