LAUSR

Abstract Outdoor and indoor thermal comfort in the built environment is a crucial factor impacting urban heat island (UHI), building energy consumption and occupant welfare. Building roofs are directly connected to these phenomena since high overheating on both surfaces can affect negatively all these aspects. Several innovative technologies, such as phase change material, green and cool roofs and so on, were proposed and investigated to address these environmental targets. However, an accurate design of traditional roofs is required to limit the use of these technically complex and expensive technologies. The main objective of this work is to study the role of the inclination and azimuth (orientation) of lightweight and heavyweight roofs, equipped or devoid of an insulation material during the cooling period in Italy and Greece. The investigation was carried out by means of a dynamic model in a steady periodic regime proposed by the authors that accurately takes into account all the building roof heat exchanges. The surface temperature fluctuations, in terms of amplitude and maximum peak, were employed to find the optimal configurations to mitigate the UHI effect and cooling load. In addition, the temperature decrement factor and time lag were used to summarise the overall roof thermal behaviour. The results showed that an accurate roof design leads to a reduction of the amplitude and maximum peak of the temperature on the external surface of 12.5 °C and on the internal surface of 4.7 °C. Instead, the decrement factor varies also of 29.9 % and the time lag of 7 h.