I just moved in a couple months back and noticed that this wall was a lot thicker than expected, lots of unaccounted for space. I was honestly expecting to find a body in there :P glad I didn't!

The space is only accessible from above, between the joists in the ceiling. I stuck my arm over the wall with phone camera in hand.

The wall is obviously supporting the joists, but I don't know why there are two cinder block walls with about 1 or 1.5 ft between them.

Has anyone seen this before or have any idea why it was done?

I'm planning to increase insulation and do air-sealing, but have no idea how to deal with this space!? One of its sides is an un-insulated exterior wall :(

Video (spider-web warning!): https://www.dropbox.com/s/vvb3f9qdh0eat2e/VID_20190824_122226.mp4?dl=0

enter image description here

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    Not knowing if this was an added construction feature of the residence, or if it's original, that's where seeing some construction plans would be great to see. If you're not able to contact the previous owner, you could go down to the local city or county building department, give them your address and request the ( not always available ) original and modified building plans for the place.... A lot of times, plans will have notes stating the reason something out of the ordinary is done by the engineer who designed it. Good luck / happy sleuthing 👍 – Retired Electrician Aug 31 at 5:03
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    Is there any plumbing in the cavity? I have seen where people built walls to hide plumbing not realizing it could be done with 1 wall. The only other possibility I can think of since it is cinder block is a support structure for a fireplace. – Ed Beal Aug 31 at 15:04
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    What's directly above it on the first floor? – Mark Aug 31 at 15:28
  • No plumbing - there is nothing in the cavity. What we do have is a brick wall on the main floor, so maybe it's just there to support it? I'll take some measurements to see if its directly under the brick wall. I still think its weird to be completely closed off - could have made space for util/mech room. – jpx Sep 4 at 19:55

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