Update explanation: there is a second story with insulated attic space on the sides and a vaulted ceiling.
I have a dual issue. I have standing seam metal awaiting installation and have ordered 3 1/2" of hard foam insulation to add to my 1920's skip sheathing. I plan to add 1/2" sheathing atop the foam and attach with long screws. I will surround this with 2x4 trip to shim the roof up. The ventilation will occur at the skip sheathing layer. I'm opting to avoid adding 2x4 rafters to attach the plywood, so as to create a continuous insulation layer.
The second issue that concerns me is that little ants have been attacking the hard blue foam insulation in the walls of my old shop leaving piles of blue dust. I finally had to spray them, but I have heard they like formaldehyde....a relative of formic acid?
So as I add a layer of 2"+1 1/2" foam panels to the roof I am concerned about this dietary issue.
If you have any options and info on this I'd be so appreciative. --Ben
Last edited by Ben gilmore; 04-02-2012 at 12:34 PM.