There are lots of techniques for shingling a valley–woven, cut, open metal lined–but there's one you just won't find described on shingle wrappers that's easier and faster to install, is just as weather resistant, and looks great. It works with laminated or random-pattern shingles that comprise about 65 percent of the shingles installed. The system goes together like a cut valley, but since there's very little cutting required I call it a "no-cut valley." You may never cut a valley again.
A no-cut valley starts out just like an ordinary cut valley. Prepare the valley by lining it with waterproof shingle underlayment like Grace Ice and Water Shield for secondary water protection. Determine which roof plane drains the highest volume of water into the valley and which one drains the least. Shingle the lower-volume roof plane first in a standard fashion.
Step by Step
Step 1: Prep the Valley and Shingle the Low-Volume Roof Plane
Line the valley with waterproof shingle underlayment for secondary water protection (shown at the top of the photo above). Shingle the low-volume roof. Run the shingles through the valley center and at least 12 inches up onto the high-volume roof. Be sure to press the shingles tightly into the valley center to avoid bridging. It's best if there are no shingle joints within 12 inches of the valley.
Step 2: Snap a Guide Line and Spread a Ribbon of Roof Cement
Snap a chalk line parallel to the valley 2 inches up from the center on the high-volume roof plane. Then, spread a 2–3-inch-wide ribbon of trowel-consistency roof cement about 2 inches over from and parallel to the chalk line on the high-volume roof side of the line.
Step 3: Run a Row of Shingles Up the Valley Along Diagonal Chalk Line
Here's where the no-cut valley distinguishes itself. Starting at the eave's edge, apply full shingles with the top edge aligned with the chalk line. Bed the shingles into the roof cement and drive fasteners along the shingles' nail line.
Step 4: Snap Course Lines and Shingle the High-Volume Roof
Strike horizontal chalk lines for the top of each shingle course on the high-volume roof to guide shingle installation. Register the bottom corner of the first shingle in each course to the valley edge of the diagonal shingles and fasten in place. Continue stacking the "starter" shingles up the whole valley to create a pyramid pattern, then shingle out of the valley. The diagonal run of the valley establishes a 5–6-inch shingle joint offset, a perfect starter pyramid for architectural shingles.
Step 5: Seal the High-Volume Roof's Shingle Corners
Seal the bottom corner of the high-volume roof shingles with a dab of roof cement to keep them down. Skip this on shingles with a self-seal strip on the underside rather than the face.
From the Ground Up
There's a lot to like about this method and only a little to get used to. While the hollow spots at the end of each no-cut starter shingle are noticeable standing on the roof, from the ground they vanish into the field of random shingle layers. And, the no-cut valley uses fewer shingles than a cut or woven valley. The extra row of shingles used to run along the valley edge is more than made up for considering the trim waste generated cutting a valley. There's less mess, too.
If that doesn't get your attention, then check your watch: No-cut valleys assemble in half the time of cut or woven valleys, and they're just as weather resistant.
–Mike Guertin, a home builder and remodeler in East Greenwich, R.I., is author of Roofing with Asphalt Shingles from The Taunton Press, and is a member of the JLCLive! and The Remodeling Show construction demonstration teams.