Proper installation over a 'cold roof'

I have a log cabin built from an Amish kit. The interior ceilings are open to the rafters - above which is wooden planking, and foam panels. I'm planning to replace the asphalt shingles with an exposed fastener metal roof. One asphalt roofer said the warranty of the shingles might be voided because the cabin is unvented, so I want to make sure the metal roof installation accommodates this unvented 'cold roof'.

Thank you - other than applying wooden strips (not sure of the right term) across the rigid Styrofoam panels to accept the metal roofing, is there anything else we can do to improve insulation or roof longevity? I guess I'm still looking for any guidance about the best way to install over a cold roof.

It's so nice that you offer this Q&A - I've read through most of the threads and have learned a lot.

Allison,

The most critical detail to foster roof longevity is to install it correctly. Sounds a bit flippant in terms of response tone, but overwhelmingly, the biggest issue with the accelerated failure of metal in installation. As long as you are using a well regarded manufacturer from a trusted vendor, installation is the biggest issue leading to premature failure.