Do we even really need vapor barriers? Matt Risinger noticed that a lot of the builders he came across were using vapor barriers incorrectly, and they kept asking him when, and if, it was necessary to use them. Humid air diffuses through a wall and holds where it is warmer, such as a heated home in the winter. Places like the Northeast might benefit from an interior vapor barrier, whereas warmer places like Texas and Florida would benefit from an exterior vapor barrier to prevent humidity from getting inside. It all comes down to science at the end of the day. We find out that diffusion through sheet rock is pretty slow though. During a heating season you may diffuse 1/3 of a quart of water only. What does this mean? And what does this mean in terms of vapor barrier necessity? Watch the full video to find out.