Replies

1. GBA Editor
   Martin Holladay | Oct 15, 2015 05:59am | #1

   Emma,
   No, you can't effectively insulate a concrete-block wall by installing insulation in the cores of the block.

   First of all, in a well-built concrete-block (CMU) wall, not all of the cores are empty. Some of the cores should be filled with grout (soupy concrete) and rebar.

   However, the main problem with this approach is that concrete is a good thermal conductor, so you get massive thermal bridging. The heat just follows the obvious path -- through the concrete -- and the flow of heat is barely affected by the small pockets of insulation.

   To insulate this type of wall, you need to install a continuous layer of insulation -- usually rigid foam insulation, although mineral wool panels are another option. The insulation can be installed on the interior or the exterior of the wall -- although installing the insulation on the exterior is almost always preferred, because that approach can address the intersection of the wall and the concrete slab better than the interior approach.

2. 
   Chaubenee | Oct 16, 2015 02:37pm | #2

   Two inches of taped foam on outside with furring strips to hold the siding every 16oc. is how I would do it.

3. Expert Member
   Dana Dorsett | Oct 16, 2015 04:09pm | #3

   Sprayed foam never works in CMU cores anyway- they ususally use non-expanding injection foam. While it's R-value is pretty good (R5 per inch), the thermal bridging of the concrete webbing robs it of most of it's performance. A continuous sheet of R6 on the exterior would outperform an injection foam solution in 8" blocks.