James writes from Round Rock, Texas: "I am finishing a small attic space (not the "main" attic. I have 2x6 rafters and want to get as much insulation as possible without having to build them out. My question is as follows: Can I install a radiant barrier directly to the roof decking between the rafters, then install R19 and then install foam board over that before adding the sheetrock. Will there be enough space for air flow? Does the radiant barrier have any impact?"

Answer: Fiberglas™ R-19 insulation is 6-1/4" and will fill that 5-1/2" cavity and more. There will be no space for the recommended 1" airspace under the roof deck. Owens Corning does not manufacture radiant barriers, and has no recommendations related to their use. You may want to contact a company that produces them to find out more about their use.