When the front edge of a shingle tab lifts to form a shallow “U” saucer shape in cold weather and flattens when the weather is warmer, this phenomenon is known as winter curling. Sometimes, the entire front edge of a shingle may lift uniformly.
When the top surface of the shingle is cooled, this part of the shingle contracts. At the same time, the bottom of the shingle receives a certain amount of heat from the attic, especially if the attic ventilation is insufficient. As a result, the shingle curls slightly.
The appearance of winter curling depend on: the age of the shingle, whether the attic is sufficiently ventilated, the type of shingle, roof pitch, humidity and climate. Complete elimination of winter curling is rare, although the durability and watershedding properties are not affected.