Yes metal roofs are placed directly to the plywood over icynene insulated roof sheathing thats how i always had it done and warranteed.
Metal roofing directly on plywood.
Inspect the plywood for damaged areas.
How to apply metal roofing over plywood step 1.
In reading online it seems wise to install a vapor barrier over the plywood to prevent condensation from getting adsorbed into the plywood from the steel roof.
Sweep the plywood clean of all dirt and debris with a push broom.
Hi todd i have a pole barn design structure that had been turned into a livable dwelling with cathedral ceilings using rigid foam between the metal roof and the ceiling sheetrock i am redoing this and putting a decking down with tyvek protec 200 and then reattaching the metal roof and adding circular pest resistant soffit vents at the end rafters of the roof between purlins for ventilation.
Repair any rotted sections of plywood before installing the metal panels.
In a barn shop or other outbuilding you can attach your metal roof directly to the purlins.
Remove all unused vents pipes and protrusions.
Considering when to.
Also there are numerous better underlayment products as mentioned above including grace products and a host of others all better than felt.
But it seems the condensation will affect the 2x4 strapping.
Be sure the larger edge is laid so that the small edge of the next panel will overlap it.
For many applications a layer of plywood underneath your metal roofing is an unnecessary expense.
Place the first screw.
Install the roofing screws vertically along each rib in the panel.