Asphalt based shingles have four layers. During the aging process the two asphalt layers begin to contract around the base mat layer. The base mat layer is commonly a fiberglass layer and will not shrink. As the asphalt layers contract they will pull on the mat layer causing it to pull away from the layer of shingle underneath giving the edge a curl look.
Typical curling looks like this with shingle roofs:
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It is rare to find curling in shingles younger than 12 years of age on a roof. If it does exist for young shingles, you may have a more serious problem than just the shingle. Curling in young shingles is commonly sourced from improper ventilation in the attic. Other causes include improper installation, poorly made shingle or even the wrong shingle type on your roof.
Curling with shingles older than 12 years of age is not uncommon, but it is a sign the shingle is in its second half of life. During the 2nd half of life, shingles deteriorate at an accelerating rate. Thus, it is a good idea to have your roof inspected by a certified inspector. Inspectors determine the remaining life of the roof membrane, identify potential or existing issues and provide guidance to the property owner of the next best set of steps to maintain roof integrity.
Understanding the Difference: Cupping vs. Clawing
When homeowners notice curling, it generally manifests in two distinct ways, each pointing to different underlying issues:
Cupping: This occurs when the edges of the shingle turn upward, creating a concave shape in the center. This is most often a sign of moisture trapped under the shingle or extreme heat in the attic “baking” the shingle from beneath.
Clawing: This is when the edges stay flat but the center of the shingle bulges upward, or the tabs curl downward. Clawing is typically a sign of an aging roof where the asphalt has become brittle and is losing its grip on the fiberglass mat.
The Hidden Danger: Why Curled Shingles Fail
Curling is more than an aesthetic flaw; it is a structural failure of your roof’s primary defense system. Once a shingle curls, it becomes highly susceptible to wind uplift. Because the shingle is no longer flat, wind can easily catch the edge and tear the tab off entirely.
Furthermore, curling creates gaps that allow rain to be driven underneath the shingles by the wind. Once water bypasses the shingles, it relies entirely on the underlayment. If your roof is over 12 years old, that underlayment is likely as brittle as the shingles, leading to fast-spreading leaks, deck rot, and mold growth in your attic.
Common Culprits: Beyond Just Old Age
While natural aging is the most common cause, premature curling can be triggered by:
Poor Attic Ventilation: If heat and moisture cannot escape the attic, the shingles are essentially “cooked” from both sides. This accelerates the contraction of the asphalt layers.
Layering Shingles (Roof-Overs): Installing new shingles over an old layer can trap heat and moisture between the two, causing the top layer to curl much faster than a single-layer installation.
Manufacturing Defects: Occasionally, shingles fail to seal properly during installation due to a lack of thermal adhesive or a “dry” asphalt mix during production.
When to Take Action
If you notice curling on more than 10-15% of your roof surface, it is no longer a localized repair issue. At this stage, your roof has entered its “terminal phase.” A professional NRCIA-certified inspection can determine if you have a few years of life left through targeted maintenance or if a full replacement is necessary to protect your home’s interior.
The National Roof Certification and Inspection Association trains and certifies roof inspectors across the country. If you wish to be placed in contact with a Certified Inspector, fill out this NRCIA Contact Form and a qualified inspector will reach out to you.