Which material is used to prevent water leakage at joints?

Flashing is the correct answer because it is specifically designed to direct water away from joints and prevent leaks in roofing and construction. Typically made from materials like metal, rubber, or PVC, flashing is installed at critical areas such as roof joints, chimneys, skylights, and wall intersections. Its role is essential in ensuring that water does not infiltrate the structures at these vulnerable points, thereby enhancing overall waterproofing.

In contrast, ridge refers to the top edge of a sloped roof and does not serve a waterproofing function. The deck, typically a flat or sloped surface of a roof, provides structural support but does not inherently prevent water ingress at joints. Dormer refers to a window that projects from a sloping roof and is not related to water management at joints. Thus, flashing is the material specifically engineered for preventing water leakage at structural joints.