http://www.insulation4less.com/
I just bought a roll of insulation for the bus, from the above link..........They recomend having an airspace of at least 3/4".
My ? is, I have large amount of ceiling tile about 1.1/2" thick fiberglass, aluminum foil one side fabric on the other side. If I stuff this AND the 1/4 " new insulation into the bus frame (sides above deck) can I consider the FIBERGLASS as air space???...........TIA Ken.
It's not the same thing. The foil insulation works because of its reflectivity. It needs to be able to reflect the heat "somewhere" hence the airspace. I would be particular about not following the manufacturers instructions implicitly in using this stuff.