Which component of roofing is responsible for preventing water from entering the structure?

Flashing is the component specifically designed to prevent water from entering a building's structure. It typically consists of thin pieces of metal or other waterproof materials strategically placed in critical areas of the roofing system, such as around chimneys, vents, skylights, and anywhere there are joints or transitions. The primary function of flashing is to direct water away from these vulnerable spots and ensure that it flows down and off the roof rather than seeping into the underlying materials and potentially causing leaks or water damage.

While other components such as the deck, sheathing, and eave play roles in the overall roofing system, they do not serve the primary function of water barrier protection. The deck provides structural support for the roofing, the sheathing is the layer that provides a flat surface for roofing materials, and the eave is the edge of the roof overhanging the side of a building. None of these components specifically addresses the need to manage and prevent water intrusion as effectively as flashing does.