Effect of Surface Mass on Roof Thermal Performance

Abstract

The roof of a building is exposed to the most severe environment that is experienced by any component of a building envelope. Diurnal peak surface temperatures of 140 to 185 °F are not uncommon. The addition of thermal mass to the exterior surface of the roof should lessen the severity of the environment that is experienced by the roof membrane and the roof insulation. The exterior mass should result in attenuation both of temperature extremes and of heat flux variations. It also may result in lowered net heat flow through the roof. This paper presents some results of a combined experimental and analytical study to quantify the effects of surface mass. Measurements were made on roof test panels that were exposed to the weather of eastern Tennessee. The test panels consisted of glass fiber insulation with a modified bitumen membrane. Experiments were conducted on a bare panel and on a panels that were loaded with either concrete pavers or aggregates. A heat transfer model for the bare panel and the panel with concrete pavers was developed to calculate the internal temperatures and heat fluxes using measured indoor and ambient conditions. The model was validated by comparing its predictions with measured values. Following validation, the model was used to perform a parametric study of the effects of various levels of surface mass.