Life cycle assessment of green roofs: A literature review of layers materials and purposes.

Green roofs offer several environmental and social benefits to urban life. However, such roofs require a greater amount of materials than conventional roofs. The life cycle assessment (LCA) is an appropriate tool that has been used to obtain the potential environmental impacts associated with green roofs throughout their life cycle. This paper aims to review the literature related to the LCA of green roofs, responding: which materials and layers were used in green roofs in LCA studies; which processes were considered in each life cycle phase; which types of roofs have already been compared to green roofs through LCA; which measures are taken to reduce the environmental impacts of green roofs; which methods were used to assess the economic feasibility of green roofs over their life cycle and what were the purposes of such analyses; and which LCA studies included public perceptions about the green roofs. Our findings indicate that the materials used in the green roof layers vary among the articles. However, polymeric materials are usually used for all the layers, except for the substrate. Cradle to grave is the most common approach. Within this approach, more than half of the articles considered cooling and heating energy, which may significantly influence the life cycle analysis results. Most studies reviewed agreed that green roofs cause less environmental impacts than conventional and white roofs. The use of byproducts or recycled materials may further improve the performance. In most studies, public perception is not included in the analysis. Regarding the economic approach, both life cycle cost and life cycle cost-benefit are used to compare green roofs economic viability with other roof systems. In addition to discussing studies reported in the literature, this article also recommends future research to improve the performance of green roofs.