1 Answer

jack the roofer:  Here you go:

To shingle out of the valley with laminated shingles, lay a shingle down as a gauge and mark the corner at the bottom (left) and top (right) of the roof.

I then move the shingle to the uppermost course on the roof plane, line up the mark on the shingle with the valley center and again mark the corner. A chalkline snapped between this mark and the lower mark forms my guide line.

After snapping the guide line between marks, install the shingles with one corner on the line. Snap a chalkline 3 in. from the valley, and you're ready to complete the valley.

I always weave my first course. But after that I run the shingles up the valley, aligning the top edges with the course lines and the top outside corners with the guide line. I nail the shingles normally, except that I keep nails at least 6 in. away from the valley center. Now I'm ready for the other roof plane.

Closed-cut valley -- Even if I work toward the valley with three-tab shingles, cut valleys are faster than woven valleys hands down. With a closed-cut valley, there's no need to shingle the two roof planes at the same time. Plus, cutting the closed-cut valley shingles can happen after the rest of the roof is shingled.

I begin the second side (the side that will be cut) by snapping a cutline 2 in. to 3 in. from the valley center. Keeping the cutline away from the center of the valley creates a better watercourse for runoff and tends to hide discrepancies in the line after the shingles are cut.

http://www.roofer911.com/roofing-articles/roofing-valleys.htm