Valley Flashing Calculator
Calculate valley flashing requirements for roofing projects. Supports open, closed, and woven valley types with multiple material options.
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How Valley Calculation Works
Total Length = Valley Length × Number × Overlap Factor
Calculate total valley length with overlaps
Material Sq Ft = Total Length × Width
Convert linear feet to square footage
Fasteners = Total Length ÷ Nailing Pattern OC × 2
Calculate nails for both sides
Valley flashing is installed in the valley where two roof planes meet. The calculation accounts for the valley length, number of valleys, and overlap requirements.
Open Valley: Uses full valley length + 12" overlap at joints.
Closed/Woven: Uses 75% of length (shingles cut to valley).
Reference: ARMA Asphalt Roofing Manufacturers Association
Frequently Asked Questions
W-Valley (twisted) has a twisted edge that spreads out to center the water flow, ideal for most applications. V-Valley (flat) is a flat piece that folds into a V shape, more traditional but requires careful installation.
Standard practice is 12 inches minimum overlap at all joints. For longer valleys, increase overlap to 18-24 inches for better water protection.
Standard is 12 inches on-center along both edges, keeping nails 2 inches from the valley center. Heavy nailing (6" OC) is recommended for high-wind areas.
Open valley is generally recommended as it performs better long-term, allowing water and debris to flow freely. Closed valley (shingles cut to valley) can trap debris and may have shorter lifespan in harsh climates.
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