When the corners of the shingles turn up, it is referred to as ‘curling’. This is usually caused by excessive moisture that is present in the underside of the shingle. Heat and moisture can get trapped in the attic due to inadequate ventilation. This buildup of the heat and the moisture will eventually penetrate into the roof deck and this causes the shingles to curl. To solve this issue, you should consider improving the air circulation within the attic. This can rectify the solution and the curling will not be too severe.