To understand what makes a valley either closed or open it is important to understand how a valley is constructed.
Roof valley shingle weave.
Weaving a shingle valley by dunn contracting 727 410 5717 james dunn.
Woven valleys should only be used with strip shingles.
A woven valley shingle installation is one where the shingles from both sides of the roof valley extend over the valley and weave together overlapping courses alternately.
Closed valleys or open valleys.
The woven valley shingle installation method does not call for roofing cement relying instead on the weave pattern to protect from water infiltration.
Water has a small chance of even getting up under the woven valley shingles even though it flows in either direction.
So if you are installing a woven valley you must push the shingles snugly into the valley while not nailing within six inches of the valley center.
Pros of woven valley shingle installations.
Here we have a laminated shingle roof that has been installed with a woven valley detail.
There are two common methods for completing the flashing of a valley in a shingle roof system.