How can I get rid of moisture between the vapour barrier and the insulation in a basement?

David Mitchell Aug. 14, 2018, 6:32 p.m.

It's a fairly new house (about a year old).  The concrete basement foundation walls are framed (wood), insulated, sealed with a plastic vapour barrier, but not drywalled.  

I am led to believe that, during construction, the builder didn't immediately seal around the basement windows before he installed the insulation in the basement.  Subsequently it probably rained and moisture got in through the unsealed basement windows.  Now, I can see the condensation on the inside of the vapour barrier i.e. the side closest to the insulation.  The vapour barrier is dry to the touch from inside the basement.

Responses (1)

Ecohome Aug. 18, 2018, 1:45 p.m.

Hi David, 

The answer is actually pretty easy but not one you probably want to hear, you should remove the poly. 
Any moisture that may have leaked in through unsealed windows would be a drop in the bucket compared to the amount of water in the concrete foundation, which takes years to fully dry. And even that can only happen if it is protected with a membrane to prevent it from absorbing more moisture from the ground. 
Either there is no exterior moisture protection separating concrete from the ground and it will just stay wet forever, or it is protected from absorbing moisture on the outside, but still the only way the moisture in the concrete can dry is to the interior, which is currently being stopped by your poly vapour barrier. 

So the short story is, despite that fact that so many builders keep putting vapour barriers on the interiors of basement walls, it is the worst thing you can do down there since the main source of moisture is not interior humidity in the air, it's the wet ground and (or) the concrete itself. 
Here is an article that will better help you understand why the walls are wet and how renovations should be carried out - 

https://www.ecohome.net/guides/2270/basement-renovations-how-to-prevent-mold-when-retrofitting-basements/  

Having to remove all the poly is probably not the news you were hoping for but you are at least fortunate in the sense that there is no drywall on at this point. Most people only find out their basements are rotting many years after they've been finished. 

We can help you with whatever steps you take moving forward, so feel free to send along some pics if you can, or at least let us know the following - 
Are the wood studs right against the foundation or is there any rigid insulation panels or membrane separating it from the concrete?
Is there any damp proofing spray on the exterior wall, and or a dimple membrane? 

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