Hail Damage Standards – Part 3


In the continuation of the series on Hail Damage Standards, we will now focus on defining Functional vs Cosmetic” hail damage to shingle roofing and other building components.  As discussed before, our goal in this blog series is to accurately and consistently determine hail damage to roofing and building components.

In this series on hail damage, we have previously discussed the characteristics of hailstones and the velocity and directionality characteristics of hailstones.  The final blog will discuss the appropriate inspection procedures.

Definition of Hail Damage – “Functional vs Cosmetic”
For insurance purposes, hail damage to roofing-covering materials is defined as either “functional” damage or “cosmetic” damage.

In general terms, “Functional damage” is damage which diminishes the ability of a roof to shed water and/or reduces the roof’s expected long-term service life.

Cosmetic Damage is damage which doesn’t meet the definition of “functional” and therefore is considered “cosmetic.”  Cosmetic issues may include discoloration or damage which doesn’t affect the lifespan of the roofing material or reduce its ability to shed water.  Cosmetic damage is that which only affects the appearance of a material, or affects its functionality to only a minor degree.

Hail damage to asphalt shingles is observed as fractures (bruises) in the shingle mats and also as punctures and tears to the exposed shingle tabs.

Hail impact marks are classified into two categories: functionally damaging impact marks and cosmetic impact marks. Functional impact marks occur when the shingle mat is bruised or fractured. Cosmetic impact marks occur when the granular surface of the exposed shingle tab is “scuffed”, leaving the underlying asphalt and mat physically undamaged. Granule loss is not considered functional damage. Functional impact damage becomes more prevalent when hail size begins to approach 1-inch or more in diameter.  It has been shown through many field observations that hail impact-caused fractures only occur in new shingles with hailstones in a range from 1¼ inches to 2¼ inches in diameter (depending on shingle product, support conditions and local environment).

The exposed asphalt on recently bruised or fractured shingles will visually appear black in color. Asphalt that is exposed to the environment for several months will turn grey in color as it oxidizes and forms a grey surface film. The amount of damage will also be affected by the part of the roofing material that’s hit. The edges of roof components, such as wood and asphalt shingles, are more fragile and subject to damage than material in the middle of the components, since the edges have less surrounding material for support. Ridge and hip cap shingles are poorly supported, so they are more likely to suffer hail damage.

Characteristics of Damage
The effects of hail strikes on asphalt shingles vary according to the conditions at the time of the hailstorm. If hail is accompanied by rain, as is common in the U.S. in the Midwest and on the East Coast, the rain will cool the roof, making the asphalt harder.  Hailstones striking rain-cooled, hard asphalt are more likely to loosen or displace granules.  On the West Coast, hail may not be accompanied by rain, so roofs may be hot and the asphalt may be soft when the hailstones hit.  Hailstones striking hot, dry, softer asphalt are more likely to embed the granules deeper into the asphalt.  This means that conditions during the hailstorm can influence the appearance of hail damage.

When the hailstone strikes, the shingle flexes downward. The top surface of the shingle is in vertical compression and the bottom is in horizontal tension.  The bottom surface of the shingle has to expand in order to absorb the impact of the hailstone. This expansion creates tension, which is relieved by cracking and is often confused with “blistering”, a common phenomenon with poor quality or older shingles. This cracking is referred to as a fracture.

A shingle fracture starts at the bottom surface of the shingle and spreads toward the top surface. If the stress is great enough, the shingle will fracture clear through, from bottom to top. If the fracture extends through the mat, the shingle has suffered functional damage.

The hail strike may not be severe enough to cause a fracture extending clear through the shingle. The fracture may extend through the mat but not reach the upper surface. This condition is called a bruise because it creates a soft spot on the shingle, which you can feel with your finger. It feels like the bruise on an apple.  Bruises are functional damage.

Although the mat is only about 2% of the shingle’s weight, it is a crucial component in determining the impact resistance of asphalt shingles.  Thicker, heavier mats resist damage from impact more effectively than thinner ones. Mat thickness varies among manufacturers and among shingle types produced by the same manufacturer.  Again, a fractured mat is functional damage.

Asphalt Composition
Asphalt used for asphalt shingles varies in both quality and thickness, and these two properties can affect the severity of hail damage.  Poor-quality asphalt can be the result of poor-quality or improper ingredients used to manufacture the asphalt, or the ingredients may be used in the wrong proportions. Quality is also affected by the manufacturing methods.

Asphalt used in the manufacture of shingles may be blended by a shingle manufacturer or bought already blended from a supplier. The methods for mixing asphalt are proprietary and manufacturers do not publish this information. During an inspection, there’s no way to judge the quality of asphalt; just know that the quality can vary.

The thickness of the asphalt that is applied to the mat varies among shingles produced by different manufacturers. Obviously, a thicker asphalt layer (typical in an “architectural laminated series” shingle) resists fracture more effectively than a shingle with thinner asphalt (typical of 3-tab shingle) of similar properties.

A crack in the asphalt layer does not constitute functional damage. The crack must extend through the mat to be functional damage.

Damage to the Granule Layer
Generally, granule loss is NOT considered to be functional damage.

A few missing granules do not constitute functional damage. Excessive and recent granule loss has to be readily visible to the roof observer to qualify as functional damage.  If the observer has to bend down and squint to determine whether or not it is a hail strike, then granule loss is not severe enough to qualify as functional damage.

Hail damage to the granule layer is affected by a number of variables, including the properties of the shingles, the properties of the hailstones, whether the hail is wind-driven, and the orientation of the roof plane to the direction of hail fall.  The ways that these variables combine affect the nature of the granule loss.

The amount of granule loss caused by a hail strike is affected by the amount of impact-energy carried by the hailstone. The amount of damage done to the granule layer is related to the hail’s properties, such as size, density, and free-fall velocity.  Wind-driven hail carries more impact-energy, so it may cause more granule loss on older roofs.

The condition of a shingle roof affects the amount of damage that hail will inflict.  As shingles age and deteriorate, they become increasingly brittle and less able to absorb the impact of a hail strike. Older shingles are damaged more easily than newer shingles.  On older shingle roofs, many granules may be loose but still in place. These loose granules can be dislodged even by small hail. This is not considered hail damage because the granules were already loosened.

Shingle quality is also a consideration. Given hail with identical impact-energy, thin, low-quality shingles (3-tab) will suffer damage before thick, high-quality shingles (architectural laminated).

In the final blog in this series on hail damage, we will look at the appropriate inspection procedures for shingle roofs.

Founded in 1997, The Warren Group, forensic engineers and consultants provides technical investigations and analysis of personal injury and property claims as well as expert testimony for insurance adjusters and attorneys. Extremely well versed in the disciplines of mechanical, electrical, chemical, structural, accident reconstruction and fire and explosion investigation, our engineers and consultants are known for delivering the truth — origin, cause, responsibility and cost of an event or claim — with unmistakable clarity.

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