The damage hail can inflict on buildings and property, particularly roof systems, has been an ongoing topic of concern to both property owners and the insurance industry for many years.  Sources report that damage from hail events in the U.S. approaches nearly $1 billion each year and appears to be increasing with time.  As a result, claims associated with hail-strike damage are one of the areas where forensic assessments frequently occur.

These claims are due in large part to the perceived relationship between a hailstorm that has recently passed through the area and any deficiencies or damage that has been discovered to a building envelope.  Hail can, and will, damage roofing materials.  A roof covering is considered to be functionally damaged by hail when the water-shedding capabilities decrease or its expected service life is reduced as a result.  Certain conditions must exist, however, for functional damage to occur.  These conditions must be accurately identified and analyzed through proper education, training, experience, and site inspection methodology.

The first and most important condition is determining the size of the hailstone.  Functional hail damage typically does not occur until hail reaches the threshold size for damage for a given roof material.  Without adequate size, the hail lacks sufficient mass and therefore kinetic energy at the moment of impact to cause damage.  Hail size can vary considerably from one location to the next and can best be conservatively determined based on measurements of damage to common readily visible metal surfaces at the site.

Other conditions relating to the likelihood for functional damage are associated with the perpendicularity of impact between the roof surface and the falling hailstone, namely the directionality of the oncoming storm and the roof, and factors which have decreased the impact resistance of the roof material.