Can you overlap metal roofing, and by how much?

Side laps

Ribbed panels are made with an overlapping rib on one edge. The next panel's edge sits over it, and fasteners and sometimes stitch screws hold the two together. Many profiles include an anti-siphon channel in the lap so water cannot wick sideways between the sheets. On lower slopes, manufacturers often call for sealant tape in the side lap too.

End laps

• The upper panel always laps over the lower one, like shingles, so water runs over the joint rather than into it.
• The lap should land over a purlin or solid support so it can be fastened through both layers.
• Sealant tape goes between the panels, and the panel maker specifies the minimum overlap, commonly 6 inches or more and more on low slopes.

Direction matters

Installers usually start at the end of the roof away from the prevailing wind, so wind blows across the laps rather than into them. Reversed laps are a common leak source on barns and porches.

Common mistakes

• No sealant on laps of low-slope roofs.
• Overdriven screws that crush the washer, or underdriven ones that leave it loose.
• Mixing panel profiles that do not nest tightly.
• End laps floating between supports.

The code side

The residential code ties lap type to slope: lapped seams without sealant need at least 3/12, while sealed laps can go as low as one half inch per foot. More on choosing metal in metal roofing in Georgia, and on tracing drips in common causes of roof leaks.