Vapor Barrier is listed here as an option in the marketplace yet it is really a necessity as part of any crawlspace moisture solution including the ATMOX System in almost every situation. Having a ground vapor retarder is outlined in building code requirements for wall vented crawl spaces.
Yet, there are many questions regarding vapor barriers. The questions include: How much coverage? What thickness of plastic? Should seams be taped? Should plastic be nailed? Should plastic be on the walls? Just as there are many questions, there are just as many opinions on how vapor barriers should be installed. ATMOX is hereby offering another opinion, as unbiased as possible, particularly as it relates to use with an ATMOX system. ATMOX believes in doing what is necessary without going overboard.
The purpose of the vapor barrier is to suppress moisture coming up from the ground. The vapor barrier will not eliminate all moisture, but it will serve as a time-release mechanism to control the moisture as it comes into the crawl space. For a vented crawlspace or an ATMOX controlled crawlspace, it is not necessary to eliminate all moisture release. The goal is slow the release of ground moisture into the air so that the natural airflow and the ATMOX system and fans can adequately dissipate the moisture out of the crawlspace. For a closed or conditioned crawlspace, the vapor barrier will need to be completely sealed and taped to work properly to control the moisture.
The more humid the climate is, the more important the vapor barrier coverage is. Our general recommendation is to have 100% coverage of the crawl space floor with seams overlapped at least 12 inches. Unless a crawlspace is very high and easy to navigate, the seams should be either staked, taped or sealed down with adhesive. If using stakes, then use as few as possible to hold the plastic in place as in the future if the plastic is moved those stakes can create holes or moisture release points. The goal is to keep the plastic in place as homeowners, workers, contractors or inspectors go into the crawl space to work. If the plastic doesn’t have enough overlap or isn’t kept in place, it will shift over time losing its coverage over the dirt. In general, the plastic only needs to go up the wall about 4-6 inches unless you have a wall that is below grade and seeping water. It is important to talk to your pest control company about this as many pest control companies will void a termite warranty if they cannot pull the plastic back in order to inspect the area where the ground and block meet. (Termite warranties can be an issue with closed or sealed crawlspaces depending on your provider.)
Plastic used in vapor barriers is measured in its thickness and ranges from 4 mil plastic up to 20 mil plastic. The lower the number (or the smaller mil) is the thinner the plastic is. For the most part, any thickness of plastic will stop the release of moisture in the area that it is covering. The problem with plastic that is too thin is that it easily get damaged by people going into the crawlspace after it is put down. Then when the plastic gets disturbed or ripped, it leaves gaps creating areas for moisture release. On the other end of the spectrum, plastic that is very thick and heavy can be difficult to work with and is expensive. You can really use any thickness of vapor barrier. Our recommendation is the 6-12 mil range with preference for the 10 mil thickness. This mid-range is a nice balance of thickness, durability, cost and performance.