The underlayment sheet metal liner if required and initial shingle covering into or through the valley follow the same guidelines for the standard closed cut valley and open valley construction.
Open cut valley roofing.
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The metal is usually pre painted to best complement the shingles color blend.
With an open valley a strip of metal will be visible on the roof wherever two opposing roof planes meet.
For an open valley a sheet of metal usually steel sometimes copper is fastened to the roof deck.
Roofing shingles are installed then cut and sealed where they overlap the metal channel.
Install synthetic roofing underlayment or felt paper according to manufacturer specifications and then install the first piece of valley flashing.
When to choose a closed valley over an open valley.
Fold the top over the roof ridge and cut the bottom along the drip edge metal.
The valley lining whether asphalt or metal should have 6 inches open at the top 3 inches on either side of the valley centerline and increase by 1 8 inch for each foot of valley length to accommodate the greater flow further down the valley.
A basic demonstration for roofing contractors and homeowners on how to install gaf timberline shingles using the closed cut valley method.
For a closed cut valley the installer should snap a chalk line 2 inches from the center line on the cut side.
The shingles are then cut out of the valley area opening the surface of the valley lining to water run off and the environment.
Open valleys may be susceptible to water backup if the cut off shingles are not properly trimmed potentially causing roof leaks.
The closed cut valleys are cheaper and commonly done in my area but they tend to wear out sooner due to the high volume of water in the valley washing away the protective grit on the shingles there before on the rest of the roof.
However it is said that provided the rest of the roofing shingles were properly installed and are performing properly open valleys will perform better over time than closed valleys.
If homeowners are looking to have their roof last for many years an open valley is iko s recommended choice and a good up sell opportunity for the roofing professional.
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With a clean valley you can lay down some peel and stick roofing membrane.
