Laboratory study on the potential use of recycled inert construction waste material in the substrate mix for extensive green roofs

Green roofs, defined as roofs of buildings that are partially or completely covered with vegetation planted in a growing medium can provide multiple sustainability benefits. There is potential to increase the sustainability benefits of green roofs by using recycled construction materials for green roof construction.This study investigates the viability of using recycled aggregates in the substrate mix for extensive green roofs where a ‘carpet’ of plants is supported by lightweight growing media (substrate) overlying a drainage layer. We investigated the adequacy of recycled inert construction waste as a growth medium, the drainage properties of the substrate mix containing recycled materials as well as its susceptibility to erosion and resistance to sliding when placed on a slope.In this laboratory study we compared the establishment, development and performance of both grass and sedum model green roofs under simulated rainfall and found that the substrate mix containing recycled construction waste materials was adequate in supporting plant growth, was resistant to erosion and slippage and capable of providing good drainage. When vegetated, the ‘green roof’ can provide attenuation of the drainage water with magnitude depending on the type and percentage of vegetation cover.We attempt to put the results of this small scale laboratory investigation on extensive green roofs into the wider perspective of sustainability benefits offered by the green roofs.