Exposure, measured in the rate of solar radiation received per unit of area, is called insolation. It is typically expressed as watts per square meter. Under very clear skies, up to 1220 Watts per square meter reaches a rooftop — an amount equal to an array of household hair dryers every ten feet on a roof, according to the Roof Coatings Manufacturers Association.
With the potential for roof temperatures to rise 90 degrees Fahrenheit above the ambient air temperature, high temperatures shorten the life of commercial roofing systems made of organic materials. The rate of degradation also begins to accelerate at elevated temperatures, RCMA says.
“Most people apprentice that white coatings result in savings on cooling costs, but enhanced roof longevity, especially in northern states, can be another major benefit that could result in at least as much savings,” says Thomas Meyer, co-chairman of the White Coatings Council.
A rule of thumb for thermal aging is that service life is cut in half for every 18 degree Fahrenheit increase in temperature, RCMA says.
