Because a vapor barrier is a low permeable barrier, it keeps moisture from passing through. This is beneficial to keep moisture away from a dry surface but will trap moisture behind it if installed on a water-damaged concrete wall, causing the wall to fail further.

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.

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.

You should always install a vapor barrier to protect exposed ceiling insulation even if it's temporary. Consult with a building or safety expert to confirm where else in the structure a vapor barrier may be required.