A comprehensive study conducted by Oak Ridge National Laboratory (ORNL) and the Cool Metal Roofing Coalition on the aged reflectance values for painted metal roofing and other roofing materials showed that solar reflectance and thermal emittance values of painted metal roofing degrade minimally over time.
According to the Coalition, several steps were involved in the exposure testing of painted polyvinylidene fluoride (PVDF) metal roofing. Solar reflectivity measurements were made quarterly at ORNL on steep and low slope metal roofs. After three years of exposure, white and bronze colored pre-painted PVDF metal roofing retained 95% of its original reflectance. In addition, panels of prepainted metal exposed at commercial weathering farms were tested for aged solar reflectance values. The same 95% retention of the initial solar reflectance and thermal emittance was seen again even after more than 30 years exposure in South Florida. The findings also indicate that this type of PVDF painted metal resists dust collection for at least 30 years. Data from the Coalition agrees with ORNL data, showing that emittance of painted metal actually increases slightly with time, but is not affected by differences in climate.
“We are very pleased with these dramatic, convincing results. While some roofing materials may claim better solar reflectivity properties initially, it is the long-term performance that has the greatest impact on cool roofing,” said Scott Kriner, Coalition chairman.
The Coalition works to educate architects, owners, specifiers and standards officials about the sustainable, energy related benefits of metal roofing. Its sustaining members include the National Coil Coating Association.