I still get this question all the time. “Can you explain why an air space is needed for a radiant barrier to work?” Watch this video for a complete explanation.
Basically it works this way. Radiant heat is heat that is transferred across either an air space or a vacuum. This is how the heat from the sun reaches the earth. Radiant heat acts similar to a sound wave. By definition, you MUST have either an air space or a void for radiant heat to even exist.
If you don’t have an air space then you basically have a solid. Heat can essentially only move through a solid by conduction. This is by direct contact. This is how an egg cooks on a hot skillet.
So, without an air space, you cannot have radiant heat. Without radiant heat there is no way to have a “Radiant Barrier”. In fact, because of the conductive nature of pure aluminum, if you install radiant barrier foil WITHOUT the required air space it will actually work AGAINST you and INCREASE Heat flow.
The bottom line is you MUST have an air space on one side of a radiant barrier for it to work.
Looking for more videos on this topic? Check out my posts below.