vapor barrier or no vapor barrier

Old 01-22-05, 08:32 PM
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vapor barrier or no vapor barrier

I am a little confused...

Many of the posts on this forum (that I have read) discuss the use of a vapor barriers and how much airspace to leave between the 2X4's and foundation.

But the documentation from the US Dept of Energy (link below) recommends not using a vapor barrier and filling the space between the 2X4's and foundation with rigid insulation board.

The US Dept of Energy appears to have alot of research backing-up their why are people still discussing vapor barriers and airspace? Am I missing something?

US Dept link:
Old 01-22-05, 08:59 PM
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Hello: J

By moving your question into the insulation topic, which I have done for you here, you will more likely find the answers in the already existing questions on the subject of vapor barriers and airspace.

To further help you obtain the answer(s) to your question(s) the forum topics moderator resercon will be able to help you futher. If resercon cannot help you, no one can. He is the best in the entire industry, imo.

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Old 01-22-05, 09:00 PM
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I feel your pain.
I was going to do the same thing, but then I read studies from several universities that straight up say that no matter what is done, moisture is a problem.
I think you have to look at your individual situation. There are arguments both ways.
There is one thing everyone agrees on
You should and it is best to install a vapor barrier and insulation on the exterior of the basement, during the build before the backfill.
It the only right way that I have seen so far.
Old 01-23-05, 07:24 PM
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Moisture problems in basements are usually a result of contributing factors.

Standardized building methods have been around for a long time, including the use of dead air spaces and vapor barriers. In fact they will be in use long after we are gone. The percentage of moisture related problems has not increased over the years, it has just been brought to the forefront. Furthermore, the standard building practice by itself was not the cause of the moisture problems, mold or mildew. If that was the case, nearly everyone who has a finished basement would be experiencing mold and mildew problems.

There is a great deal of information on the web. And after seeing many posters refer to sites supporting their comments, I believe it is time for me to say something on this issue. A Hypothesis is best known as an educated guess. Within an industry, it is referred to as conjecture. Thesis is a formal proposition that is advanced and defended through argumentation. Within an industry, it is referred to as substantiated information.

Under the Reagan Administration policy of streamlining government, many of the processes government used to protect consumers were eliminated. A perfect example of its usefulness is the quick approval of the drug AZT for AIDS. A bad example would be Vioxx and Sick Building Syndrome. In the field of energy conservation there are presently two major sources that influence National, State and Local Energy Codes. They are the Building Science Organizations (BSO's) and Laboratories. BSO's are the ones that produce the Hypothesis and the Labs produce the Thesis. Though the BSO's have experiments and other data, it is there to support their Hypothesis, educated guess or conjecture. Far too often these papers are being interpretted as being valid applications. Labs, like Oak Ridge National Laboratory, take the Hypothesis and proves or disproves it through years of experimentation and analysis. At that point they stand before a panel of their peers and defend their position before it becomes a valid application. The data to support their position usually comes in volumes.

I do not want to detract or say anything derogatory about BSO's. Besides the fact that I know quite a few people in these organizations, they are by far extremely dedicated to their profession. And in my opinion their reputations are beyond reproach. It is also my opinion that their work, creativeness and innovation has, is and will advance energy conservation throughout the world. My only concern here is how these papers are being interpretted by lay people.
Old 01-26-05, 08:03 PM
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If you have 2 to 4 inches (ie: R-10 to R-20) of extruded poly styrene fastened flush against the basement wall (no air space) including the exposed top ledge, sealed at the top and bottom, sealed at all joints, and firmly strapped in place, would it be safe to assume you don't need a vapor barrier between it an the drywall? (ie: there is no cold surface to be concerned with condensation). That is the understanding I have, but perhaps there is a flaw in my logic? I *think* this is a much different situation than a 2x4 studded wall with a dead air space between it and the concrete which of course requires vapor barrier.

Further, would vapor barrier behind the drywall cause a problem by trapping moisture between it and the foam? (the moisture that permeates through the foam)

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