The use of natural stones for mitigating urban heat island intensity in LEED® perspective

In recent years, the topic of the Urban Heat Island (UHI) has been increasingly debated due to the problems inherent in the thermal gradient inside urbanized areas. Research is oriented towards the use of green areas, natural and permeable materials or with a high solar reflectance index (SRI), capable of contributing to reducing global warming as related to building and urban environment. The importance of these choices is demonstrated by the recognition of significant credits in the most widespread green building rating systems, including LEED®. However, it is essential for manufacturers, designers and professionals in the construction sector to have adequate information about the performance of their products. In this perspective, this experimental research work is aimed at evaluating the main parameters that contribute to the solar reflectance of products made of natural stone, increasingly used in modern architecture and buildings. Three lithotypes of Sardinian origin, with proven international commercial diffusion, were analysed: Orosei marble, Ghiandone Rosa Limbara granite and Sardinian basalt. For each stone, the most used commercial surface treatments were considered. The results highlight how the surface finish significantly affects the radiation parameters of the tested materials: polished surfaces have low average emissivity and reflectance values, resulting in SRI values that do not comply with LEED® requirements. On the contrary, impact treatments, such as bush-hammering (especially CBH), induce an increase in surface roughness and a consequent greater diffusion of solar radiation, with high SRI values.