How To Assess Hail Damage

Hail damage thresholds, what are they?

A hail-damage threshold indicates the smallest size of hail which might cause functional hail damage to a particular type of roofing.

Because a number of factors play a role in the causation of damage, a hail damage threshold is not a guarantee that hail of a certain size did or did not damage a particular roofing assembly.

Thresholds are merely rules of thumb that ballpark the opportunity for damage to occur.

Roofing System Threshold
Lightweight asphalt shingles
Heavyweight asphalt shingles and wood shingles
Medium wood shingles and clay tiles
Concrete tiles
Built-up roofing (smooth)
Modified bitumen membranes
1½” - 2”
EPDM membranes (smooth)
Other plastic singles-ply membranes (smooth)
1” - 2”
Membranes ballasted with gravel
Galvanized steel panels

How are damage thresholds determined?

Haag thresholds are the result of 52 years of impacting studies in the lab, as well as correlations of such research with many thousands of Haag field inspections. The table below lists established Haag thresholds for common roofing materials.

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