Blue-green roofs can store more rainwater than “normal” green roofs. Under the green layer of plants is a crate system in which the water is stored. The water reaches the plants through the substrate (soil) and a filter layer.

The roofs are equipped with smart sensors and valves. As the sensors measure the water level the valves respond to the weather forecast and open and close at the right time. This is useful when, for example, it is going to rain or when drought is predicted.

It is the first time that the blue-green roofs are used on such a large scale, creating a smart network. The smart roofs will soon communicate with each other, with the roof owners and with the water manager – which is Waternet in Amsterdam. In this way it is possible to accurately determine when, where and how much water has to be drained or retained. A new way of water management in the city!

It is also possible to connect the smart roofs with all kinds of sensors. For example, in the sewage system, so that we know when it is a calm moment to discharge the rainwater. Or sensors that measure the groundwater level, because that also determines what a good time is for rainwater to infiltrate. The roofs collect data for us: how much rainwater is collected in the various neighbourhoods, are there differences between them and how can we use that information?


Different types of vegetation can grow on the roof. Possible types are: moss, sedum, herbs, grasses, ferns, shrubs or a combination. There is a difference between extensive (sedum) and intensive (planting) green roofs.
The planting is rooted in the substrate layer, similar to soil. This layer provides support and nutrition to the plants.
The filter layer prevents particles from the substrate from ending up in the water storage layer and clogging it up. It also ensures an even distribution of the water that can be absorbed by the plants.
The water retention is an extra drainage layer. This layer consists of a lightweight crate system in which rainwater is stored. Here, an integrated fibre technology has been incorporated, which makes water transportation from the storage to the plants possible.
This layer protects the underlying roof construction from invading plant roots and it prevents leaks.
The roof deck, also called roof construction, carries the weight of the roof and provides heat insulation.
By means of this “smart valve” the stored rainwater can be discharged or retained in the drainage layer. This smart valve responds to weather change and opens and closes automatically at the right times.