Why are my roof shingles buckling?

Roof shingles buckle, appearing as wavy, distorted, or wrinkled areas where shingles are lifted and not lying flat, due to movement or moisture underneath the shingles rather than aging of the shingle itself. The most common cause is moisture in the roof deck or underlayment. If plywood or OSB decking was wet or damp when shingles were installed, or if it gets wet from leaks or poor ventilation, it expands and pushes shingles up, causing buckling. Similarly, if roofing felt or underlayment was not installed flat and wrinkled before shingles were nailed, those wrinkles telegraph through and cause shingles to buckle. Another cause is improper deck spacing, as plywood sheets need a 1/8 inch gap between sheets to allow for expansion, and without it they swell and buckle when humid. Poor attic ventilation can also cause buckling by trapping heat and moisture that warps the deck. Improper installation of shingles, such as not aligning them properly or installing over an uneven existing layer during a layover, can also create a buckled appearance. Unlike curling which is shingle deterioration, buckling indicates a problem below the shingle, often with the deck or underlayment, and requires inspection. Minor buckling may be repairable, but widespread buckling usually requires tear-off to fix the deck condition.