The Effect of Thermal Impact Factors on the Thermal Performance of Low-Slope Roofing Assemblies

Abstract

For decades materials of low thermal conductivity have been used to minimize heat flow through building systems. With advancements in sustainability and a demand for an increase in building envelope efficiency, there is a greater interest in the energy efficiency of insulating materials and their behavior in building assemblies. The heat flow in a low-slope roof system would be relatively simple to estimate if the insulation were continuous and the heat flow one-dimensional, but it becomes complex with the presence of gaps between insulation boards and thermal bridging. Over the past three decades there has been an increased focus on the problem of thermal drift in roofing insulation materials and thermal bridging. Thermal bridging is an inevitable mode of thermal loss in roof assemblies due to the use of mechanical fasteners to secure the roofing components. Similarly, thermal breaks due to gaps between insulation boards are anticipated due to installation and the dimensional stability of the boards. Currently, regulations and standards do not consider these thermal impact factors on the performance of roofing systems. As a result, proper analysis of these factors becomes more important as their relative influence on the thermal demand becomes more evident. The purpose of this research is to study these thermal impact factors and quantify their influence on low-slope roofing systems. The literature on this subject is in agreement that thermal losses resulting from these factors leads to drastic thermal inefficiencies; however, none of the studies provide general encompassing methods that may be applied to reach the building code design thermal values. This research considers an array of components and assemblies to provide generalized adjustment factors for the decrease in effective thermal resistance due to fasteners and gaps for the potential implementation in the energy codes.