Condensation and Radiant Barriers
For an attic space, our recommended installation method for radiant barriers is stapled to the underside of the roof rafters. If you choose to install over the attic floor, keep in mind that condensation may form under a perforated radiant barrier based on sudden extreme temperature differences between the air below the barrier and above the barrier typically found in colder climates in the winter.
If you do stumble across condensation underneath your perforated radiant barrier, you can pull back a few sections of the barrier to increase the air flow to the underside of the barrier to help your ventilation system carry out the moisture.
*** The following text is excerpted from the Oak Ridge National Laboratory Radiant Barrier study.
Preventing Moisture Issues
One precaution for preventing potential moisture problems is the use of perforated or naturally permeable radiant barriers. The higher the perm rating, the less potential for problems. Avoiding high indoor relative humidity, sealing cracks and air leaks in the ceiling, using a vapor retarder below the attic insulation, and providing for adequate attic ventilation are additional precautions.