The use of highly reflective roof membrane systems is being promoted and in some cases required in energy codes and green building codes and standards. Highly reflective membranes, which typically are light in color, have demonstrated reduced overall energy consumption in cooling dominated climate. These membranes also are theorized to reduce the heat island effect. Concern has been expressed about using highly reflective roof membrane systems in cool to cold climate zones because they potentially increase moisture accumulation in roof systems. Roof membranes are vapor retarders. The theory is that highly reflective membranes reflect a percentage of the heat that could enter the roof assembly, potentially providing a condensing surface on the cold side of the roof assembly during winter months. The other concern is that roof systems using highly reflective membranes will not get hot enough during the summer months to dry out moisture that may have condensed or otherwise entered the roof assembly. This study focuses on mechanically-attached, highly reflective, single-ply roof systems installed on low-slope (less than 2:12) structures in cool to cold climate zones. Three sources of data are considered when determining the moisture accumulation potential of these systems.
1. Test roof cuts taken during the winter months
2. Modeling data from a building envelope model specifically designed to evaluate
moisture accumulation
3. Data from previous studies to determine the effects of roof membrane color on the
drying rate of low-slope roof assemblies