Cool roofing coatings. Considerations in formulating and using: Fid-Bau Portal

Cool roofing coatings. Considerations in formulating and using

Torres, Jorge / Connolly, J.D. / Bustos, Daniel / Burgos, Gabriela

White, cool roofing coatings are associated with reduced heat build-up of roofing surfaces and are directly correlated to the lowering of utility bills associated with the cooling costs for the buildings which utilize them. White coloration, however, is not the only criterion to use in judging whether a cool roofing coating will be effective. An efficient cool roof is a system combining the coating formulation and the underlying substrate, exposed to the elements. Using measurement of solar reflectivity and resulting heat build-up (temperature rise), the effect of TiO₂ grade, extender content, substrate type, and dirt condition of the paint film surface is discussed in terms of its ability to retard temperature build-up. This article shows that there is a close relationship between TiO₂ content in a roofing formulation and its solar reflectivity value. Increasing a roof coatings' reflectivity value results in a positive effect on temperature reduction, thus improving environmental benefits due to a reduced need for air conditioning systems, as well as a reduction in the heat island effect in urban areas. Furthermore, it was demonstrated that the quality of TiO₂ used in high reflective coatings formulations directly affects the reflectivity and temperature reduction values. In addition, temperature reduction in a roof system depends not just on the coating, but also on the substrate used. A better cooling performance was observed with metallic substrates, such as galvanized steel roofs and aluminum panels. Good temperature reduction was also noted with PVC, bricks (red and cinder), and polycarbonate roofs. However, poor performance was observed with red clay tiles. Finally, it was shown that after a dusting process, white coatings applied over real substrates change their cooling properties, offering a dramatic increase in temperature as reflectivity drops.