Are Thicker Vapor Barriers Always Best?

Vapor barriers come in varying thicknesses which range from 6-mil to 20-mil, and each thickness has certain benefits and drawbacks to consider. It is generally accepted that vapor barriers under 10-mil in thickness are only effective for short-term use.  

Thin Barriers Tear More Easily 

While thin vapor barriers perform the same basic function as thicker barriers, it is generally accepted that they are less effective in this function than thicker barriers are. This is partly because of their delicate nature. Barriers under 10-mil in thickness are far less resistant to tearing and punctures as a result of pressure, pulling, and sharp objects, for example.  

Likewise, some thin vapor barriers may actually be permeable to a certain degree. This means that while they would prevent the majority of water and gaseous moisture from passing, thin vapor barriers might let small amounts of water into a home even if they are undamaged. Barriers under 10-mil may instead be considered vapor retarders, therefore, and will increase the risk of dampness, humidity, and other issues in your home.  

Thick and Reinforced Barriers Have Many Benefit  

Increasing thickness is not the only way to make a vapor barrier more effective, of course, but thicker barriers are generally more robust and impermeable. Barriers of 16-mil or more generally have a permeance rate of 0.0015 or less, which means they are considered fully impermeable by the standard of American building codes.  

The way in which vapor barriers are constructed also has an impact on their effectiveness, however. Barriers which are constructed with a woven pattern, or which have reinforcing fibers in them will be less prone to tearing and ripping, for example. Likewise, vapor barriers which have some sort of antimicrobial coating will contribute to a lower risk of fungal growths and formations inside a crawl space, even if moisture does somehow gain entry.