perpetualjon

The illustration within this article is only half the story as we go from a winter to summer situation. This process of causing condensation by hitting the dew point can occur in either direction so the idea of creating a vapor barrier out of a single layer of poly sheeting should be actually on BOTH sides of the insulation layer. This is why using spray polyurethane foam is so much better. It creates a vapor barrier on both sides of the insulation material naturally so it will prevent condensation forming in either direction. Yet another reason why foam insulation is worth the extra expense.