First time I've seen this foundation

Inspected a home today built in 1957. Block house - had what I initially thought was a crawl space when I saw the opening… and I thought it weird that it was not covered. When I tried to access it, the space is full with dirt. except a small hole dug out and I can see the trap from what I believe to be the toilet (bathroom is right at this spot.) It’s not a crawl space, not slab on grade… There are no ventilation openings …

Raised slab?

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Most likely they were making a plumbing repair and dug out under the slab.


That’s crazy.

Looks like a slab on stem wall where someone cut a hole and dug a tunnel to somewhere, likely for a repair of some kind.


Agreed, to put in that p-trap I suppose.

Yeah, that looks like a hack job for a repair. They undermined the slab to get to the plumbing. Although, I do sometimes see the underside of slabs and wonder if they were designed to be suspended (usually would have tension rods in the concrete but we have no real way of knowing). I think this one isn’t due to the uneven surface of the concrete - looks like it was initially poured over dirt.

I stayed in engineering school just long enough to pick up a couple good nuggets and suspended concrete was one of them. Maybe one of our helpful engineers has a sketch of loading suspended concrete (beams, etc.)? As the concrete deflects the top is in compression where concrete is very strong, but the bottom is in tension where concrete is very weak. So, if/when you see the underside of concrete it should have pre-tensioned rods in it to keep the bottom from stretching (for lack of a better term). How different materials react when loaded and deflect is a good things to have a general understanding of as an HI. My long-time business partner was a civil engineer and was always the first to point out that inspecting homes and engineering were pretty far apart but this one thing he talked a lot about.


I searched for signs of movement, but found no cracks, etc to indicate any foundation failure. Windows and doors open and close well - especially for this age home! I hate to call for an engineer to look at it, but I think I need to!

No need to wonder here, not in a 1957 residential dwelling like the one in the picture :smiley:

I agree. And have seen it before.

1957, someone had to crawl in there at some point to install that PVC trap. PVC was just barely out in that era.

State no access big enough to inspect the underfloor area, refer them to a foundation contractor for further evaluation AND get it off your back

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I think they just need to get a real plumber in to fix up that trap,
then get a contractor to install a few piers to replace the function of the missing dirt under the slab, and call it a day.

The “span” created by the unsupported slab is the only problem created by the plumbing repair.

Thanks - that was my recommendation. I actually went back out there today to get some better looks - I used a pole cam to look at this plumbing. It;'s in rough shape. The buyer’s Father in law is a licensed plumber, so it may not be too bad for them.

If they shore up the void of the slab, I think they should be able to excavate the area around this plumbing and upgrade the drain.

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I would come in from above and cut the concrete for safety reasons after the void has been evaluated/corrected.

The main choices seem to be:
a) Fill (and try to pack) the void with dirt, then cut the slab from above
b) Shore the slab from below, with screw jacks.
c) Cut the slab from above, and pack it from above, pouring a new slab in that area.
d) Expansive foam (expert installer required).

I’d go with (b) because it will be too hard, maybe impossible, to repack the dirt tight up under the slab. And it’s hard to do (c) and avoid cracks at the new/old boundary.

The cast iron may be rusty on the outside, but what’s important is inside. It might be fine.

Mud jacking / void filling would do it.

Kind of looks like they DID jackhammer the slab to install that repair?
Maybe the lost dirt under the slab was the result of the pipe leak?

MAKE SURE to call out the cast iron plumbing. Note that it’s old and appears to be deteriorated, using your image as an illustration. We have a company town near here with lots of 1950’s slab homes. Many have had to replace the cast iron drain lines due to deterioration, like the deterioration you show from your pole camera image. It’s a costly repair.

Or the reverse…

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