Following installation, how is counter-flashing positioned in relation to the step or base flashing?

Counter-flashing is a critical component of roofing systems, specifically when dealing with roof penetrations such as chimneys or walls that intersect the roof plane. Its primary function is to direct water away from these areas and prevent potential leaks.

In relation to step or base flashing, which is installed first along roof edges or around penetrations, counter-flashing is positioned and secured in a manner that creates an effective barrier to water ingress. Proper installation involves folding the counter-flashing downward over the step or base flashing. This configuration allows water running down the face of the wall to be directed away from the roof, effectively channeling it into the step flashing underneath.

This method ensures that any water that might collect on the wall or surface above the flashing is directed away from the roof, thus minimizing the risk of leaks and improving the roof's overall waterproofing effectiveness.

Considering the options provided, the technique of folding the counter-flashing downward ensures the most reliable defense against moisture intrusion compared to other potential methods, which do not create the same level of protection or may even create channels for water to penetrate.