Plastic vapor barrier under house

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Old 11-03-10, 08:04 PM
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Question Plastic vapor barrier under house

I removed the plastic vapor barrier from under my house because I had a leak in my pool drainage line going to the sewer which flooded under my house.

I let it dry out the best I could and had a exterminating company install new plastic under the house.

About a foot around the edge next to the foundation does not have plastic installed. They said this would allow the moisture to come out and go back into the ground.

The exterminator who installed the original barrier did not leave this empty space but covered tje ground completely.

Who is correct and should I have them fix it? They said they would if I wanted it to cover all the way.

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Old 11-04-10, 11:12 AM
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Actually, none of these approaches is 100% effective to control moisture in the crawl space.

If you leave part of the ground uncovered, you are still allowing some level of ground moisture to evaporate into the crawl space. That, will cause the RH to go up and water will condensate all over the place, favor mold growth and rot.

If you cover all the ground with a vapor barrier, you are addressing ground moisture and preventing it from evaporating into the crawl space.

However, crawl spaces get moisture from more than just the ground. The outside air, which also carries some moisture during warmer months, is still getting into the crawl space through vents (and even if you close the events) through openings.
When that air comes in, the difference in temperatures between the outside and the crawl space, will cause the RH in the air to nearly double.

So the water will condensate on the surfaces, wood will soak it up, mold and rot will develop.

If you really want to protect your crawl space and preserve the structural integrity of your home's foundations, you will need to have your crawl space fully encapsulated.

That means, entirely lined with a sturdy vapor barrier, completely isolated from ground and outside air, and conditioned by means of a crawl space conditioning system or a dehumidifier.

Several studies, conducted by reputable organizations (Advanced Energy, Building Science Corp., Habitat for Humanity), conclude that encapsulation is not only the only effective method to control moisture, but it also increases a home's energy efficiency an average of 18% and significantly cuts energy losses.

Encapsulation is also the method recommended by the U.S. Department of Energy and the Green Building Council. I suggest you take a look into it. Here's an article with several links on the subject.

Crawl Space Encapsulation
 
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