Life cycle assessment of layers of green roofs

Recent years have seen an increase in the amount of green roofs in urban areas across the world. The research to date has tended to focus on the general advantages of such roofs while less attention has been paid to environmental impacts of the layers used in the construction of green roofs. In this paper, the environmental performance of two complete lightweight green roof systems were analyzed with the aim of determining the potential environmental impact of the different layers of the systems. The results show that among the materials we analyzed, the water retention, drainage and substrate layers contained the components that had the greatest negative environmental impact. More specifically, our results show that when the required performance is not impaired 1) Rockwool, virgin HIPS and expanded clay should be avoided in order to produce environmentally responsible roof systems; 2) simple roof systems may be recommendable whenever feasible and 3) recycled and local materials are better than virgin and those requiring long distance transport; and 4) the use of compost on the roofs may be recommendable if taking into account that using organic waste in landfill is a worse scenario than composting it.