Is it normal for roof shingles to buckle?

No, it is not normal for roof shingles to buckle, and buckling indicates an underlying problem that needs attention. Buckling appears as wavy, raised, or wrinkled distortions where shingles are not lying flat, and it is different from curling which is shingle aging. Minor waviness shortly after installation can be normal temporary settling that flattens within weeks in warm weather as shingles seal. However, true buckling that persists or develops later is abnormal. The most common cause is moisture or movement in the layers below the shingle. If plywood or OSB decking was wet when shingles were installed, or gets wet later from leaks or poor ventilation, it expands and pushes shingles up into buckles. Wrinkled underlayment installed with wrinkles will telegraph through and cause buckling when heated by sun. Improper deck spacing, where plywood sheets were installed tightly without a 1/8 inch expansion gap, causes sheets to swell and buckle in humidity. Installing new shingles over an existing uneven layer during a layover also causes buckling appearance. Poor attic ventilation trapping heat and moisture can warp the deck and cause buckling. While a small buckle might be cosmetic initially, buckled shingles are more vulnerable to wind uplift and water intrusion. Widespread buckling usually requires removing shingles to correct deck or underlayment issues.