Roofing Installation Sequence
Begin laying the roofing panels on the end of the building away from the prevailing wind so that the side lap seams face away from the prevailing wind-driven rain. This provides extra security against water penetration.
When installing metal panels over green or damp lumber, a positive vapor barrier (builder's felt, wrap, or bituminous paint) must be installed to separate the panel from the wood.
The first panel determines the alignment of all remaining panels on the roof, so extreme care must be taken to accurately square the first sheet. The overlapping rib edge should be flush with the edge of the roof (Figure 1), and the panel should overhang the eave approximately 3 inches to provide for a drip edge. The side rib with the drain channel should face the direction in which the sheets are being laid down (Figure 2). When the panel is positioned, it should be fastened through the first rib, top and bottom. The panel should be attached completely before starting the next panel.
A tip for assuring straight alignment for successive rows of panels is to stretch chalk lines between nails driven into the ridge and end of each edge rafter. These lines will serve as guidelines to align panels.
If a roof requires more than one horizontal row of panels, temporarily fasten at two points, not the ends, along main middle ribs of Panel #1 in lower corner. Next, install Panel #2 above and end lapping over Panel #1. Alilgn both panels with chalk line. Install Panel #3 next to Panel #1 side lapping it. Install Panel #4 above Panel #3 side lapping over Panel #2 and end lapping over Panel #3. Check alignment at ridge and eave again. temporarily fasten all panels; permanently fasten when all panels are in line (see figures 3 and 4 below).