Experts advise builders against the installation of an interior polyethylene vapor barrier unless they are building in a very cold climate — for example, in the colder regions of Canada and Alaska.

Radiant Barrier Moisture Problems The other main issue that can impact the performance of any radiant barrier is moisture. In colder weather, radiant barriers can sometimes develop condensation. This issue is most prevalent in climates where the temperature regularly falls below zero degrees Fahrenheit.

Between the insulation and the sheetrock I staple 6 mil plastic; I was taught this a few years ago, and it seemed to make sense (as I recall, the reasoning was the the plastic forms a vapor barrier, which keeps interior moisture from getting “trapped” in the insulated walls).

Some studies show that radiant barriers can reduce cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it's usually more cost-effective to install more thermal insulation than to add a radiant barrier.