Frequency of hail is on the increase in North America, and causing significant damage to roofs, cars and other exposed surfaces. The southern and central areas of Alberta bear the byline ‘Hailstorm Alley’ for good reason, as many Calgary homeowners can attest.

Four Devastating Calgary Storms in 20 Years

1… The September 1991 hailstorm battered parts of the city with tennis-ball-size stones. This triggered 62,000 insurance claims totaling $342 million.

2… Then in July 2010 another Calgary storm produced stones measuring 1.5 inches across and resulting in $400 million’s worth of claims.

3… A further storm ravaged the city in June 2020. Some of the stones were the size of tennis balls falling at 100 k.p.h. The total bill came to $1.5 billion.

4… Scarcely a year passed before September 2021. The storm was milder although damage came to $247 million, and stones measured up to one inch across.

Of course, not all hailstones are that big in any storm. However, the spacing of those events, and the damage suggests many Calgary homes are risk.

Four Classes of Impact Resistance

There are four degrees of asphalt-shingle impact resistance. These are determined by Factory Mutual, and Underwriters Laboratories who may also test sample batches against them.

The following results per shingle makers IKO  show the relevant performance of these four classes in laboratories. Thus the tests do not reflect shingle temperature, age of shingles, roof slopes, and so on.

Underwriters Laboratory Standard Tests

• Class 1 shingles can withstand steel balls 1.25 inches in diameter.
• Class 2 shingles can withstand steel balls 1.5 inches in diameter.
• Class 3 shingles can withstand steel balls 1.75 inches in diameter.
• Class 4 shingles can withstand steel balls 2 inches in diameter.

Factory Mutual Standard Tests

• Class 1 shingles can withstand ice balls that are 1.25 inches in diameter.
• Class 2 shingles can withstand ice balls 1.5 inches in diameter.
• Class 3 shingles can withstand ice balls 1.75 inches in diameter.
• Class 4 shingles can withstand ice balls 2 inches in diameter.

What Happens When Hail Strikes Shingles

There are variables in these calculations as we mentioned. However, we can safely say that when a hailstone of sufficient size strikes an asphalt shingle with sufficient force, it can crack it and dislodge some granules. This makes the shingle more vulnerable to water intrusion, and other damage from UV rays, wind, and further hail damage.

This risk diminishes with high grade shingles.  Your choice depends on the risk you can afford to take, but do check with your insurance first because some insurers won’t cover for low grade shingles. Valiant Exteriors in Calgary phone (403)829-1661 may offer advice, but the decision rests with you, the homeowner.

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Hailstones Cause Severe Damage (Image FCB Excalibur BY CC 2.0)