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Question about XPS rigid insulation on basement walls

mg550 | Posted in General Questions on

I have a poured concrete foundation that has a simulated brick texture. If I install 2″ XPS insulation against the walls there will obviously be voids because the foam can’t sit flat against the wall due to the texture. I’d say the depth of the recessed area is a 1/4″ maximum.

I guess my question is will this present any problems?

I’ve attached an image for reference.

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Replies

  1. Dana1 | | #1

    The uneven surface is not a problem- in some ways it's beneficial as a capillary break.

    To keep it from becoming a parasitic thermal bypass channel for infiltration & convection you have to make the foam as air tight as possible, but that would still be the case if it was smooth poured concrete foundation.

    XPS is the least green of the commonly used rigid foam products, due to the high global warming potential of the blowing agents used in it's manufacture (HFC134a, with a GWP about 1400x CO2.) EPS & polyiso are both blown with pentane, at a GWP of only 7x CO2. Either can be used in this application, foil-faced polyiso would be easier to air-seal, since there are purpose made aluminum FSK tapes for sealing foil facers. When using polyiso, keep the cut bottom edge off the slab, since it can otherwise wick moisture into the foam. EPS does not have this issue.

    At the same R value both polyiso & EPS are usually cheaper than XPS too.

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