My basement has some glass block windows, that seem to be improperly (or not-optimally) installed. See picture....

Glass Block Windows

As I understand it, there should has been a perimeter channel attached to framing, and the glass blocks installed into that. As it is, I get a little cold air radiating (possibly leaking from outside) out the top.

I was thinking of using spray foam to cover the top, but I'm not sure how that will affect the gaps between the blocks. I'd like to seal it as best I can, and then possibly use XPS + foam on top.

I wonder if I can cut up a perimeter channel and use some caulk to glue/seal it to the top? I'd have to do it in several pieces (one strip between each set of joists).

Edit - In case it matters, here is the larger view; I might do something a little different where that cold air return duct is.

enter image description here

2 Answers 2


Buy some anchors and attach them a good few inches up on each side, and across the blocks. Throw some mortar or a generous amount of glass block adhesive on top of the anchor (you can also screw it into the joists). Throw a 2x4 firmly on top of mortar so your gap is equivalent to your other gaps. Then secure the 2x4 (might even think about 2x6 for this installation) to the joists with a few screws on each side. Caulk any corners or gaps.

This will finish your install and keep the air leak issues. As it stands your blocks are kind of dangerous right now. That middle one isn't secured and when these things fall and break... they explode and shards could be in person they explode on. The anchor and top plate will fix this issue and help fix your air issue too. (If you still notice any drafting after caulking I suggest smashing some roxul into the area.

  • Thanks; seems like a great method. I hadn't seen those glass block anchors; just the perimeter channel. One thing to note is there is no or very little space between the top of those blocks and the joists, so I'll have to be attaching the 2x4s between everything. Jan 11, 2016 at 15:26
  • It is a pretty easy job. You will probably spend most of the time trying to secure your 2x4s in the tight areas (you can use wood glue if you think you can't screw them in). From demoing many a glass block, even a little stability for that top row will give peace of mind. However this install was just done plain wrong as it should probably have a top plate under the joists.
    – DMoore
    Jan 11, 2016 at 15:36

It's hard to see how big that is but I'd cut some 2x4 and fill the gaps as best I could. Then fill any remaining gaps with expanding foam.

Then once that's dry, cut any ugly expanding foam with a blade to make it tidy and cover/tidy the top with architrave or similar.

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