Comparative Study of Different Crassulaceae Species for Their Potential Use as Plant Covers to Improve Thermal Performance of Green Roofs

Abstract

The presence of green roofs in urban areas improves the energy efficiency of buildings; contributes to the capture of CO2, decreasing pollution; and improves the appearance of cities, increasing their sustainability. Additionally, green roofs must include plant species with low requirements and maintenance, and thus, succulent species could be useful in Mediterranean semi-arid regions. In this work, the thermal inertia and the effect of different succulent species as thermal barriers on mitigating the increase in temperature inside experimental compartments were studied in comparison to conventional covers used in the Spanish Mediterranean for a whole year. In general, green covers were more efficient than conventional ones for controlling temperature. Thus, temperatures under green covers were up to 8 °C lower than conventional covers and 3–5 °C lower than the ambient temperature at noon on summer days. Furthermore, significant differences were found between green covers. Thus, despite having high thermal inertia, Aptenia cordifolia showed the worst temperature records, while Aeonium arboreum was the most efficient at mitigating temperature changes both on cold winter nights and hot summer days—even better than Sedum spp., a usual succulent used commercially. Our results demonstrate that succulent species are efficient materials to use as green covers to improve thermal conditions in buildings in Mediterranean cities. This also suggests that the mixture of succulent species (i.e., not only made of Sedum spp.) with different colors and textures could beautify green roofs without compromising their energy efficiency.