Another application in roof insulation is "green roof". By applying this method not only the energy consumption will be lower but also it will help the environment. The thickness of the boards depends on the type of the green roof applied. It consists of five main layer starting with the bituminous water proofing layer which is applied on the concrete roof deck. Then the Synergy XPS insulation boards are installed which prevents it from being cracked an blistered. On top of XPS boards, the drainage layer is installed which avoids further penetration of water to the layers underneath and provides more insulation. Finally filter layer and growing media depending on the green roof type are installed.