We are having HVAC ductwork installed in our crawlspace and one of the companies mentioned they do not remove foundation concrete blocks due to liability. Unfortunately, for us to have registers in our living room at least one concrete block needs to be removed from an interior wall. I have looked online and it appears to be a straight forward job in removing the block.

My questions: Do I need to worry about the structure of my home when removing one or more concrete blocks from an interior wall? If so, how many blocks need to be removed before I need to install a lintel or some other support? Does where the block is removed on the wall matter? Thank you and any advice is appreciated!

  • If it's such a straightforward, risk-free job, you have to ask yourself why the company doesn't want to touch it. BTW, are you sure an entire block needs to be removed, rather than drilling a hole through one? Also, is the plan to just remove the block and leave a hole, or replace it with something structural containing the minimum hole needed for the duct?
    – fixer1234
    Jul 21, 2018 at 0:54
  • Are these the standard concrete blocks 8 in x 8 in x 16 in? Jul 21, 2018 at 3:25
  • @fixer1234 'foundation concrete' that is why the company will not touch it - you touch it you own it no matter how simple. Ever hear the saying if it ain't broke don't fix it, or don't kick a lying dog .. The company is protecting itself..policy covers everyone's home not just the op's.
    – Ken
    Jul 21, 2018 at 10:40
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    @Ken that is where they are coming from, a small company who is doesn't want to take on that liability. Even if they do their part perfect and we were to have structural issues down the road, they would have been the last one to have made changes to our structure.
    – wharkins3
    Jul 22, 2018 at 2:00
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    Have you ruled out all other approaches that don't require messing with the foundation? For example, duct work is typically routed between floor joists, which can be done above the foundation, or worst case, notching out the top of the foundation. re: minimum scope warranting consultation--I would say pretty much any change of this nature would warrant consultation with an engineer or foundation specialist. I wouldn't worry about a small hole for a screw or to pass conduit through, but anything big enough for duct work, yes.
    – fixer1234
    Jul 22, 2018 at 2:14

1 Answer 1


Yep, you need to worry about the structure. You may be fine with a pressure treated box-frame inside the void, if the section isn't directly load-bearing.

But typically, a proper steel angle lintel is required and that must run at least over half of the neighbor block width. A call to a Mason might surprise you with how cheap it'll be for them to knock it out.

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