Roofing
Valley
The internal angle formed where two roof slopes meet, which concentrates water runoff and requires special waterproofing treatment.
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In the Field
Valleys are the highest-risk area on any roof. Three methods are used: open valley with metal flashing (best for longevity), closed valley (shingles woven together), and closed-cut valley. Open valleys last longest and are easiest to inspect.
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Rule of Thumb
Apply ice and water shield the full length of every valley, extending at least 18 inches on each side. Add metal valley flashing over the ice and water shield for open valleys.