Fixing Condensation Behind Basement Insulation

Question Icon
Posted by: from Winnipeg
3/9/2013 at 8:09:01 PM

Hi all,

This is our second winter in a newly built house. The basement was insulated with a layer of poly against the concrete and framing done about 2-3 inches off the wall. One layer of fiberglass batting is running horizontally and set in between the concrete/poly and the framing. A a second layer of batting is then running vertically between the framing for a total of two layers. There is then another layer of poly on the inside sealing it off. So it is concrete - poly - horizontal batting - framing - vertical batting - poly.

The problem is moisture has found a way in and there is considerable condensation between the poly and the horizontal batting. There is frost formation and it has condensed enough to seep out the bottom (which is how we noticed the problem).

I've opened up a few areas to assess, but am wondering what the best way to resolve this is? The ground will still be cold for another month or two (we're in Winnipeg) so I'm not sure if it's best to wait for things to warm up and the frost melts, or if this is urgent enough where I should start trying to rip out insulation now? A lot of insulation is actually frozen to that layer of poly on the concrete so it'll be messy.

Thanks for any advice.

User Icon
Date/Time3/9/2013 at 9:11:25 PM

The biggest problem is the two layers of poly you should have poly on the warm side only not up against the concrete also. Standing in the room looking at the wall you should have drywall poly insulation and framing and in our quotes we always include waterproofing the concrete or cinder block.

Hope this helps.

Chris Tooley

User Icon
Date/Time3/9/2013 at 10:39:35 PM

In southern Alberta we never put poly against the foundation wall, we only poly the worm side of the insulation.

User Icon
Dave from 360renos in Navan
Date/Time3/10/2013 at 11:17:48 AM

I would leave it for now. let it warm up, then tear out all the insulation out and start fresh

Not sure of the National Building Codes for your area so you should find out before replacing materials to ensure it is completed correctly. I'm in Ontario so we use the OBC

You want an air barrier membrane against the foundation wall not a vapour barrier.

The poly vapour barrier only goes on the warm side of the insulation. What you currently have lets any warm air that enters the insulated area to condense and form water droplets and then freeze to the foundation wall. The warm air has nowhere to escape and gets trapped between the two layers of vapour barrier.

One area that is quite often missed and most likely is a cause for issue is to ensure when the new vapour gets installed that EVERY SINGLE entry point for warm air is either taped, and/or acoustic sealed. This includes the header area especially. No warm air behind the vapour barrier means no moisture/water damage.

A little reading that may help with understanding some correct ways to insulate


User Icon
Date/Time3/10/2013 at 11:56:52 AM


Strip both poly and batt insulation now. (It never fully dry). Than install another layer of any insulation (R24 if enough space). Apply Super Six poly on warm side and seal it around with sound insulation caulking (including around electrical boxes etc.) It must work.

Good luck.


JMB Canpol Builders Ltd.

User Icon
Date/Time3/10/2013 at 12:20:07 PM

If you are installing pink or batt insulation wether it be nailed to the concrete wall or within the framing. The layer or poy should then be installed. This should be taped with tuck tape. Ever join, evry seam. No penetration of warm air into the insulated or cold side of the structure. And only one sigle layer of poly should ever be used.

Now, there is a better material to use, but this is for you folks that don't have framing up yet. And don't mind spending a little more money.

In my own new home, I tore down all the pink and poly the builder threw up. Then using PL300 I installed 2x8' Dow Styrofoam. This is the 2" R-10. Then I framed the outside wall of my rooms in the basement. Ran all of my electrical and plumbing. I found the basement warmer after doing this than the builders R-12 pink. If you desire, you can add some more batt insulation in the studs of the wall at this point.

I also strongly suggest a sub floor such as DRI core. These 2' x2' panels fit together and the thick layer of channeled plastic on the down side allows the concret to breath and any water that gets into your basement in the future to run towards a drain. Over that you can run broadloom or as I have done, 1700sq of laminate.

Remember. One layer of poly on the outside wall. And keep the cols air on one side and any warm air on the interior side.

Good luck.

User Icon
G in Winnipeg
Date/Time3/10/2013 at 12:46:26 PM

Thanks for the replies everyone.

I will definitely be tearing it all out and doing this right..... it's just a matter of when. It's a balance against time for mould growth, but I'm leaning towards leaving it in for another month or so for things to warm up so when I do open it all up it can really dry out.

Right now the fiberglass batting is frozen to a layer of frost on that poly against the foundation wall. It won't come out easy and I'm afraid I won't get that cold wall to properly dry. Till then I think I'll just leave it sealed up. I am going to check more into getting it done with rigid foam insulation.

User Icon
Date/Time3/10/2013 at 9:45:19 PM

If I understand correctly you have concrete then insulation...then vapor barrier...then insulation! I am going to tell you from everything that I have done the vapor barrier must be on the warm side, so concrete framing with vertical batts then vapor barrier with acoustic sealant applied at all edges left, right, top and bottom.

There should be in a 2 yr old home also a breathable fabric such as tyvek (house wrap) on the inside of the exterior wall, maybe only applies in Ontario.

Your moisture is coming from condensation being trapped between the vapor barrier and the insulation and just drips down and can puddle.

I would rip out all the insulation and vapor barrier and have spray foam installed, more expensive but a much better way of doing things!

Hope this helps!

Good Luck!

User Icon
Date/Time3/10/2013 at 11:47:45 PM

What you have, we call a moister sandwich two layers of poly with a heaping pile of insulation and moister in the middle. The correct way to do this type of basement is tar membrane or a capillary brake on the outside, 8" of concrete, one inch of air space, wood framing filled with insulation, poly vapor barrier then add your drywall and so on. You can add better types material for each layer depending on how much you would like to spend.

The wall system should be done right from day one. Since the home is only two years old, I would approach the builder and see what his intent was when he did it this way and if he admits that it is incorrect. I would tell him that this is a latent building problem and it should be up to him to fix it. If he resist go to your new home warranty provider for a consultation. They may have some good answers for you.

Good luck

Mr. H Gavacs

Man Zone Construction Ltd.

Search the TrustedPros directory and discover the best contractors in your area.

Find your home service pro
Great renovations start with a great contractor.

Since 2004, TrustedPros has been helping homeowners find the right contractor for their home improvements and repairs.

Post Your Project

Within hours you'll be comparing offers from top-rated professionals. It's free to post and you're under no obligation to hire.

Trustedpros Inc. does not warrant the accuracy, completeness, safety, legality or usefulness of any Content, or Whether Content is Current and up-to-date, and TrustedPros Inc. Shall have no liability whatsoever with respect to your use or reliance upon any content or for content being removed or otherwise ceasing to be available. Please refer to the terms and conditions of use of this websites for more details.

Get Free Estimates

Post your project and compare offers from top-rated pros.