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:
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.
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.