What is valley flashing?
Valley flashing is the metal or membrane material installed in the valley where two roof slopes meet to direct water runoff and prevent water infiltration.
A roof valley is where two sloped surfaces converge, creating a V-shaped channel that funnels rainwater downward. Valley flashing is the metal or membrane strip placed in this valley to guide water safely to the edge of the roof and prevent it from pooling or seeping under the roofing material. Common materials include galvanized steel, aluminum, copper, or rubberized membranes, depending on the roof type and climate.
Valleys are inherently vulnerable to leaks because water volume concentrates in these channels. Debris, leaves, and ice dams can clog valleys and cause standing water, while expansion and contraction of materials over time can separate flashing from the roof surface. Improper installation, including misaligned overlaps or insufficient slope, creates pathways for water to penetrate the roof deck.
Proper valley flashing must slope at least 0.5 inches per 12 inches of horizontal run to encourage water drainage. The flashing should extend several inches beneath the shingles on both sides and be sealed without gaps. Homeowners in Connecticut should have valleys inspected regularly during roof maintenance cycles, especially after heavy snow or ice events, since freeze-thaw cycles accelerate flashing deterioration. Contractors who specialize in roof repair can assess valley condition and replace compromised flashing before water damage spreads to interior framing or ceilings.