There are three main ways to install a shingle valley. First is the correct way, by fully lacing the low side plane through the valley so a full shingle is in the valley protecting the flashing and then the second plane is installed and cut straight with the valley center. Second it a full lace valley where both sides are laced through the valley. This causes “bridging” or uplifting of the shingles and leads to seepage. Third, which is both least expensive and allows the most number of leaks, is by cutting the shingles before they lace through the valley by installing a “W” type valley metal. This is a major installation shortcut as it saves in both shingle and labor expense. However, the biggest issue with this type of installation is the seepage problems it causes. By cutting the shingles without lacing all the way through the only form of protection is a small bead of sealant on either side of the valley. On roof with a pitch over 5 in 12 the issue is more prevalent as the water jumps over the center valley ridge and is driven under the shingles. This Sanibel Island roof has been installed with an open valley and is showing signs of sealant breakdown, which may be allowing seepage.