Preliminary Exploration into the Effects of Metal Roofing on Solar Heat Gain

Metal roofing panels and tiles have been proposed as an alternative to traditional asphalt shingle roofs. Benefits over asphalt shingles include a service life that is two to four times longer and improved recyclability.  In this project, the improvement in energy efficiency due to decreased summer cooling costs was investigated.  Methods included analysis and simulation of the modes of heat transfer by radiation, conduction, and convection.  Heat input from radiation was characterized for typical roof geometries as a function of latitude, longitude, and time of day.  Small scale, portable physical models representing roof decks and attics were constructed and used for data collection on several clear sunny days during July and August, 2015.  Preliminary results verified that attic temperatures were reduced when a model with metal roofing panels was compared to an identical control model with asphalt shingles.  Although the lower absorptivity of the metal roofing was a principal factor, heat transfer analysis also indicated that the lower thermal capacitance of the metal roofing resulted in a significant decrease in the amount of energy storage within the roof structure itself.  Data analysis is ongoing with a goal of designing a quantitative model for predicting energy savings.