Roofs that resist one hail of a test storm

The first-ever indoor hail storm, recently staged in a cavernous laboratory by the Institute for Business and Home Safety, tested the hail resistance of various building materials. Approximately 10,000 one- to two-inch ice balls were fired from multi-barreled cannons onto a house and car in order to evaluate the performance of materials, including metal roofing (over solid sheathing and over shingles) and asphalt shingles (both traditional 3-tab and architectural). Details and results are as yet unavailable, as "researchers analyze the results." But from the myriad press videos, it's clear, at least, that aluminum gutters fair poorly. And according to one reporter who asked the right questions, the test confirmed what we would expect: Traditional 3-tab shingles suffered more damage than architectural shingles, and the portion of the standing-seam metal roof installed over solid sheathing fared better than the portion of metal roofing over asphalt shingles (to simulate a re-roof).

 

These results also confirmed what had previously been the most conclusive study of roofing performance in hail storms: The Hailstorm Investigation Program by the Roofing Industry Committee on Weather Issues, Inc. (RICOWI).This detailed study, prepared by seven inspection teams, examined more than one hundred roofing systems after a significant hailstorm, which passed through the Dallas/Fort Worth metropolitan area on May 24, 2011. Among the conclusions from the report:

• Hailstone size was more critical than hailstone quantity in determining if the roofing was damaged.
• IR-rated (impact resistant) asphalt shingle products performed better than standard asphalt shingles ... Standard asphalt shingles generally sustained moderate or severe damage when hailstone sizes were 1.25 inches in diameter or larger. IR-rated shingles generally performed well when struck with hailstones 1.75 inches or smaller.
• Materials that were unsupported, or installed over easily compressible substrates, had greater damage than those installed over solid substrates.
• Older roofing materials (10 years plus) sustained greater damage than new roofing materials.
• Hail effects on metal roof systems were seen as largely cosmetic (i.e. dents), rather than functional (tears that result in actual leaks). Even after impacts from the maximum hailstone size of 2.5 inches in diameter, no leakage was observed or reported.

Roofers in hail country may also benefit from a wealth of other information about roofing performance in hail storms. Examples include:

• To go deep on how to evaluate hail damage to ashpalt roof shingles, consult the Inspectapedia. (" We are not sure that hail will necessarily produce cracks or dents shown on the underside of asphalt roof shingles ... Cracks in my experience come with age, loss of volatiles, and shingles becoming dried and brittle.")
• For information of hail damage to flat concrete tile, this discussion from the The Inspector"s Journal Online is helpful. ("It can take up to a full year or longer for hail damage to show up on any roof covering ... The summer heat and then the winter freeze cycle is what really makes this type of hidden damage show.")
• The Tile Roofing Institute provides insights on distinguishing hail damage from manufacturing defects, and gives guidance on how to replace broken tiles, should your client suffer a severe hail storm. ("Take precautions not to allow excess adhesive to bond to the adjacent tile or create water blockage in the under lock.")
• Curious how rooftop photovoltaics perform in hailstorms? This industry report will help.  ("Laboratory statistics show very low failure rates for  this test [measuring failure from hail impact]")