Modelling solar disability glare reflected off modern building facades

Abstract

Buildings can be examined during concept design to identify potential for sunlight to reflect off exterior cladding surfaces and create traffic disability glare onto surrounding roadways. Historically most assessment methodologies calculate veiling luminance hazard at roadway receiver locations assuming specular type reflections off glazing. A population dosage of veiling luminance is proposed in this paper as a disability glare risk measure. Modern facades are increasingly adopting metal sheet cladding products displaying both specular and highly diffuse reflective properties. In-house software has been developed to perform solar reflection calculations off a range of specular and diffuse reflective surface finishes. The program generates view-based luminance renderings at traffic receiver locations. Subsequently, a custom script evaluates the renderings and determines annual disability glare metrics including retinal irradiance, glare source angle and background luminance for comparison with existing disability glare criteria. Threshold increment is calculated from modelled veiling and background luminance as a measure of reduction in contrast due to disability glare. Case studies are reviewed where façade solar reflections flagged during early design as a traffic disability glare population dosage risk were successfully mitigated with façade treatments. Implications of façade solar reflectivity mitigation for building energy consumption are discussed.