A simple methodology for comparing cost-benefit of traditional, green and cool roofs

Energy policy makers, architects and researchers, when designing new buildings or rehabilitating the existing ones, are engaged in the attempt of limiting the energy needs for climatization (NZEB buildings) and the environmental pressure exerted by buildings (EU Climate Action). The pursuit of this demanding assignment calls for innovative solutions in conceiving the building envelope and its energy systems. Recently, among the most effective tools for improving the energy and environmental performances of buildings, the technical interventions regarding the roofs are gaining a rising attention. Indeed, covers of buildings are responsible of a relevant part of their energy losses and, on the other hand, could contribute to increasing the UHI effect. In the paper, a simple methodology that compares the energy and environmental benefits of cool and green coverages with traditional ones is presented. The capability of limiting the UHI effect of these solutions is also analysed. The methodology is applied to four cities of the Sicilian Island, characterized by different building density and different microclimates. This in-field application shows the feasibility of the method to be used in different urban contexts, as a useful contribution to the design of new buildings or to the re-design of the existing ones.