Actual solar reflectance of roof surfaces andstandard energy performance of Italian buildings in summer

Solar reflectance or its complement to unity, solar absorptance, are key parameters to evaluate solar gains through opaque elements and predict summer performance of buildings. For their evaluation, Italian technical rule UNI/TS 11300-1 prescribes a standard approach based on colors, distinguishing between dark-, intermediate- and light-colored surfaces and assigning to each category a fixed value of solar absorptance or reflectance. This approach, however, may be simplistic. In fact, an experimental campaign performed at the Energy Efficiency Laboratory of the University of Modena and Reggio Emilia showed that typical materials for Italian building such as roof tiles, coated tiles, paints or sealing membranes can show similar colors, but very different values of solar properties.In this paper, the calculation method currently in force in Italy for solar gains is briefly presented and then applied to a general analysis. In particular, the range of variability for summer performance of buildings is discussed in relation to the color-based evaluation approach, also taking into account measurement results obtained for some roofing solutions typical of Italy.