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Residential roof assessments: a guide to evaluating damage to asphalt composition shingles.

Damage assessment of residential roofing is typically a hot topic after a major storm passes through a neighborhood, particularly after large hail events and strong wind events. Strong wind events may cause portions of roof coverings to tear away, which may be easily recognized from the casual observer walking through the neighborhood.

Damage from hail or minor wind events, on the other hand, is typically not apparent from grade. Consequently, many claims are filed by homeowners who are uncertain of the existence or extent of damage from a storm event. Sometimes, homeowners are frustrated by apparent inconsistencies in the assessment of their roofs by various parties--such as roofing contractors, insurance adjusters, independent engineers, and friends--after a storm. Homeowners may be confused or upset as to why some roofs in a neighborhood require complete replacement, while their own roofs have little or no damage. Other homeowners may be confused as to why their gutters and downspouts have obvious indentations from hail impact, yet their roofs have no damage.

Because of this, it is helpful to have a basic understanding and general overview of residential roofing assessment. The following information will help claim professionals evaluate reported storm damage, and will focus strictly on asphalt composition shingles. Information in this article is based upon a technical paper published by the American Society of Civil Engineers (Forensic Engineering 2009--Pathology of the Built Environment--Proceedings of the Fifth Congress on Forensic Engineering) and presented in Washington, D.C. in November 2009. The paper was written and presented by engineers from Rimkus Consulting Group, Inc. (Luke M. Sharara, P.E., James W. Jordan, P.E., S.E., and Ross A. Kimble, P.E.)

Hail Damage Assessment

It is important to understand a few key characteristics of hail. Hailstorms produce hail that is not of uniform size, shape, or density (Figure 1). In addition, hailstorms may vary in intensity across a short distance.

This randomness, combined with numerous variations in individual roof coverings, necessitates detailed and independent evaluation of each subject roof covering. The variation in roof coverings and the randomness of hail within a particular storm often results in varied degrees of damage within the same neighborhood, including instances in which damage may be found on one house but no others in a neighborhood.


Roof covering manufacturers test their materials to determine resistance to hail impacts in accordance with published standards. One of the most common standards, UL 2218 "Impact Resistance of Prepared Roof Coverings," is produced by Underwriters Laboratory, which groups roof coverings into four classes: Class I to Class IV. (Class I is the least hail resistant, while Class IV is the most resistant.) Other technical organizations involved with roofing materials include: American Society of Testing and Materials (ASTM), Factory Mutual Research Corporation (FMRC), and the National Institute of Science and Technology (NIST). These standards provide important guidance in evaluating roof coverings and determining susceptibility to hail impacts.

As would be expected, hail impacts to asphalt composition shingles can damage shingles with varying degrees of severity. When assessing hail impact damage to asphalt shingle roofs, claim professionals must determine or define the term "damage." A generally accepted definition of such damage is "the loss of watershedding capability or a reduction in the expected long-term life of the roofing material." This is a functional definition that has industry acceptance, and consists of two components, either of which may indicate a specific location as damaged.

The first component is the loss of water-shedding capability. Large hail may immediately puncture or tear shingles, resulting in a potential leak.

The second portion of the definition is the reduction in the expected long-term life of the roof covering. Asphalt shingles have a granular coating that serves both functional and aesthetic purposes. Functionally, the coating provides a wearing surface for the roof.

The granular coating also protects the underlying asphalt-impregnated base mat from the sunlight's ultraviolet rays as well as from mechanical abrasions, such as that from foot traffic and other forms of incidental contact. When this granular coating wears off or is removed, the underlying asphalt base mat becomes exposed and is more susceptible to mechanical damage and will experience accelerated degradation due to ultraviolet rays. This accelerated degradation may result in a reduced service life in the area of granule loss and therefore might meet the criteria of damage, depending on the severity.

Hail impacts may produce randomly located areas of damage that are round and localized. Damage severity increases with greater hailstone sizes. Severe damage typically consists of bruising (localized softness due to material fracture) or physical tearing of the shingle base mat. See Figure 2 for examples.


False Positives

Because one of the characteristics of hail damage is granule loss, some controversy arises from granule loss caused by other conditions. The most common of these conditions are weathering, blistering, scuffing, marring, flaking, and mechanical damage.

Weathering or aging of the shingles typically manifests itself as broad, irregularly shaped granule loss that exposes the underlying asphalt impregnated base mat. Weathering will affect large areas of the shingle and the roof, and will typically be more pronounced on slopes exposed to direct sunlight and on roof coverings with inadequate or reduced ventilation.

Blistering is a condition that occurs when gas pockets from within the base mat rise to its surface and release the air within them, displacing a few granules. See Figure 3 for example views of blistering. The size of these individual blisters is typically smaller than what is caused by hail impacts. Blistering also occurs more often on areas of roofs with inadequate ventilation.


Scuffing is caused by abrasive forces pressed against the shingle surface, most notably due to foot traffic. As a result, scuffing is often found in areas where people have a tendency to walk, such as valleys or slopes that lead from upper to lower roofs.

Marring occurs when forces push or shift (without removal) portions of the granule coating and the top surface of the base mat. This typically occurs when the roof covering is hot, and often occurs due to foot traffic, as well.

Flaking is characterized by the loss of small groups of granules that are not adequately adhered to the base mat. Algae growth is sometimes mistaken as hail damage. Often walking upon or application of light finger pressure to areas that are flaking will cause the loss of additional groups of granules. Because of the brittle condition of the granule coating, shingles exhibiting flaking are prone to additional loss of granules from hail impact. The round and localized nature of hail impact damage helps to distinguish it from flaking damage, which often is irregular in shape and size. See Figure 4 for an example of flaking and algae growth.


Mechanical damage covers a broad range of incidents which may physically damage shingles or remove the granular roof coating, including golf ball strikes, tree limb contact, and in some cases intentional damage. Becoming familiar with these conditions will help the inspector properly identify damage caused by hail impacts.

Wind Damage Assessment

Just as for hail damage assessment, a working definition for wind damage must be established in order to properly evaluate asphalt composition shingle roof coverings, Accepted industry definitions and experience support the definition that wind damage typically manifests in one of three ways: torn or missing shingle tabs; creased shingles, and "hidden damage." Hidden damage is a phrase used to describe torn conditions that are not readily visible when walking on the roof.

Strong wind may completely tear or separate shingles or shingle tabs from the roof (see Figure 5). The phrase "shingle tab," refers to the exposed portion of the shingle. Common strip shingles may have three or four tabs. Some shingles have extra layers or laminations (often referred to as "architectural," "laminated," or "dimensional" shingles).


Wind damage is most common on the windward side of the building. Eaves, rakes, and ridges are often vulnerable due to increased wind pressures in these areas. A creased condition occurs when strong wind bends a shingle tab upward. If shingle tabs crease, it is an indication that wind was sufficient to bend back the affected shingle tab to the point where a line of exposed asphalt bitumen will form in the shingle at the area where it was bent back, typically close to the edge of the overlying shingle. Once the shingle creases, it becomes prone to tearing along the crease, especially if the wind causes repetitive lifting or flapping condition. See Figure 6 for example views of creasing and flapping conditions.


Wind may also damage shingles by separating or tearing them from their fasteners without removing them from the roof. This typically occurs to groups of shingles. This form of damage is often hidden since the affected shingles may return to their original positions, thus covering the underlying damage.

Because this type of damage is typically hidden, representative testing (gentle lifting using hand pressure) of the shingle is commonly required for identification. If a shingle tab is loose, the fasteners and surrounding shingle surfaces may be examined for torn conditions.

A torn condition may impair the shingle's ability to remain on the roof. See Figure 7 for example views of this type of wind damage.

An unsealed condition in and of itself is generally not considered to be wind damage because the shingle may be unsealed for a variety of reasons. Unsealed shingles do, however, make the roof covering prone to wind damage, since the unsealed condition may allow wind to more easily lift the affected shingle tab upward and bend it backward, resulting in a creased or torn condition. It can also allow the affected shingle to more easily tear or to pull from its fasteners (possible hidden damage).


The challenge for the inspector becomes the determination of whether or not the wind event caused or contributed to the unsealed condition of the shingles. An examination of the degree of transference between the sealing strip and the underside of the shingle may provide an indication of the adequacy of the seal prior to the storm event. That is, if there is no transference of the sealant between overlying shingles, the shingles were likely not properly sealed prior to the wind event.

The roof covering should be evaluated in its entirety, putting into consideration prevailing wind direction and other forms of damage that may accompany the unsealed shingles. The inspector should note any patterns in the unsealed conditions of the shingles. Unsealed groups of shingles at roof locations where wind pressures would tend to be greater may be consistent with wind damage, whereas localized unsealed shingle tabs that follow the installation pattern of the roof covering may not be consistent with the effects of wind.

When evaluating asphalt composition shingles for wind damage, special attention should be given to the fastening condition of the roof covering. Improper fastening will directly impact the susceptibility of the roof to wind damage. Proper fastening is of paramount importance to the performance of an asphalt shingle roof covering.

One of the most common improper installation techniques concerns the location of the fasteners. Installation of nails or staples on or above the sealing strip is referred to as "high-nailing." A nail or staple installed at a location significantly higher than what is re quired may miss the upper edge of the shingle underneath. This means that a reduced number of fasteners will hold the shingle, which has a direct bearing on its ability to resist wind pressures. A fastener that is installed over the sealing strip may hinder the shingle's ability to seal properly, which could make it prone to lift up, crease, and eventually tear due to wind events.

Another condition is missing fasteners, which has a strong impact on the shingle tab's ability to withstand wind pressures. A condition in which edge fasteners are missing is typically caused by a "racked" installation method. Racking is an installation technique where shingles are installed in a staggered column formation rather than in a stair-step pattern, as recommended by most manufacturers. One of the concerns of racked installations is the likelihood of omitting the last fastener on the shingle, because a blind-nailing condition will occur at every other course.

Another installation concern arises because of overdriven fasteners. Nail heads or staples are required to be flush with the surface of the shingle without penetrating its surface. Overdriven or angle-driven nails or staples may promote a tear around the fastener.


Below are the five basic steps for inspecting and evaluating a residential roof covering for storm damage.

* Prepare for the inspection by becoming familiar with the storm event and the area in which the residence is located. This may involve obtaining weather information, maps, and aerial photographs. The inspector must take adequate precautions to gain access to the roof safely for a detailed inspection.

* Interview the property owner/resident for their knowledge of the storm event, age of the roof covering, history of repairs, and so on.

* Inspect areas surrounding the roof for evidence of collateral damage or tell-tale markings. Examples may include fallen trees/limbs and other wind-blown debris; smooth, round, and randomly located indentations in metal materials (mailboxes, utility enclosures, etc.); and hail spatter marks (randomly located hail-impact markings on oxidized surfaces) on various objects such as electrical transformer enclosures and wood privacy fences.

* Inspect the roof covering. This should include observing all roof slopes to determine the general condition of the roof covering and to identify the general locations of any specific damage. A more detailed inspection of "test squares" (100-square-foot inspection areas) should then be performed to quantify specific damage when applicable.

* Formulate opinions based on the physical inspection and information gathered from various resources. Some research may need to be performed to determine if a particular roof covering has any known history of defects. It may be necessary to obtain the services of an independent engineer for assistance in the evaluation of a particular roof.

James W. Jordan, P.E., S.E., is vice president, national property division manager, for Rimkus Consulting Group, Inc., a forensic engineering firm. He is a civil/structural engineer licensed in ten states, and has more than 20 years of experience in design and forensic engineering work.
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Title Annotation:Feature Story
Author:Jordan, James W.
Date:Oct 1, 2010
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