According to YourDictionary.com, a valley is defined as “the trough formed where two adjacent slopes of a roof meet, or where the roof meets a wall.” Every pitched roof has one or more peaks, and some pitched roofs have one or more valleys. Valleys can be difficult areas in which to properly install composition shingles. Use any of three shingle installation methods devised to provide a watertight covering for valleys.
Whichever method is used to shingle the valley of a roof, prepare the roof similarly. Under composition shingles, install a waterproof underlayment on the plywood or wood decking or sheathing of the roof prior to shingle installation. Roofing felt is a fibrous paper material soaked in tar to become waterproof. It comes in rolls 3 feet wide and is manufactured in different weights or thicknesses. The heaviest felt weight used in roofing is called 100-pound felt.
Roll the first course of felt horizontally across the roof along the eave line, and staple it to the plywood decking. Overlap the next course of felt on the first course by 12 inches. Wherever the roof changes direction at a valley, cut the felt in the notch of the “V” of the valley. Lay the felt on the other side of the valley in the same way, also cutting the felt in the notch of the “V”.
Complete the valley preparation by either of two methods. In one method, install a line of felt down the length of the valley. Press the felt strip into the “V” and fasten it with staples on both sides of the “V.”
In the other option, install metal “V” flashing in the valley. Glue the flashing in place using roofing cement. This method is never used in conjunction with “W” flashing.
Galvanized Valley “W” Flashing
For the easiest method to shingle a valley, use galvanized valley “W” flashing. According to Home Time, “One type of flashing we recommend is galvanized steel, W-shaped valley flashing. It fits in the valley like typical 'V' flashing, but has a small ridge sticking up in the middle…” Install this flashing in the valley on top of the felt, beginning at the roof peak and continuing down the valley to overhang the eave by at least 1 inch. It protects the valley from moisture, channels water to the gutter and provides a clean look to the finished roof.
When a row of shingles makes contact with the flashing, cut the shingles so the shingle ends meet on either side of the small ridge in the middle of the “W” flashing. When you install the shingles properly, the ridge in the center of the “W” flashing will be exposed.
Woven Valley Method
For the woven valley method, do not use the “W” flashing, but instead use “V” flashing or felt as a preparation before installing the shingles. According to Inspector Now, “…shingles from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied. The valley flashing is not exposed…” This method is faster to install, but has some drawbacks. It does not provide a clean line when finished, and there is constant friction between shingles in the valley. Roofing material will expand and contract relative to temperature. The constant movement of the shingles in the valley will cause premature wear and reduce shingle life.
Closed-Cut Shingle Weave
Prepare to use the closed-cut method in the same manner as the woven valley method. According to Home and House, “A method of valley treatment in which shingles from one side of the valley extend across the valley, while shingles from the other side are trimmed 2 inches from the valley centerline. The valley flashing is not exposed…” This method is also faster, reducing friction between shingles in the valley, but it does not have a clean line when completed.
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