Which component is most likely to fail if shingles split during contraction of roof materials?

Shingles are typically secured in place by an adhesive strip, which helps to create a seal that protects the roof from water infiltration. When temperature changes occur, roofing materials expand and contract. If shingles split during this contraction, the adhesive's integrity is compromised. This means that the bond created by the adhesive strip is most susceptible to failure.

When shingles are not properly bonded due to splitting, they may lift or create gaps that allow water to seep beneath them, leading to potential leaks and further roof damage. The adhesive strip is critical for maintaining the weather-tight integrity of the roof system, which is why it is the component most likely to fail under these conditions.

The other components listed, such as tar bond, plywood sheathing, and roofing underlayment, serve different functions. While they each contribute to the overall performance of the roofing system, they do not directly hold the shingles in place as the adhesive strip does. Therefore, their failure wouldn't be the immediate concern related to splitting shingles during contraction.