A Multi-criteria methodology for comparing the energy and environmental behavior of cool, green and traditional roofs

The reduction of energy demand for space cooling, as well as the mitigation of the Urban Heat Islandeffect (UHI), require adequate solutions at building and urban scale. In particular, the roofs of buildingshave been identified as a possible field of intervention that could contribute to provide significant energysavings and environmental benefits. In this context, cool and green roofs are two very interesting solutions,which may allow obtaining both the reduction of the energy consumption and the improvementof the comfort sensation in the outdoor and indoor environment.This paper presents a numerical comparative analysis of the energy and environmental performance ofthree typologies of roof, namely a standard roof (SR), a cool roof (CR) and a green roof (GR). This analysis,developed through dynamic energy simulations under temperate climate, highlights the differentthermal behavior for the investigated roof scenarios, also as a function of the level of thermal insulation.Moreover, with the aim to obtain a classification between SR, CR and GR in Mediterranean climate, ascoring system is presented, which considers the whole performance of the investigated roof scenariosunder a broad perspective.As a result, it is found that green and cool roofs provide higher energy savings and environmentalbenefits than highly insulated standard roofs. In particular, scarcely insulated green roofs showed thebest performance in relation to the UHI mitigation under the climatic conditions typical of the Mediterraneanarea.