To prevent moisture intrusion behind sidewall flashing, what type of flashing should be installed?

The correct choice for preventing moisture intrusion behind sidewall flashing is counter-flashing. Counter-flashing is specifically designed to overlap with the upper layer of roofing materials, creating a shield that directs water away and prevents it from seeping behind the flashing. This is particularly important in areas where the wall meets the roof, as moisture can easily penetrate if not properly managed.

Counter-flashing works by forming a barrier that integrates with the shingles or roofing material above, allowing water to flow over the flashing rather than behind it. This helps protect the structure from potential water damage, mold growth, and deterioration of building materials.

While other types of flashing, such as downspout, base-flashing, and continuous flashing, serve important functions in diverting and managing water, they are not specifically designed for the scenario described. Downspouts direct water from gutters to the ground, base-flashing is used at the base of walls or roof membranes to prevent water from entering wall systems, and continuous flashing extends along the entire length of a roof plane, but they do not specifically address the prevention of moisture intrusion in the context of sidewall applications like counter-flashing does.