1. Using plywood or OSB sheathing, attach sheets perpendicular to the roof joists. Your nails should be the galvanized or stainless steel type.
2. Roll out building paper over the sheathing, overlapping each row about half a foot (6 inches). This will help form a moisture barrier. Although you can use nails to secure the paper, staples are much faster and do the job just fine.
3. Over the building paper, Install sheets of rigid foam insulation over the entire roof surface. Butt the sheets closely together, staggering the seams between rows, and don’t overlap.
4. Tape all the seams with 3-inch weatherproofing tape. Apply silicone caulk to the edges, where the insulation meets the flashing. This will help prevent air leaks and maximize the insulating ability of the roof. Allow the caulk to dry at least eight hours before installing metal roofing.
5. Now you are ready to install the metal roofing panels over the insulation. Be sure to follow the manufacturer’s installation instructions.
The foam insulation will make a huge difference in your overall heating/cooling costs for the building.