I pulled the cap off my cab tractor just to see what was in there ... well there was no insulation of any kind. So I insulated it by useing 3.5" fibergalss pulled it apart so it was about 1.75" and put a layer over the cab and put the roof cap back on.

Now I'm thinking do you suppose there was none because fan blowers, or any relays up there need to breath? What ya'll think?