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An old addition room to a unit has structural issues, it was more than a hundred years old, and the floor structure was rotten, turns out they used a large beam in a reverse brick shelf right on the foundation.

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So a large beam just like the image, was resting on a notch right in a stone foundation, joists connected in a similar manner to the image. What was left of it at least, I found a section of beam that wasn't complete dust to notice the notches. It wasn't a raised wood floor, it's a drop floor, joists literally touching dirt in some spots.

the stone foundation wall appears sound around the perimeter, so my thought was to pour a slab. The space where the old joists rested is about 8 - 10 inches, just about the right depth for gravel and a slab, and I'd put new flooring over that. Problem solved, or so I thought, but not quite....

Turns out there was an old stair well a little from the edge of the room, approximately 30 by 60 inches. It was covered by the old joists.

What should I do? Pour the slab, minus the stairwell, drop joists in in the stairwell, then plywood sub floor over the slab and those dropped joists? The stairwell is like a hole in the ground, the walls of which appear to be old brick, but in sound condition. I think it was an old outside entrance to the basement. It was walled off at the bottom steps long ago, so it could no longer serve as an entrance to the basement, just in case anyone thought not covering it was an option. It's also inside a room now, I'm not sure an outside style basement entrance would feel too homesy.

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If that stairwell is just a hole in the ground than you should be able to simply remove any old wood and other organic materials. Then just fill the hole with soil similar to the surrounding soil in layers and pack it well as you build up to grade level.

If that stairwell entered into an opening (doorway or archway) into a below grade space (such as a basement, crawl space or 100 year old root cellar) than you may have to deal with closing off that opening with a poured concrete wall structure before you can then fill the space in your slab area as discussed above.

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  • I think it's closed off at the bottom of the well... maybe not perfectly, but I could repoint if needed. You think it would cost less than dropping joists and playwood subfloor? Apr 21, 2023 at 22:51
  • If the closed off wall section into your basement is in good condition then I would evaluate if you need to apply moisture barrier to the outside of it and then go ahead and fill it up with soil like I suggested. It is hard to be more specific without a bunch of good pictures from all aspects added to your question.
    – Michael Karas
    Apr 21, 2023 at 23:21

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