Thermal performance assessment of extensive green roofs investigating realistic vegetation-substrate configurations

Green roofing is a sustainable solution for building energy saving, urban heat island mitigation,rainwater management and pollutant absorption. The effectiveness and performance of green roofsdepend on layer composition and properties. The uncertainties surrounding green roof performancemodeling are mainly related to the vegetation and substrate layer, which are subjected to surroundingclimatic conditions. Energy simulation software typically does not use validated models encompassingall possible combinations of vegetation layers and substrates. Therefore, the objective of this researchis to investigate different extensive green roof solutions for assessing thermal performance and toprovide information on vegetation and substrate layer design. Different simulations executed inEnergyPlus were carried out based on realistic literature data drawn from previous experimentaltests conducted on plants and substrates. Several combinations (30 plant-substrate configurations,six vegetative species and five types of substrates) were defined and evaluated. Furthermore,indexes based on the surface temperatures of green roofs were used. Finally, a comprehensiveranking was created based on the scores to identify which extensive green roof combinations offeredthe highest performance. Greater plant heights, LAI values and leaf reflectivity values improvegreen roof energy performance in the summer more significantly than substrate modification.During the winter, thermal performance is more heavily dependent on the substrate if succulentvegetation is present, regardless of the substrate used. These results could provide designers withuseful data at a preliminary stage for appropriate extensive green roof selection.