Woven Valleys – Construction for Dummies
In our continuing series of Construction by Dummies, we discuss woven valleys for asphalt shingles.
A woven valley is one method of installation for asphalt shingles at a valley where two intersecting roof slopes meet (see featured photo above). It is a method where the valley is completed by overlapping and weaving the shingle courses rather than cutting the shingles back to form a trough lined with a sheet metal flashing (see Figure WV-1). Woven valleys still require membrane flashing or multiple layers of roofing paper to line the valley under the shingles. From our observations, the difficult feat appears to be to align the weave with the centerline of the valley (see featured photo above).
The alignment doesn’t need to be perfect, but it needs to be reasonably close. Particularly, the ends of the strips and the slots between the tabs should not be set such that they are set upslope from the valley, perpendicular to the downward flow of roof runoff, as seen on the featured photo above. Setting the ends and/or the slots up the slope, away from the centerline of the valley perpendicular to the flow, allows roof runoff to be directed under the tabs and/or strips.
The woven valleys seem to be gaining in popularity as they require fewer materials, and thus are less costly, but they require more planning and measuring. Some prefer the appearance of the woven valleys, but both appearance and weather tightness may be lacking if the weave is not aligned with or very near the centerline of the valley (see featured photo above).