Long term experimental analysis of thermal performance of extensive green roofs with different substrates in Mediterranean climate

Green roofs are passive construction systems that can contribute to reduce the energy demand of buildings and achieve the European goal of nearly zero energy buildings. The main objective of this work was to determine experimentally the thermal performance of extensive green roofs with different substrates, compared to a traditional gravel ballasted roof. Hence, a study on the annual reduction of energy demand throughout two years warmer than average years, 2016 and 2017, and a dynamic analysis based on decrement factor, DF, time lag, TL, cooling potential, CP, for these three green roofs were carried out. The results showed that significant reductions of DF and increases of TL and CP were achieved, especially in the green roof with 100% of commercial growing medium substrate. Annual reductions of energy gains and losses were obtained in the three green roofs, with annual average reductions of 66% and 63%, respectively, compared to the traditional roof. These results were mainly related to the composition of the substrates, their capacity to retain water and the quantity of vegetation in each plot This study indicates that the use of green roofs contributes significatively to reduce the energy demand of existing buildings under warm climatic conditions. (C) 2019 Elsevier B.V. All rights reserved.