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Finishing a basement wall that has previously been painted

mkendall1234 | Posted in General Questions on

I am in the process of framing up a basement that has previously been remodeled using panels that were directly glued to the solid poured foundation. As I am removing the wall covering, I am noticing that the concrete has been painted previously. My plan was to remove any adhesive, wash walls with a TSP substitute and allow area to dry. I was planning on using 1/2″ EPS glued to the wall and place more EPS in the rim joists and using a fire retardant foam to seal in those areas. I was then going to leave a sight gap 1/2″ at the bottom of each panel and seal all seams with tyvek tape. I plan on placing traditional 2×4 construction over these and fill with roxul. I was thinking about gluing a second 1/2″ over the EPS and overlap the seams due to shrinkage over time, but maybe this is overkill? Also, I wasn’t sure if there was anything else I needed to do like a special paint over the previously painted concrete? The basement has no water problems. For the sill I was planning on using treated lumber and place a foam gasket underneath. Any advice regarding the prepainted walls and plan would be greatly appreciated. I am in Iowa if that helps.

Thanks again!

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  1. GBA Editor
    Martin Holladay | | #1

    1. Don't worry about the paint.

    2. The minimum thickness of the rigid foam layer depends on your climate zone. The colder the climate zone, the thicker the rigid foam layer needs to be. A conservative approach would be to follow the rules for above-grade walls provided in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing. (Even though the article isn't about basement walls, the same ratios mentioned in the article can be used for basement walls.)

    So, in Marine Zone 4, your rigid foam layer needs a minimum R-value of R-2.5; in Cimate Zone 5, you need R-5; in Zone 6, you need R-7.5; and in Zones 7 and 8, you need R-10.

    3. For more information on the work you will be undertaking, see this article: How to Insulate a Basement Wall.

    -- Martin Holladay

  2. Expert Member
    Dana Dorsett | | #2

    What is the purpose of the half-inch "...sight gap..."?

    If the paint isn't failing it means the moisture drives from groundwater are pretty low, and it's fine to just insulate over it using generous amount of foam-R above the code minimums required for dew point control in your climate zone.

  3. mkendall1234 | | #3

    I thought I needed to keep a slight air gap at the bottom of the panel. I meant slight gap not sight gap. Sorry about that.

    Thanks for the reply and the links. Is there a maximum air permeance I need to be looking for in an Expanded Polystrene? I'd prefer EPS due to less off gassing and shrinkage. If I want to get to the recommended R-5 it looks like I'll need to install 1.5" panels on the outside wall to reach R-6 in one panel. One company claims air permeance of <1.0 and R4 per inch and another claims <3.5 and R5 per inch. Would either of these work? Would there be an advantage to one over the other?


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