Shingle Damage Evaluation – Size of the Hail Stones – Part 5b

Posted by in Shingles | July 16, 2012

This post is Part 5b of Shingle Damage Evaluation and follows Functional Hail Damage – Part 5a.

Considering the Size, Direction, and Damage Producing Effects of the Hail Stones 

The evaluation of composite asphalt shingles and other roof coverings for hail impact damage may be assisted by the determination of the size of the hail stones.  The size, direction, and damage producing effect of the hail can often be determined from an examination of other objects around the building and the other exterior building components.  Evidence of hail impacts include splash marks and/or indentations in light gauge metals, such as, roof vents, flashings, air conditioning fins, gutters, downspouts, siding, window sill wraps, screens, gutter covers or screens, window screens, etc.  The size, exposure, and severity of the splash marks (sometimes called spatter) and/or the indentations may give an indication of the size, direction, and damage producing effect of the hail.

Splash marks are areas where the discoloration from normal oxidation or dirt has been rubbed off the surface by the hail in a somewhat circular, usually tear drop shape.  Splash marks do not cause any functional damage, but may require the surface to be cleaned of the remaining discoloration so that the surface appears uniform in color again.  Industry studies estimate that the diameter of a hail stone that causes a splash mark was approximately 25% larger than the diameter of the splash mark.


splash marks in trim

SDE-32 Metal trim exhibits splash marks indicative of the size and direction of the hail stones.


splash mark in shingle

SDE-33 Splash mark on shingle indicates the size and direction of the hailstones.


Thin gauge metals are relatively easily dented by impacts from hail stones.  If thin gauge metals or screens are not dented, it is improbable that the shingles were exposed to a size of hail stone that could cause damage to a composite asphalt shingle.  However, indentations in these light gauge metals are not an indication that the shingles have been damaged by hail impacts.


dents from hail in metal flashing

SDE-34 Indentations in light gauge metal flashing from hail impact.


Wood surfaces may also be indented by  impacts from hail stones.  Some woods, especially weathered surfaces are relatively easily indented and/or cleaned of discoloration.  The splash marks in natural color wood surfaces, such as wood decks, will eventually discolor or may be concealed  immediately by lightly cleaning the surface.  Light indentations in naturally finished wood surfaces will become less visible as the wood material seasonally shrinks and swells.  Painted wood surfaces may require re-finishing or replacement. Indentations in the surfaces of the wood do not affect the function or service life of the wood.  The splash marks and the indentations are an appearance issue.


dent splash in wood deck

SDE-35 Composite wood deck exhibits splash marks and flattening of the roughened surface.


hail dents in wood trim

SDE-36 Paint fractures and indentations in wood trim from hail impacts


Weather reports, local news reports, and eyewitness reports are a somewhat unreliable source to determine the size of the hail stones.  It is human nature to perceive things to be larger than they are, especially when they are impacting against one’s own roof or siding.  These news and eyewitness reports usually provide an upper range in determining the size of the hail stones.  We have even found the professional hail tracking reports to be of limited use in determining the size of the hail stones: we have found them to be reliable in stating where hail did not occur, but limited in reliability in regard to the size and location of hail occurrences. Photographs and videos taken of the hail during and shortly after the storm are very helpful in determining the size of the hailstones, especially when other objects are included that provide a scale for estimating the size.


hail stones at nr

SDE-37 Hailstones measured in a North Royalton storm.


What Size Hail Stones Might Cause Damage to Asphalt Shingles?

Industry studies indicate that composite asphalt shingles can usually withstand impacts from hail up to ¾ inches in diameter without functional or cosmetic damage.  This is a lower bound, meaning that it is highly improbable that hail stones smaller than ¾ inches in diameter would cause functional damage to an asphalt shingle in reasonably good condition.  Some studies indicate that asphalt shingles can withstand impact from hail stones up to one inch in diameter without being functionally damaged.  In reality the size of damage producing hail may vary some due to the quality of the shingles, the condition or age of the shingles, the adequacy of the support directly under the shingles, the number of shingle layers, the hardness of the hail (such as, slushy ice versus solid ice), and the speed and direction of the wind driving the hail.  We have on occasion found no damage to asphalt shingles impacted by slushy hail stones greater than one inch in diameter.

In summary, determining the size, the direction, and the damaging effects of the hail stones on other building components assists in the evaluation of the shingles for hail impact damage by contributing much to the physical evidence found in the shingles themselves.  The next post will discuss some damages and anomalies that are often misunderstood for hail damage.