I'm in the process of renovating a bedroom on the second floor and I have a few boards of silverboard (a Polyisocyanurate Foam Board Insulation) lying around and would like to use. The exterior wall is brick followed by a spacing followed by another wall (some sort of concrete). Since the silverboard has radiant shielding on both sides and sandwiches a stiff foam board, would I:
1) install the silverboard in contact with concrete wall, or
2) leave a spacing in between the concrete wall and the silverboard?