What are Hail Ratings (Impact Resistance Ratings)?

More roofing definitions

Underwriters Laboratories Inc (UL), an independent, for-profit company, has developed a series of laboratory test to measure how well roofing materials resist hail. These tests are widely accepted by the roofing industry, and the results are widely quoted in industry promotional materials.

UL standard 2218 describes a series of tests which involve dropping steel balls from various heights onto roofing materials, and then measuring whether the material cracks. The roofing materials that show the greatest resistance earn a Class 4 rating. Those with the least resistance earn a Class 1 rating.

Note, however, a few caveats:

1. Manufacturers report their hail ratings voluntarily -- thus you may not find hail ratings for shingles that don't perform well.
2. While metal roofs are unlikely to crack during a hail storm, they may become permanently dented, and the hail ratings do not take this into account.
3. Hail resistance tends to degrade over time with most roofing materials.

While hail can be a significant problem in some areas, few building codes require the use of impact resistant roofs. If you're thinking about putting new shingles on your roof, call your home insurance company -- they may give you a discount on your insurance policy if you install impact resistant shingles.