Background

The sun radiates heat energy and raises roof temperature as much as 70 degrees above ambient temperatures. This temperature rise seals heat in attic systemos and increases cooling costs. Reflecting solar heat back out, emitting heat radiation, and transfering convective heat are ways roof materials can stay cool. Adding attic ventilation to improve roof convective transfer and thermal insulation to prevent solar heat from penetrating building ceiling can further improve energy efficiency and durability of roof systems. Energy efficiency has to come with durability to last for decades and low mainatenace cost against weather and elements. Factors which can shorten the lifetime of a roof include ultraviolet radiation from the sun, freeze-thaw cycles, wind, rain, damage from foot traffic, biological growth, chemical reactions with air pollutants, thermal expansion stresses due to temperature changes, and poor installation. Thus, if a cooler material is inferior from a cost or lifetime point of view compared to a warmer material, it's not a good deal.

Below is a temperature rise ranking of materials and coatings based on their solar reflectivity. See how A black opaque surface in the sun can become up to 70°F (40°C) hotter than the most reflective white surface. High solar reflectivity and high thermal radiation emissivity help reduce heat up to about 1/5 as mich as black materials above air temperature.