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Foundation Drain Below Footer?

user-1146678 | Posted in General Questions on

Dear experts

here’s a quick question.
Old house 1920s, 1″ slab not really leveled must have been installed later. Thinking about removing all of it and redo.
Cylinder block foundation walls.
Now the guy who put the floor decades ago dug down to the bottom of the footer to increase head space. My understanding is the floor has to be above the footing but that would reduce space by 6 in turning it into a crawlspace.

I want to install a foundation drain to keep basement dry.
House actually not built level, it’s about one foot higher (!) on one side so water flows downhill won’t need to do much about that. Funny enough you can’t see it until you use a laser level….

But digging under the footer about 6 in to install the pipe and gravel sounds kind of risky to me. Yes I feel I should use the word stupid but I leave this up to you 🙂
Btw, doing this on the outside would also be same problem wouldn’t it since the floor indoors is lower than the footer?
As water seeks the lowest point, it naturally ends up on and under the floor inside 🙂

What should we do about it? Ideas/comments welcome

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  1. keithhoffman22 | | #1

    I'm just a diyer but it is my understanding the a cone descending at a 45 degree angle from the footer edge should be disturbed as little as possible. Unless you have a structural engineer tell you otherwise, I would be very reluctant to dig under or adjacent to my footer. You can probably find a local engineer to site visit and consult for an hour or two of billable time. That could be money very well spent compared to damage the soil support of your footer. In case you don't know this either, as I understand it ... once soil is disturbed, you cannot simply put it back and have it bear weight. In other words, once you disturb the earth under or adjacent to your footer, there is probably no going back.

  2. peaceonearth | | #2

    Defintely a place to be careful, as Keith stated, although I did something like this some years ago without perhaps being adequately aware of the dangers. I wanted a slab in my then dirt floor cellar, and also wanted more headroom. I dug inside the footings, -not under them, but kind straight down from the side of the footing. I was attentive to the gravel underneath being compacted and not falling in and undermining the support of the footing, which is what happened. I then added interior forms that surrounded the old footings, -going down further by 6-8", and ending up above old footing. The result was surrounding old footing with a new, interior only one that was also like a retaining wall. I then added drainage to a sump pump hole, poured a slab which is below the level of the old footing (using gravel from digging deeper). I do not appear to have any problems resulting, and it has now been about 12 years.

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