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Technical Notebook: Shingle Curling

An in-depth look at common shingle problems and roof claims.

By Charles C. Roberts, Jr., Ph.D., P.E. | Updated on December 31, 2010
Figure 1 is a photo of a typical glass fiber substrate asphalt shingle, a common roofing shingle used throughout the United States. A fiberglass mat is impregnated with asphalt and then coated with a ceramic grit called granules. Claims of roof shingle wind damage often arise when discovering curling of the shingle tabs after a severe wind storm (Refer to Figures 2 and 3). Curling is typically a long-term-related deterioration of the shingle brought on by a variety of causes not related to wind damage. 

Four typical causes of shingle curling are outlined below:

The purpose of the sealing stripis to hold the neighboring shingle tabs down to prevent curling or lift during high winds. If the shingles are installed improperly where the sealing strip does not line up with the next shingle according to the manufacturer’s recommendation, then the shingle tabs will not be secure and will curl upward or inward over time.

Improper nailing is a common cause of shingle curl. In Figure 1, the nails are placed according to the shingle manufacturer’s recommendations. In Figure 4 below, a nail has been driven into the sealing strip, which limits the effectiveness of the seal on the sealing strip. Over time, as a result of thermal cycles–heating during the day and cooling at night–the nail can back out, causing the shingle tab to lift and part from the seal, leading to curling as shown in Figures 4 and 5. In addition, insufficient nailing can lead to curling.

A lack of attic space ventilation is another cause of shingle curl. Moisture evolves in the attic as a result of moisture generation in the home and from the outside environment. Normally, moisture-laden air in a well-ventilated attic will be swept away by air flow and not cause a problem. In poorly ventilated attics, water vapor will increase and water will eventually condense on the roof sheathing. As the sheathing becomes moisture laden, shingle curling can occur. A lack of attic space ventilation can also result in high attic temperatures, which can reduce the effectiveness of the sealing strip adhesive, leading to curling over time. Most building codes require at least one square foot of free air opening for every 150 square feet of attic area. In homes with an acceptable vapor retarder, 300 square feet of attic space is allowed per one square foot of open ventilation area. Of course, attic ventilation openings should be distributed so that approximately 50 percent of the open area is at the ridge, with approximately 50 percent at the soffits.

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