I have a question about the effectiveness of applying a sheet of aluminum radiant barrier beneath 1/2″ plywood or OSB decking on which either 30# tarpaper felt and a 30-year composition roof would be placed or a layer of titanium synthetic felt and a metal roof would be put. The aluminum side on this sheathing material would face towards the attic. Would the radiant barrier work for either of these conditions? If not or if there is a better option, could you explain what should be done? I have earlier read that there needs to be a 3/4″ of air space to be present for the radiant barrier to function effectively.
I will shortly be constructing a building that I would like to use radiant barrier to reflect some of the South Texas heat from the interior of this building. I am also considering using some of the radiant barrier in conjunction with 1/2″ plywood sheets that have hardened wooden surfaces for the walls of this structure. Should the radiant barrier be placed directly on this plywood or should it be first attached to the wooden studs and then the plywood sheets be placed on top of it?
The general rule for a radiant barrier installation is that the reflective side should face the large open space of the interior of the building — like in the attic of a house. You can encapsulate it in a wall or ceiling cavity so long as the reflective side looks at an air space of at least 3/4”. However, on a hot day in TX, that air space is likely to heat up pretty fast and then the heat will transfer into the interior of the building. If the radiant barrier is installed facing the open space, the air temperature in the attic should not get any higher than the outside ambient air temperature.