Acceptable fasteners include plated self-drilling wood screws or galvanized nails. Nails should be spiral or ring shank design with a neoprene gasketing under the head.
Wood screws with combination metal and neoprene washers should be mechanically driven into the valley or the bottom flat of the profile. See Figure 1.
Screw length should allow a penetration of 1 inch. When installing panels over insulation board, increase the above length by the amount of insulation thickness. Select nail lengths for roofing and siding that do not completely penetrate through purling or girts.
The correct way to nail is to drive the fastener through the steel so the nail washer is compressed securely against the metal. however, DO NOT OVER-DRIVE the nail and dimple the steel. If this is done, water may collect in the dimpled area and leak through. Under driving can also allow leakage to occur around the nail shaft.
Never drive screws or nails through the drain channel, as the result may cause leakage and ruin the effectiveness of the drain channel.
Industry standards are that:
screw fasteners be applied in
the flat next to each major rib on both roof and side walls, and
nails be applied through the ribs on roof and through the flat on side walls.