Thermal Roof Insulation in Tropical Buildings

Abstract

Model huts were constructed for tropical studies of the heat penetration of painted and unpainted galvanised steel roofs in combination with various commercial under-roof insulations. The results showed that a white painted roof and unpainted roofs with various insulations had similar resistances to heat penetration, but the white roof case allowed interior heat to escape faster and thus was superior for thermal comfort purposes. However, a combination of white paintedness and under-roof insulation was much better than either measure alone for overall insulating performance. It was concluded that dust buildup on upward facing, reflective under-roof insulating surfaces degrades their performance significantly compared to other cases. Measurements were made of the relative emittance and absorptance of weathered and unweathered steel roofs. The quotient of these surface optical properties was found to correlate with the heat penetration and thus provides a means of evaluating heat penetration of old roofs by in situ measurement of these properties. It is predicted that moderate weathering will have little effect on the heat penetration of white painted or unpainted galvanised steel roofs.