What's this 'hole' in my basement?

In My Humble Opinion
1

First off, this is a sub-grade basement on a slab, no crawlspace.

Here’s a picture. It’s tough to see there, but it’s that rectangle, sort of half under the fake Christmas Tree. Not that this helps that much, but you can kinda see from this picture that the ‘hole’ is under the stairs and in the path from one area of the basement to another, so putting something there would be in the way. Of note, the plans for the house call for the the floor drain, the HVAC equipment and the sump pump to be where they’re currently located to I don’t think it has anything to do with any of those. Also, from what I’ve seen, sump pump pits tend to be round, not rectangular. Further, if it makes a difference, this hole measures out to some exact number, I don’t remember what, but something like 18x24, which tells me that a form was put in place before the slab was poured, not that it was chipped/jackhammered out afterwards for one reason or another.

Skipping all the obvious jokes, any ideas? The only thing I’ve been able to come up with, that makes any sense, is that the inspector gave them the go ahead to pour the concrete, provided they leave a spot open so that it could be inspected for mesh/rebar/vapor barrier and/or they (builders/engineers/inspector) wanted to be able to see what was under the concrete so they could keep moving forward on building before it was singed off or they (the builders/engineers) wanted to see if it filled with water to decide how to handle the sump pump/drain tile situation.

It’s the only one I know of in the basement, unless there’s another one under the small carpeted area.

Just to reiterate/mention: All the mechanicals are where they plans call for them to be. The plans don’t mention anything about, say, a bathroom in the basement. If something was in that spot, it would really be in the way. There’s a plumbing clean out near where the plumbing leaves the building (which makes sense). Maybe the plumbing goes under that spot and they had to do something with it?

Honestly, I have no idea about this and from time to time it bugs me, mostly because I can’t figure it out.

One last thing: the plumbing and electrical come in through the wall (well below grade) so it’s (probably) not that. Also, from what I can remember, all the drains are stubbed in where the plans call fro them as well as being stubbed in and the concrete poured right around them (as opposed to doing something like this.

2

Sanitary sewer back up valve.

3

+1

The pipe running across that hole is your sewer line.

4

If it was a backup valve, there would would be an access port for cleaning and maintaining it.

I’m not sure what pipe you see running across the hole.

5

I’m not seeing a hole. Are you talking about the rectangular thing in front of the tree (direction of picture taker)? If so, it looks like a discolored portion of the slab…maybe a slight depression to it.

If it is the dark area behind the tree, I cannot make much out.

Is there no way to get a better picture of what you are referring to?

6

I had a hard time getting a better picture of it when I tried. It is discolored and maybe ever so slightly depressed, but it appears to be a different mix of concrete* (from what I can recall, I’m not at home right now) and as I said, it’s a very specific size with 90 degree angles. This was made with forms so it’s not like they poured the entire basement and it’s just a low spot with an odd shadow.

*My WAG is that after they poured the slab and did whatever they needed to do, this was just done with a bag of concrete and mixed on site.

7

Surely one would not pour concrete over a clean out?

8

Body parts? Hidden valuables?
:dubious:

9

That’s why I’m assuming it doesn’t have anything to do with the plumbing system*. The house does seem to be built pretty well. In fact, when I had a roofing estimate done recently, the roofer mentioned that it was clearly planned by an engineer.
*Short of some kind of problem, say, the cement truck was backing in but they needed to add a coupling to attach two sections of PVC. Concrete guy is tapping his watch, foreman is on the phone, the guy is at Home Depot…so they just form around it, do the pour, and fill that section in later. But that seems a bit far fetched.

10

I’d assume something to do with the plumbing. Seems unlikely for a house basement but you might see something like that if the slab was prestressed concrete. That’s where the rebar would have been welded together to stress it, then cut apart after the concrete set. Other than that it’s most likely a gateway to Hell so I wouldn’t try digging it out.

11

Might have been a hole for a sump pump at one time; somebody decided the pump wasn’t necessary, removed it, and filled the hole.

12

What would be under a sump pump? Perhaps a space for water to collect.

13

If that is a filled-in sump pump hole, the pump would have been at the bottom of the hole.

Joey, might that rectangle be near an electrical outlet?

14

The sump pump is located exactly where it’s shown in the plans I have for the house. Also, the house was built in 97 and I bought it from the people that ‘built’ it. It’s unlikely that they had the sump pump put somewhere else, then moved to the ‘correct’. Besides, wouldn’t that be a round hole, also, if you remove a sump pit, you’d have all that drain tile leading to it…seems that would be a problem.

I almost wonder if it’s the beginnings of an abandoned bathroom. The plans don’t call for a bathroom in the basement, but maybe they asked for one to be added on (under the stairs? in the way?) so they started going in that direction, then changed their mind, but at that point, you’d think they’d still leave the plumbing connection above the concrete, just for future use.

15

Square holes aren’t unheard of. I checked before bringing it up.

16

Just for some more context, here’s another quick picture. In this picture you can see the ‘hole’ right in front of that fake tree, directly under the stairs. Now, directly past the hole is a floor drain. Behind me, against the back wall of the basement is the (only) clean out for the plumbing system, but it should also be noted that rising up, behind the water heater is the main stack that handles all of the plumbing in the house. One would think that the floor drain goes that way and connects to it, but from what I can see, it does go down and heads towards the hole. Of course, that’s just the trap and I have no idea at all what happens after that and where it connects to the main drain.

So, that does push this more in the direction of it having, at least, something to do with the drain, but it still doesn’t make sense. All the PVC drains are ‘stubbed in’ with the concrete poured around them, nothing has a giant rectangle formed around it. I still have to wonder, if it is plumbing related, that maybe they were thinking about putting a full bathroom there. I recall when I bought the house, the owner said the original (cookie cutter) plans called for two full bathrooms on the first (it’s a one floor) house, but she opted for 1.5 bathrooms since the half bath gave her space to put a pantry in the kitchen. Maybe there were thoughts of putting it in the basement. But that just seems like a terrible location (in what was, at the time, an unfinished basement), and besides, why wouldn’t they leave the plumbing exposed for possible future use.

I’m also confident the previous homeowner didn’t fill this in himself. He did plenty of work around the house on his own and it’s sloppy. If he filled it in, there’d be concrete splattered all over the floor, the underside of the stairs, his kid’s initials in it and, I can almost guarantee, his tools and/or garbage would have still been down there when I moved in. I’m fairly certain it was filled in by the builders.

Perhaps we’ll never know.

(On preview, I should add, because it was asked about, that blue box you see, it’s not an outlet, it’s a phone jack).

17

How deep is the hole, about 0.25"?

18

Not sure I have any way (short of drilling it) to find out. The plans say the slab is 3", but that’s all I got, they don’t show any kind of hole/appliance/fixture/plumbing etc there. Granted, they’re building plans, not electrical or plumbing plans, but they do give a rough idea as to where major things (drains/switches/lights/sump pump pit/furnace etc) will be located. No mention of this.

PS, just so we’re on the same page, I’m not going to start hacking away at the slab to see how deep this is.

19

NETA, one thing I can think of is a floor safe. It’s VERY common to put floor safes under your stairs (though usually much further in than this) so that a would be robber has a much harder time swinging a sledge hammer at it. However, again, (in addition to it not being far enough under the stairs), it’s still a project that appears to have been both started and abandoned during the building phase.

20

Typically that type of patch in concrete is because a pipe below it needed to be repaired.

If it is a new house, it could also be due to a quality problem with the concrete which was there. Maybe a dog or kid walked in it? Then they fixed it.