Cedar roofs are common in Eastern Massachusetts, where I live and work. They're typical of the antique homes around here that date back to the 1700s. Cedar is a premium material, but if you're aiming for authenticity when building a new Cape Cod–style home, that's what you install on top. More-durable western red cedar is the species of choice for roofing; Atlantic white cedar is best reserved for sidewall installation. In this article, I'll explain how I weave the valleys.
I prefer woven over open or butted valleys, both for their aesthetic appeal and because I believe they better resist leaks. While you can approximate the look of a woven valley by cutting and butting the opposing sides together, this still leaves a running seam that can trap wet vegetation and lead to premature deterioration. I close the seam by overlapping the two sides in an alternating sequence. This requires a compound miter cut on every valley shingle. I use a Bosch digital miter gauge to find the angle of intersection, or dihedral, of the two roof planes, then transfer the sheathing cut angle to the shingle with a Swanson's Wizard angle gauge. With my saw set to the dihedral angle, I cut the shingle to the sheathing angle.
But I'm not about to make all those cuts squatting in the valley. Instead, I prep the job by erecting a comfortable work platform at eaves level, atop pipe scaffolding, and then - to minimize ladder trips - set up the tools I need. I have a bench table saw for resizing shingles and cutting finishing courses, and a small worktable where I cut the compound angles.
To protect against ice dams, I install self-adhering membrane along the eaves, over the drip edge, to a point 2 feet inside the exterior wall, followed by a 36-inch-wide strip up the center. I then cover the roof with a synthetic roofing underlayment. I use lead-coated copper, custom fabricated at a local shop, for all my flashings because it will perform as long as the wood roof - which, installed over a ventilating substrate like Cedar Breather, can last for more than 50 years.
To accommodate the angle cuts and minimize piecework, I cull the widest shingles for the valley. It's easiest to work the courses from the valley out, rather than closing in from the field. In the valley, every shingle course is backed by a piece of lead-coated step flashing. Shingling the valley is a layering process that sounds like a bad marching cadence: "right, left, left, right, right, left, left," and so on.
I install the first valley shingle of the starter course, nailing about 1 inch above the exposure line and 6 inches out of the valley. I use 1 3„4-inch stainless steel ring-shank nails exclusively, with the gun pressure adjusted to set the heads flush with the surface. The opposing shingle goes on next, followed by a 12-by-12-inch square step flashing, bent corner-to-corner, with its lower tip held to the butt line and nailed at the two outside corners. The next course starts with a shingle on the same side as the shingle installed below it, followed by the opposing side. This repetitive sequence produces the back-and-forth "weave" that effectively closes the seam. Naturally, the starter course is a double layer. The built-up layers do change the angle of the succeeding cuts somewhat. I simply cut the shingles to the measured angle, then mark them in place and recut for a tight fit.
Subsequent courses follow the same order to the ridge, with no more than a 5-inch exposure per course. On the roof shown here, a lower ridge intersects the slope of an opposing roof. Rather than beating a piece of lead into a lumpy shape over the intersection, I had a piece of custom flashing made. One side of this particular intersection presented an irregular valley. Basically, because the courses can't be consistently aligned, an irregular valley forces an irregular weave. Each respective course must be fit to the opposing side as conditions demand, which means occasionally breaking the regular cadence. That's fine; it still looks good, and it won't leak.
Larry Perrault owns Perrault Builders in Sandwich, Mass.