do you need a vapor barrier


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Old 01-13-06, 11:05 AM
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do you need a vapor barrier

I am reading many posts here about when you need a vapor barrier. I just had french drains installed in my basement. I had to cut 4 ft of the wall up and now I am in the process of reframing the bottom portion to the top portion. The walls are away from the contrete walls by at least 5 or 6 inches. I sealed the bottom portion of the walls with dryloks, but I see that the people did not have any vapor barrier against the concrete. The had the wall offset with insulation between the metal studs, the insulation however has a paper backing that says vapor retarder and that part is facing the sheet rock. Do I really need to put a vapor barrier up against the concrete if I have insulation that says "vapor retarder" and the wall is built away from the concrete and not right up against it, plus isn't a "vapor retarder" insulation the same thing as a vapor barrier?
 
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Old 01-16-06, 07:53 AM
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A vapor retarder is like a mild form of a vapor barrier. Scientifically, how easily a material allows moisture flow via diffusion is measured in perm rating, and vapor barriers have lower perm ratings than vapor retarders.

As to why people put up vapor barriers: Neither a vapor barrier nor vapor retarder is designed to prevent airborne humidity from traveling through the wall and contacting the concrete, where it can cause condensation. Generally because for this to happen, you need something to prevent air flow. With vapor barriers, it is easier to provide the necessary taping and sealing to reduce the amount of air flow as compared to trying to tape & seal faced batt insulation.

Realistically, for basements you're better off using a high-perm air barrier like tyvek, or going to a high-perm foam insulation-style air barrier.
 

Last edited by doug thomas; 01-16-06 at 10:46 AM.
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Old 01-16-06, 08:06 AM
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If your Code for your area requires a Vapour Barrier, then you need to install one. 6 mil poly is the best Vapour Barrier. Tape all joints and seal electrical outlets and other penetrations.
 
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Old 01-16-06, 10:49 AM
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Originally Posted by em69
If your Code for your area requires a Vapour Barrier, then you need to install one. 6 mil poly is the best Vapour Barrier. Tape all joints and seal electrical outlets and other penetrations.
Yes 6 mil poly is the best vapor barrier.

But Vapor Barriers are not appropriate for all basements, especially in air conditioned buildings. That's why typical installations are only top 4 feet, not full height.

Did you know that the Canadian & Ontario codes pretty much say "our vapor barrier codes don't really apply to air conditioned buildings"?
 

Last edited by doug thomas; 01-17-06 at 07:34 AM.
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Old 01-17-06, 06:45 AM
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Most Canadian cities are in heating mode more often than A/C. This is why the VB is applied on the interior side of the insulation. 6 mil poly is the minimum Code requirement.

Typical insulation installations are only 4 feet because that is what's required to meet the "minimum Code requirements".

If you want your basement to be a comfortable living environment in a cold weather climate, then you need full height insulation. If you have full height insulation, then you need full height VB.

As for the barrier which the original poster is questioning...this is called a moisture barrier. This is also required by Code in certain parts. This is to prevent the insulation from contacting the concrete wall.
 
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Old 01-17-06, 07:43 AM
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I'm pretty sure most people stick to top 4 feet because they don't want the liability associated with putting a full height VB in a basement. I know in my unfinished basement we have the water stains on the concrete to justify the use of a top 4 foot installation.

I tend to agree with these guys:
Basement Insulation Systems @ Building Science.com

You have to love quotes like this one:
"The experience by the Building Science Consortium with [full height batt + VB systems] has been bad. The Building Science Consortium
has concluded that these two approaches are unsuitable for use
by the home building industry due to serious problems
associated with mold, decay and odors. This is consistent with
reports from Canada where basements are insulated in a similar
manner (Fugler, 2002) and from other researchers in the
United States, notably in Minnesota (Ellringer, 2002). Continued
use of these approaches by the home building industry will
likely lead to a disaster of unprecedented proportions and may
result in the construction of energy efficient homes being set
back a generation."



And Brian Hunter isn't asking about a moisture barrier. He's asking if the Vapor Retarder facing on his fiberglass will need additional poly.
 
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Old 01-18-06, 06:24 AM
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In cold weather climates, 4 feet of insulation is insufficient in making a basement area liveable. You would need an additional heating source.

CMHC was one of the references for this research. Before I finished my basement, I contacted them and requested specifications for basement wall insulating, vapour and moisture barrier installation. I built my walls to the exact specifications they provided me, which is what I provide to others for info in this forum. These specifications exceed the "minimum Code requirements" and is also recommended by several organizations and professionals.

This article seems to only discuss examples where the basement walls are wet. As long as you deal with any moisture issues effectively, then typical insulating methods are fine. I have a Platon Foundation wrap around the exterior of my foundation. Soil is never in direct contact with the concrete wall. This is one of the best ways to avoid wet walls.


The water stains on your wall will disappear only if you repair the problem on the exterior.
 
 

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