Roofing shingles are installed then cut and sealed where they overlap the metal channel.
Roof valleys metal or shingle.
With an open valley a strip of metal will be visible on the roof wherever two opposing roof planes meet.
For example in metal roofing systems valleys are commonly fabricated with hems but can also be fabricated without them in which case they could still be used for metal roofing or any other type of roofing.
For an open valley a sheet of metal usually steel sometimes copper is fastened to the roof deck.
That flashing is left exposed so the roof has visible lines of metal running down the valley.
A chalk line is then used to strike a line from the top of the valley to the bottom of the valley.
These items can be fabricated in many different profiles.
In addition it is important to avoid nailing the shingles through the valley metal.
The metal is usually pre painted to best complement the shingles color blend.
The shingles are then cut out of the valley area opening the surface of the valley lining to water run off and the environment.