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Fenty 12-20-2008 01:04 PM

Basement wall frost
I live in Northern Ontario and have begun to insulate the perimeter walls of my basement. The walls are concrete block. Initially I installed tar paper against the concrete and then built walls form 2X4's and installed them 2 inches from the concrete walls. I then insulated with R24 batt insulation. I noticed today that where I have insulated that there is frost between the tar paper and insulation on the wall above ground level.
Is this because I have not yet installed a poly vapor barrier?

Any other suggestions?

I am some what frustrated at the moment!!!!!!!!!!!!!!!

glennjanie 12-20-2008 06:26 PM

Welcome Fenty:
There is no need for the poly layer with the tar paper already there. Its just that the block wall is outside the insulation and vapor barrier and still gets the moisture and cold temps from the outside.
Masonry always has some moisture to it but you have a barriere point to keep it in the masonry where it should be no problem. It would still be wise to assure water flow away from the house, use gutters and maybe even paint the foundation outside to keep out some moisture.

inspectorD 12-21-2008 06:59 AM

The reason you have frost is due to the vapor barrier(Tar paper) being on the wrong side of the heated space.It is trapping the water and freezing it.
The tar paper is also vapor permeable, which means it cannot hold back the water from the block. If you had used plastic instead of the tar paper and sealed it at all the joints, this may have worked to delay water migration and let the water disperse into the room. If you where to install the plastic, you may have trapped the water behind the plastic and caused serious water issues to the wall system.
To sum it up,
Vapor barriers always should face the heated side of the space,and be permeable. Tar paper or kraft faced is best.

Plastic or waterproof membranes can be placed on the interior, only after the exterior is up to par. Remember there is really no waterproof, only water control and diversions.

Try Building Science Corporation for more info for your issues.
Hope this helped.:)

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