Metal panel length — horizontal run × pitch factor + eave overhang
Panel length = horizontal run × pitch factor + overhang. A 4:12 slope over a 15-ft run makes a 15.81-ft slope run → order 16-ft panels. Standing seam runs one continuous piece; exposed-fastener panels end-lap over support only when the run beats the stock length.
What this diagram shows
A roof-plane cross-section drawn as a right triangle. The 15-foot horizontal run along the bottom is multiplied by the NRCA pitch factor for a 4:12 slope, 1.054 (the square root of 4 squared plus 12 squared, divided by 12), to give a slope run of 15.81 feet measured along the panel. Adding a 1-1/2 inch eave overhang gives the finished length, rounded up to a 16-foot order. A note contrasts the two systems: standing-seam panels run as one continuous eave-to-ridge piece up to about a 52-foot factory maximum with no end lap, while exposed-fastener panels that exceed the stock length take a 6-inch minimum end lap positioned over solid support and sealed with butyl.
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