reflective roll insulation over perlins

I have an existing metal roof that I am going to replace. the house was build in the early 1900's and it has log rafters and perlins. Would it be a good idea to put reflective roll insulation over perlins before I put the metal roofing on? Thanks

Radiant barriers require and air gap to work effectively. If they are just under the metal, they serve as a conduit is all.

Can you post up some pictures? There is definitely the opportunity to upgrade the insulation in these cases and you absolutely do want to do that, just with the right stuff.