What causes shingles to curl up?

Shingles curl up primarily due to aging, heat, and moisture imbalances that cause the asphalt mat to shrink and distort. The main cause is natural aging and loss of volatiles. Asphalt shingles contain oils that keep them flexible. After 15 to 25 years of exposure to ultraviolet radiation and daily thermal cycling, these oils evaporate, causing the shingle to shrink, become brittle, and curl. Cupping, where edges turn up, occurs when the top surface shrinks faster than the bottom. Clawing, where the center rises, occurs when moisture is absorbed into the mat. Inadequate attic ventilation dramatically accelerates curling. Without proper soffit intake and ridge exhaust, attic temperatures can exceed 150 degrees in summer, cooking shingles from below and causing premature oil loss and warping. Moisture from inside the home can also get trapped in the deck and cause shingles to swell and curl. Installation issues such as installing over a wet deck, using too few nails, or installing shingles in extreme cold without proper sealing can predispose them to early curling. Low-quality, lightweight shingles with less asphalt content curl faster than heavier premium shingles. Once shingles curl up, their ability to shed water and resist wind is severely compromised, and widespread curling means the roof is at end of life and needs replacement.