Wind Uplift Resistance of Artificially and Naturally Aged Asphalt Shingles

Damage assessment surveys performed following the 2004 and 2008 hurricane seasons indicate that the vulnerability of shingle roofs to wind-induced damage increases with age. This paper presents two interrelated experiments on the wind uplift resistance of asphalt shingle seals. The objective is to identify whether and to what extent aging reduces the wind uplift capacity. In the first experiment, asphalt shingles were artificially aged, and the mechanical uplift resistance was measured at discrete intervals. In the second experiment, mechanical uplift tests were performed in situ on $\ge 9\text{-year-old}$ shingle roofs installed on four central Florida homes. Results from the first experiment demonstrate that heat exposure can reduce uplift resistance along its sealant strip in some products; however, the excess capacity in the bond may be sufficiently large to prevent the mechanical resistance from dropping below the design requirement. Inclusion of ultraviolet and water in the heat-exposure tests did not appreciably change these outcomes. Results from the second experiment, which assessed in-service roofs on single-family homes, support this finding. Overall, the results suggest that aging of the sealant strip may play a secondary role in increasing the vulnerability of shingle roof systems to wind over time. Results from a companion project performed concurrently to this one strongly demonstrated that progressive unsealing (not loss of strength) is a culprit. Improving shingle design to prevent or halt unsealing, without degrading the capacity of the sealant, appears to be the most promising solution to reducing roof cover damage.