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Vapor Retarder Thickness Considerations

Posted by Nana Hinsley on Mon, Feb 07, 2011 @ 12:29

Question: My house is built on a crawl space, like most of the houses in my area. Only part of the dirt floor of the space is covered with plastic. Do I need this plastic cover and if so, what thickness do you recommend?

Answer: Ideally you should cover the entire floor and the walls with a high performance vapor retarder. This is called encapsulating the crawlspace and offers a good number of benefits. The #1 reason so many people are doing this is to reduce - moisture transmission, mold, and mildew. Radon is also a huge problem in many parts of our country, and installing an encapsulation significantly reduces the amount of the odorless, colorless gas that is the second leading cause of lung cancer in the USA today. Our company highly recommends engineered vapor retarders for this application, rather than using low grade construction plastic like is normally sold in home centers. The performance differences are quite substantial. For one thing our liners made for use as crawlspace liners will not degrade when in contact with soil. Construction/Agricultural Grade Poly will often degrade within 2-3 years. Our products will last indefinitely under the same conditions where the lower grade products will degrade. Above, I mentioned that the walls should also be covered. One should try to go far enough up the wall that the liner is above ground level, where it should be securely sealed to the foundation wall. This gives the gases and moisture a much easier path to the outdoors, through the block or concrete. One should stop short of attaching the plastic sheeting to the wooden joists under the home. This is necessary for bug inspections, plus keeps the moisture from being transferred into the wood.

Tags: vapor retarder, Thickness for Vapor Retarder, encapsulation, crawlspace plastic