Evaluating Wind Damage to Asphalt Shingles
Robert Rutherford
Cook Claim Services
Asphalt shingles have been utilized as a roofing material for more than a century. Advancements in mat and sealant technology led to asphalt shingles becoming the primary choice for steep slope roofing. It is estimated that four out of five homes are roofed with asphalt shingles. A growing number of smaller commercial buildings also utilize asphalt shingles.
Although asphalt shingles can be rated for high wind zones up to 150 miles per hour as a three-second gust, wind damage to asphalt shingles is one of the most common types of roof claims. Wind damage is sometimes openly obvious and sometimes requires a closer inspection. High winds can damage roof shingles by tearing, warping, creasing, or lifting.
Asphalt shingles resist wind uplift by two methods. First, shingles are nailed in place, providing a mechanical connection to the roof decking. Shingle roof systems shed water to prevent leaks, so the fasteners securing each shingle are overlapped by the next shingle course. Adhesive sealant strips provide the second method by which asphalt shingles resist wind uplift. A sealant strip is applied to the underside of each shingle during the manufacturing process. Once the shingles are installed, radiant heat from the sun warms the shingles and bonds or seals the shingles together. A well-bonded sealant strip prevents shingles from being lifted by wind pressure. If the sealant strip has developed full strength, the shingles cannot be separated without tearing or delaminating.
Manufacturer warranties for wind resistance vary from 60 mph for the 20- to 25-year warranty shingles to 130 mph for the lifetime-warranty shingles. Warranties vary for a period of three years for the 20-year warranty shingles to ten years for the 25-year to lifetime-warranty shingles. This indicates that a better shingle resists higher wind speeds for a longer period and that wind speeds of less than 60 miles per hour would not be expected to damage any properly installed and maintained shingle. Thus, wind damage to a shingle during a storm with wind speeds less than 60 miles per hour is probably a result of factors other than exposure to high winds. Weather records should be obtained to determine the wind speed of a certain storm. Since warranties are for the peak wind gust, this particular wind measurement should be considered in the evaluation.
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; flipping, where the tab is bent back over the overlying shingle; tearing, where the tab is not only creased but has detached and dislodged from the shingle strip; and a puncture or surface damage from the impact of debris.
Exposure to more severe wind speeds may cause the dislodging of full or partial shingle strips. Shingle strips may dislodge after tearing around or pulling over the nail heads. Sometimes creasing, flipping, tearing, punctures, nail pull through, 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.
Where damage occurs 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 following findings may suggest that damages progressed over an extended period of time: (1) weathered or discolored asphalt at the fractures or nail holes in the shingles; (2) weathered, discolored, or dirt covered sealant; (3) weathered, discolored, or dirt covered surfaces under the damaged shingle tab; or (4) re-sealing of many of the previously damaged tabs.
A relatively clean asphalt (exhibits black color rather than faded gray) at the fractures or nail holes indicates that the damage occurred relatively recently. Nail heads that are set at an angle or that are over- or under-driven may indicate that the nail pull through was due to poor nailing that cut into the shingle mat.
Although wind may lift an unsealed shingle, wind does not cause a sound shingle roof system to become unsealed. Shingles are considered wind-damaged when they are torn, creased, or detached from the roof. Most commonly, wind damage occurs when three-tab shingles are creased by repeated lifting or flapping. Unsealed shingles without physical mat damage are not considered wind damaged.
The two most common factors that cause shingles to become unsealed are a failure of the sealant strip to properly activate following installation and age-related deterioration. Factors such as prolonged storage of the shingles (warehousing), improper installation, and manufacturing deficiencies can reduce the effectiveness of the sealant strip. As the shingles age, the adhesive bond of the sealant strip degrades and weakens until the shingles become loose. Shingles that are loose or unsealed could develop a weak bond following exposure to warm temperatures. Shingles that reseal in this manner are not expected to develop the full-strength bond of a sound roof system. Most unsealed shingles should not be expected to reseal but can be hand sealed with roof cement.
Curling (sometimes called cupping or clawing) at the corners of a shingle tab is not wind damage. An intermittent vertical pattern of curled corners is due to excessive lifting of the shingles during racked pattern installation. 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.
The cause of damage to shingles proposed to be due to exposure to excessive winds requires a detailed evaluation including the consideration of the manufacturers’ expectations for shingles as described in shingle warranties, a review of 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 cause of damage.
If you would like to contact Mr. Robert Rutherford regarding this subject, please call him at (601) 824-6066 or e-mail him at Robert@cookclaims.com for more information.