Procedure for an Evaluation of Wind Damage to Shingles

Posted by in Archive 2004 thru 2011, Shingles | December 23, 2011

Since about 2003 it seems that the number of severe storms in Northeast Ohio have increased significantly. This has caused a significant increase in the number of hail and wind damage related claims for composite asphalt shingle covered roofs.

In previous years paying a non-meritorious claim for alleged hail or wind damage to an asphalt shingle covered roof might have been a prudent economic decision to resolve a few scattered or relatively inexpensive claims. However, the dramatic increase in the number and the scope of the claims being filed for hail or wind damage to shingles may no longer permit this approach to be considered as a prudent economic decision. Claims that require further consideration may be evaluated with a methodical approach so that damaged and undamaged roofs are handled fairly and properly.

A methodical approach to evaluating these claims requires a consistent and true procedure for the evaluation of hail and wind damage claims. Since we have already published an article that discusses the evaluation of hail damage (Shingle Damage Evaluation), this article will focus on the evaluation of wind damage to shingles.

When wind passes over and around a building, it generates inward or outward pressures on the walls and inward or outward (uplift) pressures on the roofs. Inward (positive) pressures are generated on the windward side of the building as the wind blows against a wall or roof surface such as a steep roof. This positive pressure does not damage shingles unless the tabs are lifted such that the pressure can get under the tab. Outward (negative/suction/uplift) pressures are generated when the wind passes by a wall, passes away from a wall (leeward side of the building, that is, the side not facing the wind), passes over a shallow sloped roof, or passes over the leeward slope of the roof. It is this negative or suction pressure that lifts a tab or a shingle strip.

Figure 1 Common wind pressures on a gable shaped dwelling. (From the National Research Council Canada)

Figure 1 - Common wind pressures on a gable shaped dwelling. (From the National Research Council Canada)

The magnitude of the positive or negative/suction pressures on the shingles of a building is determined not only by the speed of the wind, but also by the orientation of the roof slope to the direction of the wind and the location of the shingles on the roof slope. For example, the shingles at the edges of a windward roof slope are exposed to higher uplift pressures than the shingles near the center of the roof slope. This extra uplift pressure is generated at the edges by the additional pressures from the secondary movement of the wind as it encounters the wall and then rushes up over the roof (Figure 1). High uplift pressure are generally found along the eaves, along the rakes, along the ridge, along the hips, and along other discontinuities or changes in the roof surface.

Figure 2 Dashed line of asphalt sealant provides sticky surface for tab to contact and seal.

Figure 2 - Dashed line of asphalt sealant provides sticky surface for tab to contact and seal.

Shingle tabs resist the uplift pressures of the wind by sealing to the shingle strip under it. The sealing is accomplished with an asphalt sealant. The sealant is usually applied in a continuous or dashed line to the top surface of the shingle (Figure 2). The sealing is accomplished when the sun heats the roof and softens the asphalt and the weight of the shingle tab causes the tab to make contact with and sink into the softened asphalt sealant. The sealing of the tabs to the shingles strips below cause the individual shingle strips to be bonded together to form a continuous sheet. The sheet of shingles resists the uplift pressures of the wind through their fastening to the roof deck with nails driven approximately along the centerline of the shingle strip, particularly at both ends (sides) of the strip and intermediately at the third points. Thus, each shingle strip is commonly fastened with four nails. However, when the nails are properly located they also penetrate the top edge of the shingle below, thus, each shingle strip is commonly fastened with eight nails.

The Ohio Residential Code 2006 (ORC) requires that residential shingles be self-sealing or interlocking and comply with the Standard Specification for Asphalt Shingles (Organic Felt) Surfaced With Mineral Granules, D225 or the Standard Specification for Asphalt Shingles Made from Glass Felt and Surfaced with Mineral Granules, D3462, both published by the American Society for Testing Materials (ASTM). Both of these documents reference the Standard Test Method for Wind-Resistance of Asphalt Shingles (Fan-Induced Method), D3161-09 published by ASTM for evaluating adequate wind resistance.

As of the writing of this article in September 2010, the wind resistance of shingles are of three classes, Class A, Class D, and Class F. These are defined in ASTM D3161-09. Class A shingles pass a test wind velocity of 60 mph, Class D shingles 90 mph, Class F 110 mph. Although ASTM has specified a test for wind resistance, it notes in D3161-09 that the test results do not directly correlate to wind speeds experienced in service. They note that the test method for wind resistance does not include variations in intensity, duration, and turbulence that are found while shingles are in service. Nor does the test method consider temperature, time, roof slope, contamination by dirt and debris, or mis-alignment or misplacement of fasteners. Thus, a shingle of a particular class is not necessarily guaranteed to be capable of resisting the specified wind speed of that class while in service. However, a quick survey of shingle manufacturers seems to indicate that the test method specified in ASTM D3161 is used by the manufacturers to establish the wind speeds for their warrantees regarding wind resistance.

The manufacturers’ warrantees for wind resistance vary from 60 mph for the 20 to 25 year warrantee shingles to 130 mph for the lifetime warrantee shingles. The warrantees vary for a period of 3 years for the 20 year warrantee shingles to 10 years for the 25 year to lifetime warrantee shingles. The warrantee information indicates that a better and more expensive shingle is more capable of resisting higher wind speeds for a longer period of time. The warrantee information also indicates that wind speeds of less than 60 mph would not be expected to damage any properly installed and maintained shingle. The 60 mph expectation may be raised for higher quality shingles. Thus, wind damage to a shingle during a storm with wind speeds less than 60 mph is probably a result of factors other than exposure to high winds. Weather records may be obtained from the National Oceanic and Atmospheric Administration to determine the wind speed of a particular storm. Since manufacturers’ warrantees are for the peak gust wind, the peak gust wind should be the wind measurement considered in the evaluation. In addition to the weather records and the reports by eyewitnesses, the wind speed at the site may be estimated further by the damage or lack of damage to nearby objects. For example, the nearby wall siding, trim, window panes, tree branches and limbs, small trees, large trees, furniture, canopies, tents, antennae, satellite dishes, etc. may be examined for damages characteristic of exposure to excessive wind speeds. These reports and conditions may also be compared with wind damages described on tables such as the Beaufort Scale.

The damaged shingles also provide information helpful to the evaluation. The most common modes of failure during exposure to wind pressures are creasing, where the shingle tab is bent up and down until a crease or fold forms along the edge of the shingle tab above (Figure 3);

Figure 3 Shingle exhibits creasing from repeated lifting by wind.

flipping, where the tab is bent back over the overlying shingle(s) (Figure 4);

Figure 4 Shingle strip flipped back onto overlying shingles.

tearing, where the tab is not only creased but has detached and dislodged from the shingle strip (Figure 4); and a puncture or surface damage from the impact of debris.

Figure 5 Tab dislodged after unsealing and repeated lifting by wind near rake.

Modes of failure that may also occur during exposure to more severe wind speeds include the dislodging of full or partial shingle strips. Shingle strips may dislodge after tearing around or pulling over the nail heads. All of these occur predominantly at the areas of higher uplift pressures, such as the rake, the eaves, the hip, or at some discontinuities in the roof slope. Sometimes creasing, flipping, tearing, punctures, nail pull through (Figure 6), or dislodging of strips are not due to exposure to high winds, but due to poor nailing practice, poor quality or defective shingles, unintentional damage that occurs while probing the roof during inspection, or intentional damage.

Figure 6 Nail pulled through shingle. Note relatively clean surface at nail head.

Figure 6 - Nail pulled through shingle. Note relatively clean surface at nail head.

Where creasing, bending, flipping, tearing, punctures, dislodging, or nail head pull through occur on roof slopes in multiple directions, the pattern indicates that the damage may be a result of multiple events, some of which may be excessive winds. Wind damage on multiple roof slopes facing multiple directions requires wind to have traversed the roof from multiple directions. The shingles that exhibit these damages may be examined further for additional information. For example, weathered and/or discolored asphalt at the fractures or nail holes in the shingles (Figure 7); weathered, discolored, and/or dirt covered sealant; weathered, discolored, and/or dirt covered surfaces under the damaged shingle tab; and/or re-sealing of many of the previously damaged tabs indicate that these damages have been progressing over an extended period of time (Figure 9). A relatively clean and undiscolored asphalt (exhibits black color rather than faded gray) at the fractures or nail holes indicates that the damage occurred relatively recently (Figure 6). Nail heads that are set at an angle or that are over or underdriven may indicate that the nail pull through was due to poor nailing that cut into the shingle mat (Figures 7, 9 and 10).

Figure 7 Nail pulled through shingle. Note discolored surface at nail head.

Figure 7 - Nail pulled through shingle. Note discolored surface at nail head.

Figure 8 Tab exhibits evidence of previous re-sealing.

Figure 8 - Tab exhibits evidence of previous re-sealing.

Figure 9 Nail driven at an angle cuts into shingle surface.

Figure 9 - Nail driven at an angle cuts into shingle surface.

Figure 10 Proper nailing versus improper nailing. The creasing,

Figure 10 - Proper nailing versus improper nailing. The creasing,

The creasing, bending, flipping, tearing, or dislodging of a shingle tab may not be due to exposure to excessive winds, but due to the unsealing of the shingles by other phenomena. Unsealing of the shingle tab by other phenomena allows the tab to become loose, and thus, susceptible to lifting by the positive wind pressures or by the suction pressures of wind.

The unsealing of shingle tabs in itself is not wind damage. Unsealing is due to a failure of thesealant. A closer examination of the shingle tab may provide evidence to determine the cause of the unsealing. The bond of the sealant may have been broken as the tab and the shingle strip(s) below repeatedly expand, contract, shrink, or swell excessively relative to each other and/or the strength of the sealant was weakened by poor installation, a defect in the sealant, and/or the normal deterioration of the sealant over the years.

A shingle tab spanning across the joint between two shingle strips is more susceptible to differential movements as there is increased differential movement between the two adjacent shingle strips under the tab. A pattern of damaged tabs located over the joint between two adjacent shingle strips indicates that the unsealing is due to the breaking of the bond by excessive differential movement across the joint of the two adjacent shingle strips.

A small amount of sealant that has adhered to the underside of the shingle tab and/or the weathered, discolored, dirt covered condition of the sealant indicate that the sealant was contaminated before it could soften and bond to the underside of the tab above or that the asphalt sealant was defective. A defect in the sealant may be evidenced by the small amount of sealant applied to the shingles; a hard, relatively inflexible sealant; and/or a sealant that does not soften adequately when exposed to heat from the sun.

Poor installation also includes the installation of the shingles late in the year when the sealant was unable to soften from the heat of the sun and stick to the underside of the tab; the coating of the sealant with dirt prior to installation by poor storage, poor handling, or excessive aging of the shingle strips; the high, overdriven, underdriven, angled or mislocated placement of the nail which may cause the tab to lift; and/or the lack of nails near the ends of the shingle strips that allow the shingles to move excessively.

A shingle tab that exhibits patches of granules and/or asphalt dislodged from the shingle below or patches of asphalt dislodged from the underside of the tab above are considered by many in the industry to be evidence of damage from exposure to excessive wind speeds. However, the dislodged patches of granules and/or asphalt may have occurred unintentionally during the lifting of the tab during inspection or may have occurred intentionally. The pattern of the tabs exhibiting dislodged patches, the presence of tool marks, the presence and pattern of tearing indicative of excessive finger/hand uplift, or other physical anomaly can reveal the cause of the unsealing. Intentional hand tearing may often be identified by the peculiar pattern and/or particular path of the tear, and/or other features in the damaged shingles (Figures 11).

Figure 11 Shingle tabs torn by hand.

Figure 11 - Shingle tabs torn by hand.

Figure 12 Shingle tabs torn by hand.

Figure 12 - Shingle tabs torn by hand.

Unsealed shingle tabs may be the result of inadequate maintenance. It is an accepted industry practice that an asphalt shingle should be inspected at least once per year or more to seal unsealed or poorly sealed tabs by hand with an asphalt roofing cement approved by the shingle manufacture. This is a regular maintenance issue and is required to reduce the risk of damage from winds because unsealed or poorly sealed tabs are more vulnerable to lifting by normal and expected wind.

Finally, the curling at the corners of a shingle tab is not wind damage (Figure 13). An intermittent vertical pattern of curled corners is due to excessive lifting of the shingles during installation to install nails intentionally omitted when the shingles had been installed in a racked pattern. Curling observed at a three foot spacing indicates that it is due to excessive shrinkage of the shingle tab which has caused the tabs at the ends of the strip to unseal. A widespread pattern of curling indicates that there has been normal shrinkage on the top surface due to aging or swelling on the underside due to the absorption of excessive airborne moisture that has migrated through the deck from the attic.

Figure 13 Tabs unsealed over joints between shingle strips.

Figure 13 - Tabs unsealed over joints between shingle strips.

In closing, the cause of damage to shingles proposed to be due to exposure to excessive winds requires methodical consideration. The evaluation includes the consideration of the manufacturers’ expectations for shingles as described in shingle warrantees, a review of the weather data, the reported weather conditions prior to the reported discovery of the damage, the review of surrounding objects for wind damage, the review of the pattern of the damage, and the close-up examination of the shingles themselves. All of these provide clues to identify the true damage-producing mechanism.

(With updates on June 20, 2014)

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