I am planning on doing unfaced fiberglass batt insulation over spray foam plus continuous polyiso on the exterior of a small new house. The building code (R316.4) requires thermal barriers between the interior useable space and foam insulation and the prescribed way of meeting that is 1/2" gyp board. I was hoping to do wood interior walls and ceilings - plank, OSB or even metal and not do any gyp board. Does any one know of any test reports that I can give the building inspector that shows that an ignition barrier (OSB etc.) plus the noncombustible fiberglass meets the intent of the building code?
Its not uncommon for a plank ceiling to be installed on a cathedral ceiling and if you have rigid insulation above the sheathing then it does not meet code!