Valley (roof flashing)

Definition: A valley in roofing refers to the internal angle formed where two sloping roof surfaces meet. This area of the roof is critical for directing water flow, channeling rainwater and snowmelt off the roof and into the gutter system or other drainage points. Valleys are essential in preventing water buildup on the roof, which can lead to leaks and damage. Due to their function and position, accessories handle the highest concentration of water runoff, making them vulnerable to leaks if not properly installed or maintained.

Types of Roof Valley:

• Open: An open valley features exposed metal flashing running along the seam where the two roof planes intersect. The roofing material, such as shingles, is cut back from the centerline, leaving the metal flashing visible. This type is commonly used in areas with heavy rainfall or snow, as the exposed metal provides a durable, efficient way for water to flow off the roof.
• Closed: In a closed type, the shingles from both roof planes extend across the valley, overlapping each other and covering the intersection area. There are no visible metal components, making this a more aesthetically pleasing option for homeowners who want a seamless look. However, closed valleys may not be as durable in areas with high water flow or heavy snow, as the shingles alone must handle the runoff.
• Woven: A woven type involves interweaving the shingles from each roof plane, creating a continuous surface over the roof intersection. This type is commonly used with asphalt shingles and is labor-intensive to install. While it offers a uniform appearance, woven flashing may trap debris or water if not properly constructed, leading to leaks or damage over time.

Materials Used in Valleys:

• Metal Flashing: For open valleys, metal flashing, often made from materials like galvanized steel, aluminum, or copper, is used to line the valley. Metal is durable, long-lasting, and effective at channeling water away from the roof. Copper is often preferred for high-end homes due to its appearance and ability to resist corrosion.
• Shingles: In closed and woven components, shingles themselves form the protective layer over the roof intersection. These shingles must be carefully installed to ensure water flows properly off the roof and does not seep beneath the roofing material.
• Ice and Water Shield: A common addition beneath valley installations is an ice and water shield, a self-adhering waterproof membrane. This layer provides extra protection against water infiltration, especially in colder climates where ice dams or heavy snow can increase the risk of leaks.

Importance of Proper Installation:

• Water Flow Management: Valleys handle significant water flow from multiple roof planes, making them one of the most critical areas of the roof. If improperly installed, they can lead to water pooling, which can seep into the roof deck and cause leaks, wood rot, or mold growth.
• Debris Accumulation: They often collect leaves, twigs, and other debris, especially in regions with overhanging trees. This debris can block water flow and lead to water buildup. Regular maintenance, such as cleaning seams, is crucial to ensuring the roof remains leak-free.

Common Problems in Roof Valleys:

• Leakage: If they are not installed correctly, water can seep under the roofing material, leading to leaks.
• Shingle Deterioration: Shingles can wear out faster due to the concentrated water flow, increasing the risk of damage over time.
• Ice Dams: In colder climates, ice dams can form in the flashings, preventing water from draining properly and increasing the risk of leaks or structural damage.