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Moisture question with rigid Insulation on interior of poured concrete basement walls.

George Heinrich | Posted in Green Building Techniques on

Hello,

I know this question may have been beaten to death, but I haven’t been able to find this specific details in any of the posts on here yet.

I have a basement with poured concrete walls that have a slight moisture issue (they weep very slightly in spring and fall when it rains excessively). So I know that I’m supposed to insulate them using EPS, PolyISO or closed-cell spray polyurethane foam and then build my walls on top of the insulation. I also understand that I should NOT use any vapor barrier so that the moisture doesn’t get locked in.

But my question is, what happens to the water that weeps/wicks through the walls and settles between the wall and the rigid insulation? Won’t mold eventually form at that juncture? Or are these types of insulation permeable enough to allow for eventual drying (it doesn’t seem like they are to me).

When we moved into the house, the owners who originally bought the house back in 1954 had put up tar paper, then furring strips, then T1-11 sheeting to create finished walls. When I pulled them down the backside of the tar paper had some mold on it so I know water had been getting through the foundation walls.

Thanks,

George
Philadelphia Suburbs

Replies

  1. Aj Builder, Upstate NY Zone 6a | | #1

    The best advice is to fix the water problem. Ask some basement pros to take a look and give you prices. You might do better than getting internet help as our eyes are not onsite.

    One DIY plan, Drylock two coats on the walls and floors. Hydraulic cement in cracks. Then install all. Heat, air circulation, and dehumidifying all helps.

    But basically finishing basements is risky business. Better to add an addition for dry moisture free space.

  2. George Heinrich | | #2

    Thanks for response AJ Builder!

    George

  3. GBA Editor
    Martin Holladay | | #3

    George,
    As you probably know, visible moisture on the interior of a basement wall can be either condensation or water intrusion. If you know that the water you see is associated with rainfall, than you seem to have figured out where the water is coming from.

    You really shouldn't insulate your basement wall until you solve your water-entry problem. Start with the basics: adjust the grade around the perimeter of your foundation so that it slopes away from the house, and be sure that your roof has good gutters and good conductor pipes that convey the roof water away from the foundation.

  4. George Heinrich | | #4

    Heya Martin,

    Thanks for the reply. I've already checked out the gutters and my house is situated strangely...is situated so that the front of the basement is fully burried but the back wall is only about 2 feet below grade. Therefore, the sidewalls range from fully below grade at the front to only 2 feet below grade at the back. The strange thing is that some previous owner had a 2 foot wide, stepped concrete pad-like thing poured around the house right at the ground level. I'm not sure if they did it to try to fix the water issue or not. I've thought about trenching around the house to fix the outside water issue, but the concrete would have to be jack-hammered out of the way first...very strange. I've never seen anything like it before.
    Thanks for the suggestions though...I may have to just keep the walls uninsulated because I have a feeling it will be prohibitively expensive to have the concrete removed and the water issue fixed.
    George

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