Roof materials
Valley flashing calculator
Estimate valley flashing length. Roof with open or closed valleys.
Try the calculation
Add valley runs and round up to product lengths.
Adjustable example. Change these illustrative inputs to match your task, then recalculate. Reset restores the example and its result.
Understand the result
How this calculation works
Valley flashing quantity is based on the total measured valley run.
Steps
- Enter one or two valley lengths and the coverage of one piece.
- Leave the second valley blank when unused.
The form starts with the worked example below. Change its values and selections to match your task; Reset restores the example.
Formula
pieces = ceiling((valley 1 + valley 2) รท piece length).
Variables and units
- Valley 1 (ft)
- Required. Use a positive value. Starting example: 24. Replace it for your task.
- Valley 2 (ft)
- Optional; blank contributes zero. Zero is accepted. Starting example: 16. Replace it for your task. Leave blank if there is one valley.
- Piece length (ft)
- Required. Use a positive value. Starting example: 10. Replace it for your task.
What the result means
This rounds stock pieces for the entered runs. It does not set valley width or installation details.
Worked example
Inputs: Valley 1 = 24; Valley 2 = 16; Piece length = 10.
Calculation: 24 ft + 16 ft = 40 ft; at 10 ft per piece, 4 pieces are required.
Result: 4 pieces.
Frequently asked questions
Can I leave Valley 2 blank?
Yes, one valley is a valid input path.
Does it calculate sheet cuts?
No, it uses the entered piece length only.
Should laps be added?
Use effective coverage after any product-specific overlap.