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I recently pulled off old wood paneling in my basement, and would like to insulate it using rigid foam (silverboard or durofoam). Behind the panelling, there is tar paper, and 1x2" studs approximately every 1.5 feet. I see the tar paper as extra protection/moisture barrier, and am inclined to install the rigid foam over top. I have gotten such a range of advice on this...

Option 1) keep tar and studs, fasten rigid board on top leaving a 1-inch air gap between the wall and foam - and build a frame in front of foam for drywall.

Option 2) remove tar paper and all studs, adhere foam directly to cement wall and build out from there.

Option 3) remove studs, adhere foam to tar paper directly.

Option 4) cut foam to fit between existing studs and use tuck tape and expandable foam to fill in spots.

Does anyone have experience with this type of situation? The home is 65 years old, and we live in zone 6 for weather. Spray foam is not an option for us. Thank you!

Dish
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3 Answers3

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Building Science Corporation recommends the following model these days for basement insulation:

  • rigid foam (or spray foam) directly against wall
  • stud wall (I prefer steel...easier to put up, no mold substrate, really lightweight)
  • finished wall (I prefer paperless sheetrock again, to avoid having a place for mold to grow)

Note the absence of any vapor barrier...of which tarpaper could be considered one.

The foam board acts as a vapor retarder so it slows moisture movement, but doesn't completely prevent it in case one side has to dry to the other.

For more details, see my answer on this question: Should I use steel or wood studs for basement exterior walls?

Community
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DA01
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Option 2 is the best or only sound advice. Here's a class on what's been determined. You can skip the "adhering" of the foam boards & have the stud walls hold it in place without issue.

If building the stud walls in place you'd just temporarily tack the wall's top plate in to hold the foam boards for you while you tape &/or spray foam seams & gaps. If prefabricating the stud walls to be tipped up into place, then the foam boards can be sparingly screwed to the back of the stud wall & then seams can be spray foamed & taped from the back.

Iggy
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Given that this is just nailing strips for the prior wood paneling, there's no reason to try insulating around them. Pull them off and make a continuous insulation barrier for the best efficiency, or frame up new walls and insulate between them if space is a large concern. The tar paper is keeping moisture off of the wood nailing strips, so there's no need for it with the foam insulation. As DA01 points out in the comments, the foam board is only a vapor retarder, and I wouldn't suggest the only vapor barrier being on the outside wall since this can result in condensation problems. So of all the options presented, it looks like option 2 is the best.

Assuming you are going to frame a new wood wall in front of the insulation, do take care to separate the wood base plate from the concrete floor. This can be done by extending a moisture barrier from up the wall 6" or so, out to the floor and under where your new wall will be located. There are also foam gasket products that you can buy in roles to install under the base plate.

BMitch
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