Open Web Concrete Blocks

When inspecting crawl spaces we frequently see open web concrete blocks set so that we can see the open holes. We currently call these out as not providing the necessary support. Some of our inspectors think that if you fill the holes with concrete then that resolves the issue. On the other hand, we could probably assume that the other blocks are probably also open web but they are set the way you would set in a wall and not easily filled with concrete.

Based on your knowledge and experience is it ok to use open web concrete blocks in a crawl space to support a floor structure? If so, does it make any difference how they are laid?

Yes, it is okay but the concrete blocks strength is when they are laid with the cores vertical…NOT horizontal.



Also, make sure they are actually structural and not just filler between piers which is common in old homes.

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Keep in mind that oriented properly the cmu still requires something to distribute the load relatively evenly.


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