Why do roof shingles curl up?

Roof shingles curl up due to a combination of natural aging, heat, and moisture imbalances that cause the asphalt and fiberglass mat to distort. The primary cause is loss of volatiles and protective oils from the asphalt due to prolonged UV exposure and thermal cycling over 15 to 25 years. As the asphalt ages, it shrinks, causing the shingle to contract unevenly. Cupping, where edges curl upward, happens when the top surface of the shingle shrinks faster than the bottom, pulling the edges up. Clawing, where the center lifts, can occur when moisture is absorbed into the mat from below due to poor attic ventilation or leaks, causing expansion underneath. Inadequate attic ventilation is a major accelerator, as excessive heat buildup in the attic cooks shingles from below, accelerating oil loss and causing them to warp. Improper installation, such as installing over a wet deck or without proper underlayment spacing, can also trap moisture and cause curling. Low-quality shingles with less asphalt and thinner mats are more prone to early curling. Once shingles curl up, they lose their ability to shed water effectively and their wind resistance drops dramatically, as wind can get under the curled edges. Widespread curling is a definitive sign that the roof has reached end of life and needs replacement.