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Vapor Barrier


rantraca's Avatar
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10-21-02, 06:46 PM   #1  
rantraca
Vapor Barrier

Here's a question someone may be able to answer: Does one need vapor barrier (VDR) below the ground line in a basement?
I have a layer of R12 insulation placed against the cement in my four-foot basement. Does it need a vapor barrier all the way to the ground, or at all?
The climate is cold here (Alberta, Canada).

Thanks.

 
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10-21-02, 07:47 PM   #2  
A vapour barrier is a poly membrane placed on the warm side of the insulation. Its function is to stop warm, moist interior air from entering the wall cavity then cooling & condensing which will dampen & reduce the R value of the insulation. The vapour barrier is not to be confused with the "MOISTURE BARRIER" The moisture barrier is to be placed next to the foundation wall before furring or insulation from the bottom of the floor joist to the basement floor. Its purpose is to prevent moisture migrating through the foundation walls due to soil pressure, contacting the insulation causing it to become wet & reducing the insulation value.

 
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10-22-02, 08:28 PM   #3  
rantraca
Thanks for the reply.
I'm not confusing the two but perhaps presented my post on the vague side. I am wondering if one needs to bring the vapor barrier (placed on the insulaion) right to the floor or is it allowable to leave an opening of say 18 inches from the floor.
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10-25-02, 03:09 AM   #4  
If the wall is insulated full height (less 6" from floor in case of minor flooding) the vapour barrier should be from the top wall plate to bottom plate sealed with caulking at ends and over lapping joints. If left open it reduces the effectivness of the barrier. If the insulation is only on the top 4' of wall, apply blocking between studs where the insulation stops and vapour barrier to the blocking & seal. Insulating the top 4' is minimum code requirements, Less heat is lost through the wall below this level. However, having lived in Alberta myself I know the frost line can often go below four feet. The area betwwen joists at the rim joist should also be caulked, insulated & have a vapour barrier.

 
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