On May 24, 2011 several storms containing large hail passed just north of College Station, TX (Dallas/Fort Worth). According to the National Climatic Data Center, reports of hail 2 inches in diameter and larger were reported over the area. Large hail over 4 inches in diameter was also reported to damage airplanes and nearby airfields.
Trained inspection members identified affected roofs by properly identifying dents and other impact marks, known to be hail related. Property owners and other eye witnesses were interviewed to verify the extent of hail impact.
Trained inspection members identified affected roofs by properly identifying dents and other impact marks, known to be hail related. Proper data was then collected and analyzed. The data included metrics covering location, roof construction details, pitch, estimated hailstone size, and severity of hail impact. Impact severity was measured on a scale of 0 (no real damage) to 5 (severe damage and potential leaks as a result). y owners and other eye witnesses were interviewed to verify the extent of hail impact.
- Low Slope Roofing Systems
A focus of the investigation was to determine the differences between roofing products rated for impact resistance and those that were not. It was found that low slope roof systems that had membranes that were firmly supported by gravel or stone ballast performed the best.
- Asphalt Shingles
Asphalt shingles that were rated as impact resistant did perform better than those not. Out of the roofs that were tested 75% of the impact resistant roofs were rated in the damage categories 0, 1, or 2 (the lowest damage categories). The average damage rating for impact resistant roofs was 1.3. The damage rating for non-impact resistant roofs was 2.5. Older roofs also showed more damage than newer roofs within the same area due to additional wear and tear and aging.
Tile roofing systems performed well. Even though hail sizes were estimated to be between 2 and 4 inches, very few tiles had any damage. The damage noted on tiles is a pattern of multiple fractures from a single hailstone impact. Tile roofs older than 12 years also showed no noticeable differences in performance, probably due to lasting materials of clay and concrete.
- Metal Roofs
Most metal roofing systems also performed well. Of all of the metal roofs tested only 1 had severe damage where roof had distorted sides. None of the metal roofing systems, where raised, galvanized steel, or standing seam, had any evidence of leaks or punctures.
Hailstone damage was easily identifiable by the trained personnel on many varieties of roofing types. Hailstone size is more of an indicator of the extent of damage than hailstone number. Across the board impact resistant products performed better than standard products. Roofing systems that possessed a more substantial substrate also performed better than those without.
It appears that roofing systems that provide a complete system of protection from hail include impact resistant materials, a solid substrate backing, and a proper installation.