Which insulation?

bert76April 9, 2010

We have a finished basement that was done by previous owners. We know there is no insulation.

We have discovered mold that likely started when the previous owners had several floods before putting in a sump. The basement has been dry in the two years we've owned it.

As part of the remediation, the drywall will be removed 4' up from the bottom (the mold is only on the bottom couple of inches).

We're going to leave the walls open for a while to see if there are any unknown leaks. Once we are comfortable that we've solved any moisture problems, we plan to reinstall paperless drywall. But we also want to add insulation. It has to be non-organic and non-porous to inhibit any future mold growth.

For this type of situation, what kind of insulation would be best, keeping in mind that cost is a factor. Could we put insulation boards (XPS, I think) in each stud cavity? Would that provide the right kind of vapor barrier?

Thanks for any and all advice.


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Any of the following materials will work well in at least the thickness specified.

XPS up to 2ins.; EPS 4 ins.; closed cell spray polystyrene of 3 Ins.; open cell spray polystyrene, 10 ins.

No vapour barrier needed. (Unless a clueless municipal inspector still insists on it.)

If you can slip sheets of XPS between the framing and the foundation walls, do so. Even if it's just 1/2" sheets, it will be very effective in reducing moisture.

Here is a link that might be useful: Building Science Corp. on Basements

    Bookmark   April 9, 2010 at 1:18PM
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Thanks. Should I try to seal around the XPS? Or just put it in the cavity against the concrete?

    Bookmark   April 9, 2010 at 2:41PM
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Any thoughts on the most economical rigid insulation? What about the best way to install, considering the drywall is gone four feet from the bottom?


    Bookmark   May 18, 2010 at 3:51PM
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As long as the boards are tight to the wall, there's no need to seal.

EPS is the cheapest satisfactory insulation. But it robs space because of its thickness. The most important part of the basement to insulate is the top of the wall, especially the portion that is abovegrade. If you're trying to keep the drywall, I'd try to push up enough EPS so that it tightly fills the space. Not ideal. But it could be effective.

    Bookmark   May 20, 2010 at 9:35AM
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Does it matter if the exterior basement wall has a covered porch or garage (on a slab with dirt fill) on the other side?

I have an insulation company as part of a weatherization program here today, and they said that this situation is like a 'party wall' and doesn't need insulation since it's not an exterior wall.

Does that make sense?

    Bookmark   May 25, 2010 at 4:53PM
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By the way, none of these wall in question are above grade.

    Bookmark   May 25, 2010 at 5:15PM
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