The Comparative Effect of Four Reflective Coatings on the Thermal Performance of Residential Roofing in Climate Zone 8B

Roofs serve as a crucial interface between the earth’s atmosphere and its human-made environments. They contribute up to 60% of the total cooling load in any building and comprise close to 25% of the surface area of any city. With temperatures at their highest since first recorded in 1850, energy-conscious roofing design is paramount. This study compared the internal temperatures of five houses, each with a different roof coating, in order to expand understanding of the relationship between roof reflectivity and internal thermal comfort. It was hypothesized that the houses with roofs of a higher reflectivity would have a lower internal temperature because less solar energy would be absorbed. Five 30.40 cm square houses with pitched roofs, covered individually in black shingles, ultrawhite paint, or ultrawhite paint plus an additive, were placed in a zero-shade outdoor space in U.S. climate zone 8B. The internal temperature of each house was taken twice daily for 22 days in October. Results showed that the shingled roof, with low reflectivity, had the highest temperature difference (M=0.76, SD=0.66) from the mean, while the reflective ultrawhite roof experienced temperatures 1.11°C cooler than the shingled roof. These findings, paired with results of an ANOVA test with an alpha value of less than 0.05, suggest there were significant differences between groups. The implication of the study’s findings is that black shingles should be replaced with roofs of higher reflectivity and a promising alternative is readily available white paint.