The blue green roof – helping cities cope with stormwater

The blue green roof combines blue and green roof technologies. Conventional green roofs conventional use a drainage layer to provide lateral drainage and irrigation. Blue roof technology, however, aims to increase both the volume of water stored and control the amount of water released. Combining the technologies can increase the overall benefits of greening roofscapes. Therefore it is not a case of green or blue infrastructure but a blending of the both.

France - blue green roof
Blue green roof – Oasis by Vegetal ID


Storing rain water – blue roofs

Blue Roofs are not a new idea. They have been around in one form or another for well over 60 years, in the UK, Europe and the US. The roofs are designed to explicitly store rainwater and can provide a number of benefits depending on the design. These benefits include:

  • temporary storage of rainfall to mitigate runoff impacts
  • storage for reuse such as irrigation
  • recreational opportunities.

Blue roofs can include open water surfaces or placed beneath paving or shingle. However, they can also make up the drainage and support layer for green roofs, on both intensive and extensive.

A smart combination – blue green roof

Whilst the water management engineer will be focused on how much water is stored and released, a blue green roof provides wider benefits. Of course a blue roof on its own, is positive, yet it provides only one solution. A blue green roof a wider range of benefits. Accessible roofs that are planted provide amenity. Extensive ones that are encourage wildlife, bring nature back into our cities. And they all help cool cities.

Furthermore, smart technology can manage how water is stored and released. An excellent example of this is Urbanroofscapes and the smart roof project. A series of smart blue green roofs have been built that provide benefits to both stormwater and urban cooling.

Blue-green roof under construction – PolypipeWMS


In the UK, CIRIA are looking to produce guidance on blue roofs. This should also include guidance on combining both green and blue solutions on one roof.