“Remove all asphalt from the roof”

News - 19 March 2018 - Communication BK

Newspaper De Telegraaf recently headed that we should get rid of all flat roofs. That is not the case. It is all about the materials on top of those flat roofs. Many of the roofs in The Hague are materialised with bitumen. During the summer, these roofs can heat up onto 60 degrees Celsius. It would definitely be better to get rid of all asphalt from roofs, conclude researchers Frank van der Hoeven and Alexander Wandl of BK Bouwkunde TU Delft in the report ‘Haagse Hitte: Het Haagse warmte-eiland in kaart gebracht’.


The urban heat island effect plays an explicitly important role in the city districts of Centrum, Scheveningen, and Laak. The urban heat island effect is strongly influenced by the built environment: paving, a lack of reflection of sunlight on roofs (albedo value), lack of greenery, surface water, and shadow, but also building volumes, sky-view and the distance to the sea are all factors influencing the urban heat island during the summer.

The Hague can take several types of action in order to prevent the effect of the urban heat island: 

  • Phasing out the use of bitumen on roofs;
  • Reducing paving;
  • Greening inner areas of building blocks;
  • Cooling of care buildings;
  • Monitoring overheating of dwellings;
  • Preserving buffer zones;
  • Creating green icons. 

In practice, rules will have to be composed in order to create cooler roofs: white, green, or PV, but phase out bitumen. Greening inner areas of building bloks can become a reality when the city works together with its citizens, plant trees in their gardens. Finally, collaboration with suppliers of smart monitors can help to identify the overheating of dwellings even better.

More information

The research Haagse Hitte is part of a series of researches executed by Franklin van der Hoeven and Alexander Wandl. The entire research reports for the investigations into heat islands for the cities of Den Haag, Amsterdam, and Rotterdam are open access available at BK Books (Dutch only):