Here is the issue, my basement wall facing south is trapping moisture. Removed the drywall and found a layer of poly and rigid insulation on the lower wall and batting insulation on the top side. The 2x4 framing studs are built above the footing blocks but on the inside they put 1x6 furring strips and drywall over that The exterior brick wall under the window shows efflorescence. Btw, my footing is above grade. Would this have been caused by water/moisture from the exterior brick wall/ window or internally from the vapor barrier? I've read too much information about basement wall insulation and some say to insulate it some say don't.

any help or information greatly appreciated.

  • Your footing is above grade? How does that work?
    – Ecnerwal
    May 28, 2015 at 14:19
  • We need pictures. As Ecnerwal points out, a footing, by definition, can't be 'above grade'.
    – DA01
    Jul 19, 2015 at 18:32
  • That said, I'm a fan of never using vapor barriers (as in plastic sheets) in basement walls. Use only foam board insulation which acts as a vapor retarder.
    – DA01
    Jul 19, 2015 at 18:33

2 Answers 2


The correct way to insulate a basement wall is with rigid foam or spray foam right up against the masonry walls, with air sealing scrupulously done with caulk, tape, and more spray foam, to make sure that no humid air can touch the masonry walls. Once that's done, you can safely build a framed wall covered in drywall if you like to finish the space. There should NEVER be poly in this wall sandwich, as it will trap water and cause everything touching it to get wet.

If you currently have a wall that has poly anywhere in it, you need to remove it. Then redo it according to the above description.

  • This is an excellent way to insulate an existing basement. But it is not the only "correct" way (another way to insulate a basement is to dig around the foundation and add insulation the exterior). Also, just to make sure, did you mean "to make sure that no humid air can touch the drywall." where you wrote "to make sure that no humid air can touch the masonry walls."? In an interior insulation-only install, the foundation/masonry walls will most likely be wet at some point due to contact with soil and that's okay. May 20, 2015 at 17:09
  • It is the only correct way to insulate a basement wall from the inside, true. I meant what I wrote. It's true that the masonry walls will be moist due to soil contact, but that's no issue; the problem is not vapor diffusion but rather air movement. The point is to prevent humid interior air from touching the masonry walls, where they it condense into liquid water.
    – iLikeDirt
    May 20, 2015 at 17:42

You have not discussed what the trapping of moisture symptom is? It sounds like you found your poly under the sheetrock? It should be against the masonry. Just an opinion. Jeff

  • 1
    No poly anywhere in a basement wall ever!
    – iLikeDirt
    May 20, 2015 at 16:15

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