Roofing Glossary

Valley Flashing

Valley flashing is the waterproof lining installed in a roof valley before the shingles go on — typically galvanized steel, aluminum, or copper, or a self-adhering membrane. It is the valley's last line of defense: if water gets past the shingles, the flashing carries it down and off the roof.

In an open valley, the metal flashing is left visible as a clean channel down the valley center, with shingles cut back on each side. In closed or woven valleys, the flashing is hidden beneath the shingles but still does the same backup work.

Valley flashing must be wide enough — typically 24 inches — and free of fasteners in the center water channel. Nails through the middle of a valley are a built-in leak.

Why It Matters

Valleys concentrate more water than anywhere else on the roof, so the flashing beneath them works harder than any other flashing. During a roof replacement, new valley flashing is non-negotiable.

Questions about your own roof? Request a free estimate or call Nucci Brothers Roofing at (301) 458-1003.