Numerical investigation of radiant barrier roof systems using reflective and insulating layers for enhanced thermal performance in hot climates

This study numerically investigates the thermal performance of simplified multilayer roof assemblies for hot-climate applications. Six roof configurations were considered by combining aluminum or galvalume as the exposed upper reflective layer with polystyrene, polyethylene, or polyisocyanurate as the concealed middle layer and a rigid bottom substrate. A quasi-steady thermal analysis was performed in ANSYS Workbench 2020 R1 by applying time-varying solar-radiation and ambient temperature inputs as a sequence of independent quasi-steady-state calculations. The numerical model was checked using mesh-independence analysis and benchmarked against published experimental data. The results indicate that aluminum-based assemblies produced lower heat-flux transfer than galvalume-based assemblies due to the higher solar reflectance of the exposed aluminum layer. Among the tested configurations, combination-2, consisting of aluminum, polyethylene, and the rigid substrate, produced the lowest average heat flux among the aluminum-based cases, approximately 18 W/m². Combination-5, consisting of galvalume, polyethylene, and the rigid substrate, showed the lowest average heat flux among the galvalume-based cases, approximately 19 W/m². Since polyethylene was used as a concealed middle layer, its solar reflectance was not applied as an exposed-surface boundary condition; therefore, the observed performance should be interpreted in terms of the assigned material properties, layer arrangement, and simplified quasi-steady modeling assumptions. The findings provide a comparative assessment of selected multilayer roof assemblies and highlight the importance of exposed-surface reflectance and layer configuration in reducing roof heat gain in hot climates.