GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Using rigid foam on a concrete block house – Northern Ohio

Tim2015 | Posted in Plans Review on

I currently have a 1947 one story – exterior concrete block house(2000sf) with 2X2 interior framing filled with batt insulation. That is covered by a mix of wood paneling/drywall. The front of the house already had a 4 inch styrofoam with a textured stucco put on before we got the house. The block exterior is going to need to be painted this year if I don’t do something. I do not think it was every sealed/primed/painted correctly as paint is popping off. If I do paint it correctly would I now create a moisture issue? There doesn’t seem to be any vapor barrier when I look in via the electrical outlets as I see concrete block and I am unsure if the blocks are filled with anything. Since we heat with wood and then radiant heat if it gets too cold we normally have low humidity and have to run a stand alone humidifier continually to keep 30-35% moisture in the winter. I feel I am pretty much heating the outdoors. I am unable to touch anything indoors per my other half.

I have had a couple of foam companies visit about pumping foam into the blocks to help with heat retention. I worry about thermal bridging with the foam negating some of the foam’s benefit. Additionally, we have a solid 8-10 inch concrete floor/slab and we are built into a hill so the back of our house (half basement and crawl) is fully exposed to the outdoors. The basement portion is a solid concrete wall so I would assume just filling the upper block with foam would still allow the lower wall to wick cold like it always has to the floor in our living spaces up top. The foam would be an easy solution as the would take a day to do it, but again I am trying to determine the cost benefit.

My question is could I use Thermapink XPS 18 R-20 (seems to be used for roofing, but I have it readily available at a low cost) and Tapcon it to my block/concrete block and then stucco over it after appropriate sealing etc? I believe this would seal my house better than any other choice I have read about and be in the budget I have set. I would have to make sure the windows are redone to deal with the 4 inch foam but with my low humidity and 4 inch foam I was hoping moisture wouldn’t be an issue internally. Any thoughts on my plan and if the XPS foam would be usable in a vertical application?



GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    It's too bad that someone in your family doesn't want to allow you to add any insulation on the interior of your house.

    The best way to insulate your basement slab is to add a layer of EPS or XPS on top of the slab, followed by plywood and new flooring.

    The best way to insulate your basement walls is to add a layer of rigid foam to the interior side of the concrete walls.

    Your plan to add XPS and then stucco to the exterior side of your above-grade CMU walls is a good one, as long as you understand moisture management and flashing. Keeping rain away from your windows and doors requires a thorough understanding of these issues; if you are experienced at this work, you're all set. If you are somewhat hazy on moisture management issues, I would hire an experienced EIFS contractor or stucco contractor to do the work.

    In the meantime, you should disconnect your humidifier. That's what's making the exterior paint pop off your walls.

  2. Tim2015 | | #2

    Thanks for the response! I guess I should clarify that our 1st story floor is the concrete slab I was mentioning which is covered with hardwood flooring and only gets noticeably cold near the outside walls. Of the basement, 1/3 is actually livable and the remaining I am assuming is filled with gravel which the rest of the house sits on as there is no entrance to it. I probably should not have used the word crawl as there really isn't any. So there is no option to insulate 2/3 of the basement from the inside. No, I would be the hazy type so I will take your recommendations. Thanks again, Tim

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |