GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Insulating Concrete-Block Foundation

cotto11 | Posted in General Questions on

Starting basement remodel and noticed the tops of my brick wall are hollow.

before I stick 2”  rigid foam up against the rim joists I’m wondering if there’s anything I should do to the hollow bricks?  Obviously the 2” foam would only cover maybe 1/4-1/2 of the block opening.

the first level of my house is brick all the way around, if that makes a difference.

any suggestions?

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. user-2310254 | | #1


    Your foundation appears to be made with concrete block (not brick). As a first step, I would inspect it to make sure you don't have any issues with bulk water entering the basement.

  2. cotto11 | | #2

    Had minor water issues at the joint and had a French drain installed. Seems to alleviated that problem.

    Would rigid foam in the rim joist and laid horizontal over the top of the block work. Sealing all joints with spray foam.

  3. Expert Member
    Akos | | #3

    If the block are hollow all the way down, see of you can source some perlite block fill. This would bump up the R value of the blocks a fair bit. Depending in the type of block, this could be enough insulation, or at least significantly reduce the amount of interior rigid you need.

    You can cap the top with some rigid and spray foam it in place.

  4. Expert Member
    BILL WICHERS | | #4

    If you want to add a capillary break, you can use thin HDPE sheet (this is different from polyethylene sheet like you'd use for a vapor barrier or drop cloth) to cover the top of the block. This will give you an air barrier here too which can help if you have air bypassing the rim joist through the holes in the block (I've had this problem myself). I used 1/32" HDPE sheet with a lip formed on the interior side to make a stop that hangs over the top of the block.

    If you don't want to add a capillary break, I like Akos' suggestion of perlite block fill. If you have something on the exterior of that rim joist that will limit drying (foil faced polyiso, for example), you should consider using something more vapor open on the interior side such as EPS to allow for a small amount of drying for the wood structure there.


    1. cotto11 | | #5

      So my joist is not exposed to the exterior it is covered by brick. My basement block has what I believe is a stucco like material over top. Attached a photo to show what I’m talking about. Not sure if this changes anything.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |