Recently uncovered this large (~1x1x12 foot) hole next to the foundation of my 1960s house in Minnesota. There’s framing that goes all the way down but nothing else seems to be in there. What is this? Can I fill it in with dirt or concrete?

Thanks for the responses on this mystery. I couldn’t comment on my own post due to being new so here are some responses.

There’s nothing at the bottom of the hole other than dirt. The basement is mostly finished. There is a storage room on the side of the hole with the red wire. We get water in there each spring but the finished portion of the basement has drain tile. Regarding it potentially being for radon, when we moved in we did install a radon mitigation system so if this was for radon it’s now obsolete. The previous own of the house has passed away and I have no method to contacting his children.

enter image description here

  • 4
    People usually do not build something like that for no reason. The reason might not be needed anymore, but I would like to know the reason before filling it in. Is there anything inside the basement?
    – crip659
    Sep 27, 2023 at 11:54
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    The architect or builder may still be alive. Any chance of asking them? Could it be a stormwater sump? If there is any moisture in the basement is it mainly near this location?
    – jay613
    Sep 27, 2023 at 13:09
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    Shine a light down there, or tie a bright light to a rope and lower it. This picture just shows the top of a hole, not anything about what's down the hole, which you'd need to know before choosing to fill it. I guess at that size you could fill it with something easily removable, like big hunks of styrofoam...
    – Ecnerwal
    Sep 27, 2023 at 14:31
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    You have managed to create two users. Please ask a moderator to merge them, or decide and use one only. Sep 27, 2023 at 15:07
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    Another idea, it could be for a sump pump that is lowered when needed
    – Traveler
    Sep 27, 2023 at 18:04

1 Answer 1


My great grandomthers house had something very close to that and I bet it's the same or similar. First I took your image and increased exposure:

enter image description here

The framing appears to be complete on the external facing and spaced evenly on the foundation side just like my grandmothers. Hers was made of cedar which it appears like yours may be as well.

For her house, she had a small pot belly stove downstairs serving the dual purpose of heating and cooking in case of a power outage. The vent pipe was ported into that channel, up, and out. Cedar was chosen by my great grandfather for its heat/fire resistance and because it's a natural insect repellant.

Personally, I wouldn't fill it in unless it is causing you problems currently. Foundations are complex creatures. If you fill it with cement, you could inadvertently cause erosion issues around the area and potentially weaken your foundation in the long term. On top of this, if any type of mast is ever erected that needs to be braced to the house, using an existing hole is always better than digging a new one.

  • 1
    When was your great grandmother's house built? OP's is "1960s" and while I love this answer, it seems unlikely a 1960s house would be built with a cedar-lined flue for wood-fired basement cooking and heating. I can see that kind of thing being advertised as a feature a hundred years earlier. Also, OP's is 12 feet deep. Surely far below the bottom of the foundation. Why would a flue well be that deep?
    – jay613
    Sep 30, 2023 at 12:16
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    Construction started in 1950 the year after my grandmother was born, I think it took him 2 years to build. To be fair, I'm from the rural foothills of NC, US... Many homes around here still have pot belly stoves or at a minimum some sort of auxiliary fireplace. I could see the same being true in Canada for the winter. As for depth, maybe OP has a split-level home with a lower basement, otherwise I can't explain the depth. The one at my great grandmother's house went 6 inches below the basement floor... Though I never really thought about why until this very moment. Sep 30, 2023 at 13:06
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    @user174430 examine the basement walls adjacent to this shaft, and use a camera and light to examine the walls of the shaft, for remnants (maybe closed up) of any former holes. Maybe for venting a burner, or maybe a smaller one for (see my suggestion above) antenna cable.
    – jay613
    Sep 30, 2023 at 16:35
  • @jay613 Good idea. While you're down there, it's also worth looking at the very bottom of each side for cylindrical stress marks. If someone had a Ham radio antenna with a backup DC ballast (Not sure if that's the right phrasing) or linear amp coil at the base it would be easy to identify. Sep 30, 2023 at 16:44

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