Open Valley: Method of valley construction in which shingles on both sides of the valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley. Valley flashing is exposed.
Open Valley: A valley where both sides of the roof are trimmed back from the centreline to expose the valley flashing material beneath.
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Open valleys are relatively easy to fix with just a few simple tools like these:
Sheet metal
Wire brush
Metal shears
Roof cement
Trowel ...
Open valleys create a channel for water to flow through. Closed valleys are shingled over completely. The valley is the most vulnerable section of a roof, so do not step on it as you work.
OPEN VALLEY: roof valley where shingles do not cross the valley intersection; flashing does.
PARAPET: a low wall or barrier at the edge of a balcony or roof.
In an open valley, the flashing, which may be made of zinc, copper, or aluminum, is laid in a continuous strip, extending 12 to 18 inches on each side of the valley, while the tiles or slates do not come within 4 to 6 inches of it.
With an open valley, you will want at least a 10" wide strip of flashing running all the way up the valley. The shingles then end about two inches from the center of the valley on either side.
 See also: Shingle, Flashing, Roofing, Roof, Shingles
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