Is there a set distance that shingles should be laid from the center of a metal valley?


Buck, this might help you a bit here;

**ROOFING: Flashing **


Valleys can be open, closed, or woven (in the case of asphalt shingles), but it’s almost always worthwhile to provide more than one level of protection at this juncture. Figure 3-71 illustrates a “belt and suspenders” approach to valleys that is prudent in harsh climates.

Woven Valleys
Woven valleys can be quite durable if done right. • Shingles must extend at least 12 in. beyond the centerline (Figure 3-72). • Before shingling, line the valley with 55-lb. roll roofing or with self-adhering eaves membrane.

Closed Valleys
Closed valleys have clean lines, but if done wrong they can trap ice and debris. The covering course of a closed valley must be cut back a couple of inches from the centerline so that water flows away from the cut edge rather than into it (Figure 3-73).

Open Valleys
On an asphalt roof, an open valley may be lined with two layers of roll roofing. On all other roofs, metal valley flashing is the only long-term choice (Figure 3-74). Some critical aspects of a metal valley flashing are its width, length, the configuration of its centerline and edges, and the way that it’s fastened.

Width. A valley must channel runoff from two roofs, while having a shallower slope than either. It’s critical that the valley be designed to handle the flow:

• At the peak, a valley should be 5 or 6 in. wide on either side of the centerline.

• As it descends toward the eaves, it should widen 1/8 in. for every foot of run.

Length. To avoid excessive expansion and contraction, use 8- to 10-ft. lengths of metal, maximum, for valley flashing.
• Avoid using aluminum, which expands at a greater rate than other metals.

• Lap sections 8 in. minimum.

Centerline. When a steep roof intersects a shallow one, water cascading down the steep roof can overshoot the valley and run up beneath the shingles on the shallow one. Roofs like this need a valley flashing with a crimped centerline. The steeper the roof, the more critical the crimp will be.

Edge treatments. Like all roof flashings, valley flashings should have hemmed edges. Not only do these shed water more effectively, but by holding the shingles away from the flashing, they prevent capillary

Fasteners. Metal valleys can be fastened with nails or cleats at 2 ft. o.c. (Figure 3-75).

• Cleats are better; they won’t become fatigued and shear when the metal expands and contracts.

• When using nails, place them at least 5 in. away from the valley’s center to prevent leaks.

The Code on Valleys
CABO requires that metal valleys be fabricated from no less than No. 28-gauge corrosion-resistant sheet metal.

• For asphalt shingles, valley flashing must extend at least 8 in. on either side of the centerline.

• For wood shingles, the wings of a valley must extend 10 in. each way.

• For slate, tile, and wood shakes, a valley must extend 11 in. each way.

• Sections of flashing must have an end lap of at least 4 in. for wood shingles

Duplex receptacles.
Electrical codes require a duplex outlet at each end of any island (see Chapter 5, “Receptacles,” pages 37–38, for placement requirements).