To the left is a photo of one problem we've encountered with the metal valley. We've seen it many times. It's why we no longer install it. There are still companies that promote this outdated style of valley. These are probably the same companies that would have spoken ill of the fibreglass shingle when it first appeared in the industry. We are now observing the trend moving in favor of fibreglass, and organics are becoming obsolete.
Above is the before shot. Water rushes down the steeper slope at a fast rate and crashes down, under the shingles of the lower sloped side. Above, right: Removal of the shingles on the low pitch reveals the water that was sitting below. Lower, right: Low slope shingles wrap up under the shingles of the steep roof. The steep roof is shingled last and cut. When water comes down now, it cannot get under the shingles. This valley is located above a newborn's bedroom. Luckily, it was found and repaired before mold formation.