Shingle Curling, Clawing and Cupping

Curling is the general name for asphalt shingles that no longer lie flat. Roofers and inspectors often split it into two patterns. Cupping describes the edges and corners turning upward so the tab forms a shallow dish. Clawing describes the middle of the tab lifting while the corners stay down, giving a humped look. Some sources also describe tab edges bending under. Whatever the name, a shingle that has lost its flat profile is more easily caught by wind, more prone to cracking, and may let wind-driven rain under the course above.

Causes

• Age and weathering. As the asphalt loses its oils it shrinks and stiffens, and curling is widely treated as a sign of wear. Older organic-mat shingles are especially prone to it.
• Heat and poor attic ventilation. An overheated, poorly ventilated roof deck can speed up ageing of the asphalt.
• Moisture from below. Damp attics or wet sheathing can make the underside of the shingle expand differently from the sun-baked top.
• Installation errors. High nailing, too few nails, shingles laid over an uneven old roof, or racked (straight-up) installation can leave tabs poorly held.
• Manufacturing defects in some product batches.

Identification

From the ground, curling shows as shadow lines, a ragged texture, or individual tabs that catch the light. Up close, the inspector checks whether the condition is uniform across the roof (pointing to age or ventilation) or limited to certain areas (pointing to installation, a wet spot, or a defective lot). Curled shingles may also be brittle; they can crack if bent or walked on, so inspections should avoid unnecessary foot traffic.

Remedies

A few curled tabs on an otherwise sound roof can sometimes be re-adhered with roofing cement or replaced. Widespread curling usually means the shingles are near the end of their service life, and the roof is generally planned for replacement. Correcting attic ventilation and moisture problems at that time helps the new roof last.