In the basement that I'm finishing I have an irregular, rough stone foundation wall, pretty dry. I'll use 1" XPS foam insulation, then drywall. Can I build the framing on the floor, attach the XPS to it directly, and then just raise the whole assembly snug against the foundation wall? Seems easier than attaching the XPS to the stone foundation.

Thanks for any insights here.


  • Don't forget to fireblock and draftstop according to any local code requirements. Generally, you will need to add a break in the XPS every 10 feet or so (check local codes) and create a relatively air tight seal with the wall using a fire resistant material like pressure treated 2-by lumber. Also, most code references and recommended building practice I have seen call for an R value of at least 10 for basement walls which is generally a minimum of 2" of XPS--again I recommend double-checking local code. Commented Aug 27, 2016 at 10:12
  • Thanks. For 10ft vertical fireblock, can I use a narrow 5/8" drywall piece, say at a vertical seam between sheets of the XPS? If so, is there any kind of caulking or spray foam that I can use to fill the little openings where the drywall fireblock meets the irregular surface of the stone wall?
    – Jeff
    Commented Aug 28, 2016 at 13:30
  • Did you ever get this resolved? If so, please give a check-mark to the answer that helped you the most, or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer.
    – FreeMan
    Commented Aug 3, 2020 at 18:17

2 Answers 2


That's how it's done, don't forget to apply chemical tape to the seams and seal the areas around the wall prior to installing it. You won't have another chance with out removing the wall first.

  • Thanks. So, do you know what kind of adhesive I use to attach the XPS to the back of the studs on the framing?
    – Jeff
    Commented Jun 29, 2016 at 13:05
  • Usually not adhesive. Washered (or "capped") nails.
    – isherwood
    Commented Oct 27, 2016 at 19:27

I’ve had great success using PMF anchors to attach EPS or XPS to masonry and concrete. These work very well to allow for variance in the wall while ensuring a snug fit. Always apply a good seaming tape at the joints. Also, for protrusions or odd angles you need to work on, suggest you have some minimal expanding spray foam and foamboard glue on hand.


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