Flashing & coil guide · 6 min read
How to calculate flashing coil stock
Convert flashing height, piece coverage, laps, and wall runs into a piece count and realistic coil-stock requirement.
Separate the lock from the engagement
The width cut across the coil becomes the starting width of each flashing piece. Material used to form an S-lock or receiver no longer advances along the wall, and every following piece loses additional coverage where it engages the previous piece. The first piece can therefore cover more than the repeating pieces.
First coverage = stock width − lock allowance − first-end allowance Repeating coverage = stock width − lock allowance − engagement
Example only: a 36-inch blank with 2 inches used to form the lock, no first-end allowance, and 1 inch inserted into the previous piece covers 34 inches for piece one and 33 inches for every following piece. Those dimensions are profile-specific, not universal.
Calculate a mixed-coverage piece count
Apply the first-piece coverage once. If wall length remains, divide only that remainder by the repeating coverage and round up.
If run ≤ first coverage: 1 piece Otherwise: 1 + round up [(run − first coverage) ÷ repeating coverage]
Calculate coil consumed by each blank
The flashing height is cut along the roll, so a 10-inch-tall straight flashing piece consumes 10 inches of roll length. Multiply that cut length by the piece count for the straight-run total.
Straight roll use = piece count × flashing height
Add allowance after the cut schedule
Build the real piece schedule first, then add allowance for squaring ends, brake setup, damaged coating, test bends, handling, and mistakes. Compare the resulting requirement with the full and partial rolls physically available.
Coil calculations estimate blank material. Confirm the developed profile width, hems, hooks, bends, minimum bend radii, seams, fastening, drainage plane, and compatibility for the actual detail.