The Two Types: Cupping vs. Clawing
Roofers usually describe curling in two patterns. Cupping happens when the outer edges of a shingle turn upward, leaving the center lower, like a shallow bowl. Clawing is the opposite, where the center bulges up while the edges stay anchored. Both shapes break the flat, overlapping seal that sheds water.
Once a shingle loses contact with the deck, wind can get underneath it, rain can drive sideways into the gap, and the exposed underside weathers far faster than the surface designed to face the sky.
What Causes Shingles to Curl
Several issues lead to curling, and often more than one is at play:
- Age: As shingles lose their oils and asphalt dries out, they shrink and pull at the edges.
- Poor attic ventilation: Trapped heat and moisture bake shingles from below and warp them.
- Moisture absorption: Wet felt or decking swells and forces shingles out of plane.
- Improper installation: Overdriven nails, mismatched layers, or skipped underlayment accelerate distortion.
Why Curling Matters in the Spokane & Inland Northwest Climate
Our region puts curled shingles under unusual stress. Spokane and North Idaho roofs face heavy snow loads, repeated freeze-thaw cycles, and ice dams along the eaves. When a shingle is already lifted, meltwater and ice can wedge into the gap, freeze overnight, and pry the shingle further open, a cycle that widens cracks every cold snap.
Curled edges also catch our Palouse and ridge-line winds, making blow-offs more likely during the next storm. Because curling exposes the underlayment and nail heads, it is one of the most common early warnings that a roof is losing its weatherproof seal and heading toward leaks.
Can Curling Be Fixed, or Is It Time to Replace?
A handful of curled shingles from a localized issue, such as a missed nail or a small ventilation problem, can sometimes be repaired by sealing or replacing the affected pieces. Widespread curling across the whole roof is different. It usually means the shingles have reached the end of their service life and a few patches will not restore the protective layer.
If you are seeing curling on most slopes, a professional inspection can tell you whether targeted repair or a full roof replacement makes more sense before winter arrives. DG Contracting offers a free, no-pressure assessment so you know exactly where your roof stands.