Cork green roof

Earth Kweek/ Dakdorpen

The Green Roof developed for ‘The Exploded View’ is built of 100% natural modules based on expanded cork, as an alternative to plastic trays. This type of cork is made from the waste material of cork stopper production, which is derived from the bark of the cork oak. 

Four out of five layers of a standard green roof fully or partially consist of plastic.

Made of

  • 52% expanded cork, from Portugal. 100% natural
  • 48% wool substrate, from the Netherlands. 100% natural

Production process

  • The cork residual material is ground into granules.
  • The cork granules are baked into expanded cork in steam ovens, where it expands and binds together through its own resin, suberin.
  • The expanded cork sheets are then sawn and milled into a tray.
  • These modules are filled with a special substrate based on, among other things, natural sheep wool, developed by Dakdorpen.
  • Native flowers and herbs suitable for dry conditions grow in this substrate.


The cork modules are used on flat and slightly pitched roofs of for example houses and carports. 

The application of the cork green roof in The Exploded View Beyond Building is a test set-up in which Dutch wool, which is currently a waste product, is tested as an aggregate of the earth mixture (substrate). Sheep’s wool can keep the other ingredients, compost and ground tiles, airy. The water can also buffer and decay slowly, releasing nutrients for the plants growing in the substrate.

Environmental impact

  • The production of expanded cork is CO2 negative and no chemicals are used. 
  • The cork trees do not die when harvested; after nine to 11 years the bark is regrown and can be harvested again. 
  • The transport from Portugal to the Netherlands comes via either boat or truck, which comes with a yet to determined CO2 emissions. 
  • The wool and compost are recycled and natural products which are collected locally. CO2 emissions are therefore low and no chemicals are used. 
  • The green roof provides nectar and pollen for insects, as well as a shelter and wintering place.

Good to know

The expanded cork offers extra insulation compared to regular green roof materials. Furthermore it has good drainage capabilities which makes an extra drainage layer redundant.


Green roofs are a growing market because of the cooling and water buffering capabilities. The use of natural materials will be worth extra to the clients who often already have a preference for going green. The obstacle is the relatively high price of expanded cork. Furthermore there is more research needed on the long term behaviour of the materials. 

In the set-up for The Exploded View Beyond Building, the effect of wool on plant growth is investigated. Over the roof, from left to right, the wool percentage in the substrate increases from 0 to 50%. In the first two vertical rows, the water buffering effect of wool is examined in comparison with the “standard” recycled textile fibres.