What causes roof shingles to curl up?
Short answer. Shingles curl when the asphalt loses its oils with age and heat, when an attic runs hot and damp from poor ventilation, or when installation mistakes such as high nailing or roofing over old shingles let the edges pull loose. Widespread curling usually means the roof is near the end of its life.
Two kinds of curl
- Cupping. The bottom edges of the tabs turn up. Often from age and heat drying out the asphalt, or from moisture under the shingle.
- Clawing. The edges stay down while the middle of the tab rises in a hump. Common on aging shingles and on roofs with attic moisture problems.
The usual causes
- Age and Georgia heat. Long, hot summers drive volatile oils out of the asphalt. As the top surface shrinks faster than the bottom, the shingle bends.
- Attic ventilation. A poorly vented attic heats the deck from below and traps moisture from bathroom fans or dryers that vent into the attic. Shingles over these areas often curl first.
- Installation. Nails placed too high, missing starter strip, or shingles laid over an old layer that is not flat all let edges lift.
- Older organic-mat shingles. Shingles made on a felt mat, common on older roofs, absorb moisture and curl more than fiberglass-mat shingles.
- Product problems. Occasionally a batch defect shows up as curling across the whole roof within a few years. Keep your warranty paperwork.
Why it matters
A curled edge catches wind, lets rain blow underneath, and is easily broken by hail. Insurers usually treat curling as wear and tear rather than storm damage. Spot replacement rarely blends in on an aging roof, so widespread curling usually means planning a replacement.
If the curl is concentrated on one area, look at the attic above that spot before blaming the shingles. Learn more in attic heat and shingles, heat and humidity and roof life, and signs you need a new roof.