Roofing folklore

Physics can disprove an urban legend about moisture accumulation in highly reflective roof membranes

For quite some time, the roofing industry has been using highly reflective low-slope roof membranes—commonly referred to as "cool roofs." From their early uses in the 1990s, these cool roofs have been said to cause moisture accumulation in low-slope roof systems throughout the U.S. in hot and cold climates. These statements have come from all contingents in the roofing industry and slowly turned into an urban legend.

This urban legend says an owner or designer should avoid a cool roof because it will accumulate more moisture underneath it when compared with nonreflective membranes. Once the thought of moisture accumulation under a roof membrane is in place, the fears such as facer failure, loss of R-value and biological growth follow.

This type of information currently is being used in marketing materials for noncool roof membranes and presented in sales presentations as fact with little to no science or facts to substantiate the claim. However, when physics are used to evaluate moisture accumulation in highly reflective roofs, this roofing industry urban legend can be disproved.

Temperature differential