Biodiversity impact assessment of building's roofs based on Life Cycle Assessment methods

To fight against the biodiversity loss and to take advantage of ecosystem services that nature can offer, urban planners integrate green spaces in urban projects. However to assess green spaces, attention is generally paid to local biodiversity (i.e. in situ) which concerns the plot on which buildings are constructed. The biodiversity impacted outside the construction site (i.e. ex situ) which concerns the extraction of materials, transportation and waste, is rarely associated to the project assessment. In this study, two endpoint Life Cycle Assessment (LCA) methods are applied: ReCiPe 2016 and Impact World + to assess a conventional roof and three different types of green roofs. As Life Cycle Inventory (LCI) data about urban plants are missing, we created new data to model the vegetation layer of green roofs by collecting information nearby plants nursery. This work shows that 1) extensive green roof generates the least biodiversity loss, 2) ex situ biodiversity is 10 times more impacted than in situ biodiversity, 3) the impact of the vegetation layer on the biodiversity loss is significant. LCA methods do not enable to cover all pressures threatening biodiversity and they also lack precision to assess in situ biodiversity. Nevertheless, their main strength is to consider ex situ biodiversity along the value chain of the studied systems. Coupling LCA with ecological expertise should improve the assessment by taking into account local specificities and both negative and positive impacts of a system (e.g. in situ biodiversity gains with green roofs).