Ask An Expert: Hail Damage to Residential Roofs

Ask An Expert is a question-and-answer column designed to address common questions related to forensic investigation and property damage. Each month we’ll feature one or two questions submitted by you – our readers and customers – and provide detailed, easy-to-understand answers. Email your questions to [email protected] or submit your questions here.

Can you give a brief overview of hail damage to residential roofs? What other resources are available?

John Miller, P.E.: Hail damage to roofing materials is defined as an identifiable mark caused by hail that has measurably reduced the integrity or functionality of the overall material, where the material was sound prior to the hail impact.  Residential roofs are covered by a variety of materials, including asphalt shingles, metal, concrete and clay tiles, and fiber-cement tiles; however, four out of five houses in the United States are covered with asphalt shingles.  Over 12.5 billion square feet of asphalt shingle products are manufactured annually.  Hail damage to asphalt shingles is most often found as a bruise (deflection) that extends through the entire thickness of the shingle.  Hailstones can cause a complete fracture (penetration) in a shingle.

Hail damage to asphalt shingles is visible to the naked eye.  The bruises or fractures are typically circular and close to the same size as the hailstones.  Therefore, if it takes 1-inch-diameter hail or larger to damage an asphalt shingle, then the bruise or fracture should be close to 1 inch wide or larger.  A classic hail bruise removes granules around the outer edge of the bruise while leaving granules in place in the center.  Hail impacts that have damaged the fiberglass mat will typically leave an indentation on the backside of the shingle.

Before determining whether the roof covering is hail damaged, a search for collateral indicators of hail impact should be made on the property.  Collateral indicators are very important in determining the size and density of hail that fell at the property.  Collateral indicators include exterior wood and metal surfaces, window cladding and screens, and air conditioner condenser fins.  Hail large enough to damage shingles will typically leave clean spots, dents, and tears in these materials.

When examining the shingles, the most susceptible shingles should be studied first.  Inherently susceptible shingles are those that would have faced the incoming hailstones, and those that are less firmly supported from underneath by a rigid roof deck.  Shingles that cover ridges, valleys, shingle edges overhanging eaves and rakes, and the edges of shingles themselves are inherently more susceptible to hail damage due to the absence of firm backing.  If hail damage is found on the field shingles, you should find hail damage on these more vulnerable shingles.  The field shingles should then be examined, looking for circular bruises or fractures with associated granule loss that is consistent with hail impact in size and shape.  When possible, examine the backside of the shingles for indentations.

Resources for information on hail damage to roofing materials can be obtained from Donan’s website, in the search bar at the top-right corner of the page; the Roofing Industry Committee on Weather Issues, Inc. (RICOWI),; Jim D. Koontz & Associates, Inc.,; and other online sources.

You can also learn more by attending an upcoming webinar or viewing other resources at

About the Expert
John Miller joined Donan in 2009 and currently serves as a forensic engineer and principal consultant based out of the firm’s Louisville, Kentucky office. His area of expertise is structural engineering with an emphasis on structural damage from impact, wind and flood. Mr. Miller’s project capabilities also include a wide range of civil and structural investigations including hail damage, foundation damage and water intrusion.  View John Miller’s full professional profile here.

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