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	1"
Heavyweight asphalt shingles and wood shingles	1¼”
Medium wood shingles and clay tiles	1½”
Concrete tiles	1¾”
Built-up roofing (smooth)	2”
Modified bitumen membranes	1½” - 2”
EPDM membranes (smooth)	2”
Other plastic singles-ply membranes (smooth)	1” - 2”
Membranes ballasted with gravel	2½”
Galvanized steel panels	2½”

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.