What is buckling?
Buckling is defined as ridges that form along the length of the shingle, with the ridge spacing usually coincidental with deck board joints. These ridges are caused by the shingle being distorted from the movement of the deck. Buckling can occur with any deck type, but is more common with board decks, and less common on plywood decks. Buckling can occur when a new roof is installed, even if the old roof did not show any buckles; when the roof is stripped, the deck may be exposed to moisture, causing dimensional changes in the supporting lumber.
