Comparative cradle to grave environmental life cycle assessment of traditional and extensive vegetative roofs: an application for the Lebanese context

Abstract

Vegetative roofs (VRs) are fully planted roof spaces that offer aesthetic view, storm water management, sound insulation, energy savings, and air improvement. The aim on this work is to compare the life cycle environmental impacts of traditional gravel ballasted roof (TGBR) and extensive green roof (EGR) each having a surface area of 650 m2. Environmental impacts were determined and analyzed using a cradle to grave life cycle assessment (LCA) including two end-of-life scenarios (landfilling and recycling). In particular, for the use phase, the updated Lebanese electricity grid was integrated for the first time in the LCA software SimaPro and real-time temperature monitoring for TGBR and EGR roof mockups that were installed on the rooftop of the Chemical Engineering Building at the University of Balamand-Lebanon were used. Life cycle impact assessment was performed using the IMPACT 2002+ methodology for all impact categories except for water scarcity, which was determined from the water use in life cycle assessment (WULCA) consensus model. Results demonstrated that the assembly and the use phase were the highest contributors to the environmental impacts for TGBR and EGR. Comparing the two types of roofs, TGBR had the highest contribution for all impact categories except for “land occupation.” This is justified by the presence of the vegetation layer in the vegetative roofs. EGRs are more efficient than TGBR from an environmental perspective. Moreover, increasing the share of renewable energy in the total Lebanese energy production will lower greenhouse gases emissions from the energy sector and the other life cycle environmental impacts.