Performance of Aged Asphalt Shingles and Development of Climate-Dependent Durability Index

Over 80% of the North American residential (steep-slope) roofs are covered with asphalt shingles. As the water-shedding layer, shingles are exposed to a wide range of weather elements. Weather shocks can negatively impact the field performance of a shingle. Existing North American standards do not provide specifications to quantify properties subjected to the weather shock aging process, and no protocol exists to determine the long-term durability of a shingle. To demonstrate the effects of field and laboratory aging and to develop a framework for the durability of shingles, the National Research Council of Canada undertook a long-term experimental program to evaluate the performance of fiberglass shingles from four different sources. The experimental program studied three aging processes: as-purchased, lab-conditioned, and field-aged. Over 325 specimens were evaluated while focusing on three key properties: tear strength, tensile strength, and fastener pull-through resistance. Properties of the as-purchased samples were used as a baseline to quantify the effect of aging on the shingles’ durability. This paper includes the statistical significance of the measured data. Nevertheless, for simplicity, mean values are used to derive observations and conclusions. Based on those data, the field-aged shingles displayed a maximum reduction of over 50% in tear strength. The majority of the evaluated properties after aging no longer met the minimum requirements that are specified by the North American standards that are referenced in the building codes. Based on these limited data, a framework for a climate-dependent durability index has been proposed for developing a performance-based classification. Demonstration of the framework uses measured mean values. The ongoing experimental program will expand the database and revise, if needed, the presented classifications with data that will be statistically significant.