What is valley flashing?
Valley flashing is metal or membrane material installed in the valley where two sloped roof sections meet to direct water runoff downward and prevent leaks at the seam.
Where two roof slopes come together, water naturally collects in the valley between them. Valley flashing is the metal or membrane lining installed in this valley to channel that water safely down and off the roof, preventing it from pooling and leaking into the building below.
Valleys are high-stress areas because they receive concentrated water flow. The flashing must be durable and properly sealed to handle this volume and protect the underlying roof structure and interior framing from rot and water damage.
Two main installation methods exist. Open valley flashing uses a visible metal channel (typically aluminum, galvanized steel, or copper) that carries water between the shingles on both sides. Closed valley flashing is covered entirely by overlapping roof shingles or underlayment, leaving no exposed metal and creating a seamless appearance. Open valleys are simpler to install and shed water more reliably, while closed valleys offer better aesthetics but require more careful shingle alignment to remain watertight.
The specific material and method used depend on the roof pitch, local climate, and building code requirements. In the Hartford area, contractors often choose valley flashing type based on the existing roof system and the building's exposure to heavy rain and ice dam risk. Proper valley installation is critical to roof longevity and is a key inspection point for roof repair providers assessing damage or wear.