DisasterSafety.org

Summary of State Hail Maps

Hailstorms are a major cause of loss for our member insurance companies. Every time there is a significant hailstorm in the Midwest, our members pay out millions – and sometimes billions – of dollars due to damages roofs, siding, etc.

For the past few years, IBHS has been encouraging the use of roofing products that achieve a UL 2218 Class 4 rating. This means that samples of the roofing materials have to withstand two impacts from a two-inch steel ball dropped from 20 feet without damage to pass. Claims studies have shown that policies on homes roofed with shingles meeting this test standard are significantly less likely to have a claim after being subjected to a hailstorm.

Recent efforts in the model building code arena have focused on developing impact-resistant roofing requirements for those areas subject to frequent occurrence of extreme hail. For example, NFPA 5000 Building Construction and Safety Code identifies the areas shown in the map below as having substantial frequency of large hail. Specifically, the map shows areas that should expect to see 1.5” or 2.0” hail at least once every 20 years.

This map was developed through statistical analysis of hail reported by the National Severe Storm Laboratory from the early 1950’s to the late 1990’s by using a software program called CHAP that was developed by Haag Engineering in Dallas, TX.

Recently, the IBHS Engineering Department has used this software to dig a little deeper. Instead of focusing only on extremely large hail, we have looked into the occurrence rate of damaging hail. We have defined “damaging hail” as any reported hail that is larger than 0.75” in diameter. This threshold was chosen because this is the commonly accepted size where damage to asphalt shingles is expected by the majority of hail experts in the country.

The following maps breakdown the expected number of times in 20 years (assumed average life of a residential roof) that damaging hail will fall within individual counties in Great Plains, Midwestern and Southwestern states. It should be noted that the occurrence rates of damaging hail are substantially higher than those of the extreme hail noted above. For example, counties of Northern Texas and Southern Oklahoma can expect damaging hail to occur upward of 12-14 times every 20 years.

Click to enlarge: