Which type of valley is less likely to create leaks when using flat shingles?

The closed cut valley is considered less likely to create leaks when using flat shingles due to its construction method. In a closed cut valley, the shingles from one slope are installed up to the valley line, and the shingles from the opposite slope are cut back, creating a clean edge that directs water down into the valley. This design helps to prevent water from getting trapped and promotes effective drainage, reducing the chances of leaks.

The precise alignment of shingles combined with the lack of overlapping layers in the valley area minimizes vulnerability to water infiltration. It effectively channels water, reducing the risk of leaks that can occur from other designs that may allow water to pool or trickle underneath the shingles.

In contrast, open valleys may not have the same level of direct water management as they typically do not feature shingles that are cut to a precise line along the valley. This can potentially allow for issues if debris or granules build up. Diagonal valleys and woven valleys have their own unique challenges and may not perform as effectively in certain conditions when compared to a properly executed closed cut valley.