1 Aging and Hail Research of PVC Membranes Frank J. Foley, Jim ...

For 1997 (the only year posted on the web site), the mean monthly UV index for Arizonacalculates to 6.25 while the mean index for Minnesota is 3.25. Within the total averageof all 13 states in this study (Item b in Table 3) roofs in Arizona were aged an additional32.7%, while roofs in Minnesota were made 30.9% younger.Arizona WeightingMinnesota Weighting(6.25 – 4.71) / 4.71 = + 32.7% (3.25 – 4.71) / 4.71 = - 30.9 %Thus, the age of all roof samples taken from Arizona increased by 32.7%, and the ageof Minnesota samples were reduced by 30.9%. Going forward, test results thatreference “UV age” or “UV factored age” are a result of this method of factoring.This crude method of UV factoring makes the assumption that a month's aging processfor a July Arizona roof is 10 times faster than a January Minnesota roof. No empiricalsupport for this consideration exists. Consistent observations of sun and heat exposureare the two primary weathering agents of PVC roof aging. Southern U.S. PVC roofsage more rapidly than northern roofs. Regardless, as depicted in the next table, this“factoring” bias among the samples is fairly uniform in impact. Understandably the roofsamples among the four manufacturing groups were evenly dispersed, both in age andgeography.Aging by Manufacturing GroupsTable 4 reports four distinct manufacturing groups (group identification here is A, B, C,& D) were sampled with mean age and mean UV-factored age.GroupIDNo. ofSamplesMean Ageof Samples(Years)FactoredUV Age(Years)DIFF %A 20 5.79 6.08 0.29 5.01%B 21 4.30 4.74 0.44 10.23%C 25 4.95 5.42 0.47 9.49%D 21 5.83 6.05 0.22 3.77%87Table 4: Four manufacturing groups, mean and UV factored ageNotably, the newest of the four manufacturing groups was Group B with an average ageof 4.3 years. This group had the greatest amount of UV factoring - an additional .44years (about 5 months). If a false-positive bias in aging exists due to the factoringmethod (if a July Arizona roof does not age faster), then Group B will receive thegreatest percentage of false bias. In contrast, the oldest of the four groups (group Dmean exposure of 5.83 years) received the least amount of factoring - an additional .22years (about 2-1/2months).8