Blue-green roof system for active cooling, urban biodiversity and lower rainwater runoff

Gijsbert Cirkel MSc PhD, Ruud Bartholomeus PhD MSc

  • Start date
    01 Dec 2015
  • End date
    31 Dec 2018
  • Principal
    TKI Watertechnologie
  • collaborating partners
    Drain Products Europe, Creative Industries, Bureau Marineterrein Amsterdam, Ingenieursbureau Amsterdam, Waternet

Heat stress is a growing problem in the urban environment. Industry, real-estate managers and government are working in this project on optimising the cooling function of evaporation from blue-green roofs. The project will produce a widely applicable roof system, as well as unique measurements of the water and energy balance in blue-green roofs. The system will moreover use more diverse vegetation types and contribute to decreasing rainwater runoff levels.

Cooling the urban environment with an optimally evaporative blue-green roof system

Heat stress in the urban environment is a growing problem worldwide. By evaporating water, plants can make a significant contribution to lowering air temperature. Green areas are however quite limited in cities, and temperatures can rise sharply and negatively effect the living environment. Given the huge surface they represent, roofs have the potential of making a great contribution to the greening of a city and to making it climate-robust.

That green roofs are technically feasible and roofs can be covered in lush and flowering vegetation is no longer news. Conventional green roofs tend however to be planted with species that are economical with water and have low transpiration levels. The cooling function of such roofs is therefore minimal. Planting other types of plants is possible, but this requires a thick, and therefore heavy, granulate layer, which is frequently not technically possible in today’s buildings. In this project we are developing a system which optimises the water supply to the plants, and thereby minimises the thickness and weight of the required granulate layer, leading to a maximal cooling rate and a lowering of rainwater runoff levels.

Optimisation and validation of passive irrigation system for urban cooling with blue-green roofs

In this project we optimise and validate a passive irrigation system in which water, via special fibres, is recirculated in a capillary manner to the substrate layer if the plants so require. In this way the plants, in contrast to conventional systems, can optimally transpire over the long term, and thereby contribute to cooling the urban environment.

An essential element of the project is the quantification and scientific underpinning of these properties. To this end, measurement instruments are being developed for specific application to roofs in urban areas. By setting up test plots and conducting innovative measurements using advanced lysimeters – which are specially adapted to the roof environment – the water and energy balance of the different variations of the system will be studied closely.

Less heat stress thanks to cool roofs

The objective of the project is to improve the cooling properties of green roofs in urban areas. A roof system is being developed which, thanks to its lighter weight, can be used more widely in today’s urban areas, and will contribute optimally to the cooling of the urban environment and to reducing heat stress. Furthermore, the innovative measurements will contribute to our knowledge of the urban water and energy balance.