Investigating the relationship between surface roughness and reflectance properties of building materials

Materials used in the exterior envelope of buildings and open urban surfaces, in general, strongly affect the urban thermal balance, determining the general magnitude of urban overheating. The surface temperature of reflective materials varies as a function of physical and geometrical properties. Quantifying the influence of surface roughness on reflectance properties has crucial relevance since reflectance can significantly affect the reduction of the absorbed solar radiation and, in turn, the energy demand for cooling. Through an experimental and statistical investigation, this research aims to analytically assess the impact of surface roughness on the reflectance and thermal performances of building materials and, in turn, the role that roughness could play towards urban cooling and mitigation. Results show that the surface's different roughness affects the sample's reflectance coefficient, leaving it basically unchanged in the Ultraviolet and Visible ranges but with appreciable differences in the Near-Infrared wavelengths. This outcome confirms the correlation between the surface roughness and the optical and thermal characteristics of the building materials, making evident the importance of the study of superficial topography towards the mitigation of Urban Heat Island phenomena.