Tanya Brown-Giammanco & Anne Cope, Insurance Institute for Business and Home Safety
Field studies, including several post-hurricane assessments of asphalt shingle performance and numerous efforts to measure hailstone characteristics, have helped the Insurance Institute for Business and Home Safety (IBHS) shape its laboratory research program on asphalt shingles.
The core IBHS research facility is a specially designed, open-jet wind tunnel capable of subjecting full-scale, one-and-two-story structures to a variety of wind hazards. Small lab capabilities include a wind tunnel that can reproduce ASTM D 3161 and ASTM D 7158 wind tests and extend test wind speeds up to about 180 mpd for ASTM D 3161 and about 110 mph for ASTM D 7158. Additional capabilities include replicating UL 2218 and FM 4473 impact tests. Hail capabilities have expanded to include impacting specimens with lab-created realistic hailstones.
The IBHS asphalt shingle research programs seek to develop credible relationships between test standards, product ratings and real-world performance in wind and hail events.
Roof cover damage is a factor in a large number of disaster events and IBHS roofing research is focused on asphalt shingle performance because of their large residential market share. Recent post-disaster investigations conducted by IBHS following Hurricane Harvey found that more than half of the asphalt shingle roofs studied had roof cover damage, while this figure was more than 80 percent for Hurricane Michael. A closed-claims analysis of a 2011 hail event in Dallas-Ft. Worth showed that 90 percent of the property losses for homes studied had roof cover damage, and shingle roofs made up almost 80 percent of the dataset.
A wide variety of asphalt shingles now receives the highest ASTM D 7158 “H” wind rating, which pass at a basic wind speed of 150 mph. However, real-world hurricane performance has shown that shingle failures can occur well below 150 mph. Similarly, shingles that are UL 2218 or FM 4473 impact resistant have also been noted to sustain damage in real-world hailstorms, although to a lesser degree than standard shingles. It also is clear that wind and hail performance of asphalt shingles tends to decrease as they age.
Consequently, IBHS is investigating relationships between current test standards and product ratings during realistic wind events and hailstorms to allow for a reliable prediction of real-world performance and to help consumers choose more resilient products. IBHS has performed detailed measurements of steady and unsteady wind loads on shingles using ASTM D 3161 and ASTM D 7158 test protocols and compared resulting uplift forces with those from similar full-scale measurements in its core research facility. Researchers have tested many representative products using ASTM D 3161 and increased wind speeds to assess limits when shingles are well sealed. Research has also focused on the development of new test methods that uplift larger portions of shingles compared to ASTM D 7158 and a large dataset of samples is being accumulated.
UL 2218 steel ball drop tests have been replicated on 22 different asphalt shingle products ranging from commodity 3-tab shingles to premium and SBS polymer modified architectural shingles. A new hail impact test method was released in 2019, along with performance results for widely-sold basic impact-rated shingles, to provide a better connection to real-world performance. IBHS also has initiated aging studies where specimens will be exposed for 5, 10, 15 and 20 years to determine how their wind and hail performance changes. The first five-year samples were extracted in 2019 to undergo testing.
Twenty-two products, including many UL 2218 Class 4 impact-rated (IR) products, subjected to UL 2218 testing at IBHS did not perform well. In fact, none of the off-the-shelf products tested passed more than Class 2 impacts without at least one double impact location failing the UL 2218 performance criteria, despite the fact that the IR products tested were all rated Class 4.
General findings of the study included:
■ Architectural shingles generally performed the same as or slightly better than 3-tab shingles.
■ IR shingles performed better than their corresponding basic products.
Not all Class 4 rated products performed the same. There were brand-to-brand differences, and specifically, polymer-modified IR shingles as a group performed better than traditional IR shingles.
Crushed granules were often observed on shingle surfaces, which is not a realistic damage mode created by real-world hail.
The test method only considers cracking or tearing observed on the back of the shingle to be damage and does not account for things like granule loss or damage on the front side of the shingle, which have real-world performance implications.
Consumers deserve to have confidence that shingles labeled as impact resistant resiliently live up to their expectations. Thus, the IBHS Impact Resistance Test Protocol for Asphalt Shingles was born.
Since 2012, IBHS researchers have followed severe thunderstorms and collected hailstones to measure their mass, diameters and strength. These data provided a deeper understanding of the kinetic energy with which hailstones fall, their mass-to-diameter relationship and the strength of the hail itself, allowing IBHS to manufacture realistic hailstones back in the laboratory for testing.
Variations in strength and density led to the identification of three impact modes or types of impacts that occur when manufactured hailstones are launched at asphalt shingles. The hailstones may result in a “hard bounce” off the shingle, remaining nearly intact; a “hard shatter,” with the hailstone fracturing into numerous small pieces leaving no ice residue behind or a “soft” impact where the hailstone turns to “slush” on the surface of the shingle.
The IBHS Impact Resistance Test Protocol for Asphalt Shingles uses a hail cannon to launch 1.5-and-2-inch manufactured hailstones at roofing test panels built with shingles purchased from distribution.
The IBHS Test Protocol differentiates the performance of widely-sold IR shingles currently on the market by replicating the properties of natural hailstones and providing a quantitative evaluation of performance. Moving beyond pass/fail testing provides more detailed performance information for consumers looking to purchase a better performing product, roofers looking to sell a better product and manufacturers who wish to improve their products.
At this point in the IBHS research program, it is clear that
wind uplift forces on shingles do not depend directly on roof surface pressures. Loss of shingles during strong wind events is as likely to originate in the middle of the roof as along the edges or in the corners where roof uplift pressures are greatest. However, ASTM D 3161 and ASTM D 7158 produce steady uplift forces as compared with those exerted by turbulent winds that engulf a building during strong winds. The turbulent winds and wind structure interaction produce higher short duration uplift forces for a given gust wind speed at mean roof height than those produced by ASTM test standards running at a constant speed equal to the gust wind speed. For tests conducted at the same wind speed, ASTM D 3161 produces higher uplift forces on shingles than ASTM D 7158.
For most shingle products, the key to wind performance is how well the shingles seal to the courses below and how well that seal is maintained over time when exposed to the elements. Preliminary observations from the recently extracted IBHS-aged samples indicate that for some shingles, the seal may be stronger after five years of exposure, while for other shingles, the strength has deteriorated over time. There are some indications that increased toughness and flexibility of polymer-modified shingles may allow them to survive a storm even if the seal is broken. Tougher shingles might reduce the number of re-roofs needed after a major storm. It would also be a huge win if water doesn’t get into a building when shingles lose their seal and begin to lift, which is why IBHS’s FORTIFIED Roof designation requires a sealed roof deck.
IBHS is an insurance industry supported non-profit that conducts objective scientific research to identify and promote effective actions that strengthen homes, businesses and communities against natural hazards and other causes of loss. Brown-Giammanco is IBHS Managing Director of Research. Cope is IBHS Chief
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