Cradle-to-gate Life cycle assessment of traditional gravel ballasted, white reflective, and vegetative roofs: a Lebanese case study

Abstract

Lebanon, a Mediterranean country, lacks a clear sustainability plan as well as an infrastructure update and management, leading to road flooding, especially in urban areas. Therefore, the installation of Vegetative Roofs (VRs) could be an interesting option for Lebanon. To evaluate if VRs are truly superior to Traditional Gravel Ballasted Roofs (TGBRs) and White Reflective Roofs (WRRs), a cradle-to-gate Life Cycle Assessment (LCA) was performed. Potential environmental impacts of an existing Extensive Green Roof (EGR) were compared to three fictitious roofs of the same area: TGBR, WRR, and Intensive Green Roof (IGR). The functional unit used for comparison was: "providing a cover for a surface area of 834 sqm and for 45 years". Specifications of TGBRs and WRRs were provided by local technicians and civil engineers. Furthermore, specifications of VRs were provided by the United Nations Development Program (UNDP), Country Energy Efficiency and Renewable Energy Demonstration for the recovery of Lebanon (CEDRO) project. The SimaPro software and Ecoinvent library were used to model the systems considered. Results clearly indicated that EGR was the best option for all environmental impact categories. Rebar, concrete, and thermal insulation were the main contributors to the environmental impacts for TGBR, while rebar, concrete, thermal insulation, and waterproof membrane were the highest contributors for WRR. Sensitivity and uncertainty analysis were also performed to verify the robustness of the results.