Insulating after metal roof install on older building

I may not have been clear before the installation of the metal roof this building had a conventional roof where Tongue and groove boards were nailed to the trusses and then tar paper and shingles applied on the outside from there. Inside they used prop a vent and fiberglass insulation with a ridegevent.. Now metal has been applied with it's own ridge vent and venting for the metal is done by the rigid contours of the metal and a metal ridge vent. I want to now go inside and finish that area off where I can access some I cannot access. I want to strip the fiberglass insulation and spray foam in it's place but I cannot get to every space between every truss and sometimes I cannot get down to the soffit area on the inside either due to different roof angles and access. The original roof used a ridge vent and soffit vents with prop a vents. I do not understand what you mean when you say "I would recommend the installation of some rigid foam prior to install the spray foam. This will allow you to remove the roof if it ever required service without having to destroy the foam."

I have a log home about 25 years old. Recently installed a metal roof some after stripping to boards and installing Ice and water shield on entire surface and some was installed over existing shingles as it was not as old as other. Installation of metal roof was done by the Amish and they installed strapping and foam panels and then taped all seams and then installed the metal with a ridge cap. I am now wanting to finish off the attic area loft which has old fiberglass insulation that has animal smell in it and I want to remove as much of that as possible and replace by spraying foam in all rafter spaces that are accessible. I need to know if I need to worry about any ventilation in those areas where the foam is to be installed and what should do in any areas that I cannot get to with the spray foam. I should add this will leave runs where the old fiberglass will have to remain. I cannot get to every space in between rafters. Is the air vent in these original fiberglass insulation areas still in use with the metal installed or has the metal and it's venting taken over for any previous venting done on the structure? Thank you

If you cannot access the soffit or enough so that you can seal them off and create a truly unvented attic application, I would suggest that you leave some sort of vented space below the roof. In this application, I would plan on ripping down strips of foam to created a vented space (ideally 2") between the roof deck and the rigid foam that you will install in the rafter bays prior to spray foaming. There are some good pictures in this article that will help illustrate this point. If you can't completely seal it off, you need to vent it. You can go half vented, and half unvented. http://www.finehomebuilding.com/how-to/articles/a-crash-course-in-roof-venting.aspx