We had a moisture problem in our basement located in Minnesota. Recently some foundation water came up and ruined our carpet, when we tore out the drywall there was moisture build up and some mold on the walls. The exterior wall was removed and a Waterguard drain system with sump pump installed with a plastic sheet/water vapor covering the entire wall and tucked into the drain.

My question is how do I insulate the exterior basement wall now that the plastic vapor barrier was installed with the drain system.picture of wall with new vapor barrier](https://i.stack.imgur.com/Juif2.jpg)picture of wall with new vapor barrier

  • how bad is your basement? is it a long-term issue? Do you have some pictures? Can you move some exterior framing?
    – DMoore
    May 18 '20 at 18:48
  • Insulation and vapor barrier don't need to be coupled. You can re-frame the energy walls and insulate as you see fit. Just don't add a second vapor barrier layer. Do you have a more specific question?
    – isherwood
    May 18 '20 at 18:50
  • The mold was minor but it was obvious that the moisture was a long term issue, we bought the house two years ago. To help clarify I did add a picture of the current status with the drain system installed and plastic barrier. I just want to know the best way to insulate it now and not trap moisture in the walls, most people say to use XPS foam board? May 18 '20 at 19:24

You can do almost anything since it should be fairly dry on the inside side of the vapor barrier. Best would be some kind of material that can tolerate a little water and resists the flow of vapor. Any humidity in the basement air will tend to cool when it touches the vapor barrier and condense into water on the wrong side of the vapor barrier.

Sheet XPS or PolyISO Foam with seams taped would work and be an easy DIY project.

Better would closed cell spray foam installed by a contractor.

For a lower budget option you could go with a mineral batt insulation that is vapor open but will tolerate being wet without being a food source for mold.

Fiberglass batts are probably the worst choice since they tend to degrade in moist areas. I would not recommend them.

Do not put an additional vapor barrier on the inside side of the wall, this will just trap moisture inside the wall cavity.

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