Valley Calculator

Calculate valley flashing, ice shield, and materials for open, closed, or woven valleys

Get a fast material estimate from valley count and length

Quick presets

valleys
ft

Estimated Materials

0 bundles

0.0 squares • 0 sq ft

PRO

Professional Calculator

Extended parameters for precise calculations

sq ft

Estimated Materials

60 bundles

Roof Area

1,792 sq ft

Squares

17.9

Detailed Breakdown

Roof Area1,792 sq ft
With Waste1,971 sq ft
Roofing Squares17.9
Bundles60
How to Use This Calculator
The Valley Calculator helps you determine the exact materials needed for your roof valleys — one of the most critical areas for water management and leak prevention.

Quick Estimate tab: Enter the number of valleys on your roof, their average length, and your preferred valley method (open metal, closed-cut, or woven). The calculator tells you how many linear feet of valley metal and ice & water shield to buy. This is the fastest way to add valley materials to your order.

Detailed tab: Specify the valley method, metal type (galvanized, aluminum, painted aluminum, or copper), ice shield coverage, and open valley width. The calculator produces exact quantities for valley metal, ice & water shield, and fasteners. Use this when you have finalized your valley specification and want a precise material list.

Cost Estimate tab: Enter your valley details, metal type, and state. The calculator shows the cost of valley metal, ice & water shield, and installation labor. Valley installation is typically priced per linear foot and may be included in the overall roofing bid or broken out separately for complex roofs.

The Formula
The valley material calculation uses these formulas:

Total Valley Length = Number of Valleys × Average Valley Length For 2 valleys at 16 ft each: 2 × 16 = 32 linear feet

Valley Metal (Open Valley): Metal pieces = Total Valley Length × (1 + Waste%) / Piece Length 32 × 1.10 / 8 ft per piece = 4.4 -> 5 pieces of 8-ft valley metal

Ice & Water Shield: Ice shield length = Total Valley Length × (1 + Waste%) 32 × 1.10 = 35.2 lin ft Rolls needed = 35.2 / 75 ft per roll = 0.47 -> 1 roll (75 ft × 36" wide)

Metal Cost (Aluminum): 5 pieces × $85 per 8-ft piece = $425 Or: 32 lin ft × $13/lin ft = $416

Total Valley Cost (Installed): Metal: $425 + Ice shield: $150 + Labor (32 ft × $12/ft): $384 = $959
Example Calculation
Example: Home with 2 Valleys in Minnesota

Karen is replacing the roof on her 1,800 sq ft home in Minneapolis. The roof has 2 valleys, each about 16 feet long. She lives in a cold climate with significant snow, so she wants the best valley protection.

Step 1: Choose valley method Given the heavy snow and ice dam risk, Karen selects an open metal valley with aluminum flashing and full ice & water shield coverage.

Step 2: Calculate valley metal Total valley length: 2 × 16 = 32 linear feet With 10% waste: 32 × 1.10 = 35.2 ft Aluminum valley metal (8-ft pieces): 35.2 / 8 = 4.4 -> 5 pieces at $85 each = $425

Step 3: Calculate ice & water shield Full width coverage (36" each side): 32 ft × 6 ft wide = 192 sq ft Ice & water shield: 1 roll (75 ft × 3 ft = 225 sq ft) = $165

Step 4: Estimate installation Valley metal installation: 32 ft × $12/ft = $384 Ice shield installation: 32 ft × $4/ft = $128

Total valley cost:
• Valley metal: $425
• Ice & water shield: $165
• Installation labor: $512
• Total: ~$1,102 for 2 valleys
• Per valley: ~$551

Frequently Asked Questions

Which valley method is best: open, closed-cut, or woven?
Open metal valleys are the best for performance and longevity. They handle high water volume, resist ice dams, are easy to inspect and repair, and last as long as the metal (30-100+ years depending on material). Closed-cut valleys are the most popular among residential roofers because they are faster to install and give a clean look, but the cut shingles in the valley can wear faster. Woven (laced) valleys are the cheapest and fastest but are not recommended by most shingle manufacturers — they trap debris, are hard to repair, and look uneven. For any roof with significant rainfall or snow, open metal is the gold standard.
Do I need ice & water shield in the valley?
Yes, in almost all cases. The IRC (International Residential Code) requires ice barrier (ice & water shield) in valleys in areas where the mean daily January temperature is 25°F or below. But even in warm climates, valleys concentrate massive amounts of water flow and are the most leak-prone area of any roof. Best practice is to install a 36-inch-wide strip of ice & water shield centered in the valley, extending 18 inches up each roof plane. For open metal valleys, the ice shield goes under the metal. For closed-cut and woven valleys, the ice shield goes under the shingles. A single 75-foot roll of ice & water shield costs $120-180 in 2026 and covers about 4-5 standard valleys.
How much does valley flashing cost?
Valley flashing costs depend on the material and method. Galvanized steel valley metal: $8-12 per linear foot installed. Aluminum valley metal: $10-16 per linear foot installed. Painted aluminum: $14-20 per linear foot. Copper 16 oz: $30-50 per linear foot. Copper 20 oz: $45-70 per linear foot. For a typical home with 2 valleys at 16 feet each (32 total linear feet), aluminum valley flashing costs $320-512 installed. Add $120-180 for ice & water shield underneath. Closed-cut and woven valleys skip the metal but still need the ice shield.
How do I prevent ice dams in roof valleys?
Roof valleys are the most common location for ice dam damage. Prevent ice dams in valleys with these strategies: (1) Install ice & water shield the full length of every valley, extending 18"+ up each plane; (2) Use open metal valleys, which shed ice and water better than closed or woven; (3) Ensure proper attic insulation (R-49+ in cold climates) and ventilation to keep the roof deck cold; (4) Install heating cables in valleys as a last resort in extreme cases; (5) Keep valleys clear of debris (leaves, needles) that trap moisture and ice. The most effective combination is proper insulation + ventilation + ice shield + open metal valley.
How wide should an open valley be?
The standard open valley width is 6 inches of exposed metal at the top, widening at a rate of 1/8 inch per foot toward the eave. For a 16-foot valley, the top would be 6 inches and the bottom would be 8 inches (6 + 16 × 0.125). This widening prevents debris from damming near the bottom where water volume is highest. High-flow valleys — where large roof planes drain into the valley — should start at 8-10 inches. The total metal width (including the portion under the shingles) should be at least 24 inches (12 inches on each side of center). Some codes require W-metal valleys that have a center crimp to prevent cross-wash.

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