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Thread: Piping vs. Footing

  1. #1
    DIY Senior Member dlarrivee's Avatar
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    Default Piping vs. Footing

    I just finished sawcutting and smashing out a bunch of basement slab to run some new drain pipes for a bathroom renovation.

    I knew I would run into a footing underneath a load bearing wall, and that wall is where I wanted my 2" abs to come up to serve the lav and vent up all the way to the attic and then the roof...

    My question is this, am I crazy for chipping away at the corner of this footing to run the pipe, or is this common?

    I imagine if this was a new building and I was plumbing before the slab was poured, I would still have to chip away at the footing a little bit to make it work...



    You can just see the edge of the footing below the little bit of slab I left in place close to the wall. I put that fitting there just for reference as to where I want the pipe to come up.
    Last edited by dlarrivee; 11-07-2010 at 06:19 PM.

  2. #2
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    Is the vanity going to be located in the area where you need the drain? If so you could bring the drain line through floor before the footing, then offset it back into the wall in the toe kick space under the vanity.

    John

  3. #3
    Homeowner Thatguy's Avatar
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    Here's a start for the answer

    "Be sure to fill any notches in the footing"
    from
    http://www.concretenetwork.com/concr...d_footings.htm

    My concern would be that the uniformly distributed stress in the footing would be concentrated at the notches, causing cracks that would spread.

  4. #4
    Nuclear Engineer nukeman's Avatar
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    Wouldn't worry about it. You are removing a tiny area compared to the total area. For instance, I had to do this myself on a couple lines. The footing was probably 18" wide x 26' long (total bearing area of ~39 sqft). The notch that you are making is maybe a few square inches (~7 sq.in for an equivalent 3" circle). 144 sq.in per sq.ft. For my footing, this 3" hole would equal 0.125% of the total bearing area. If your soil vs. footing area is that marginal, you have much bigger issues.

    Other things to think about (many won't apply to your case):

    1. Typically, pipes cannot run parallel to a footing within a 45* projection from the footing downward.

    2. When running the pipe through a footing, poured concrete wall, etc., typically you'll need to run the pipe through a sleeve. Typically, the sleeve size must be 2 pipe sizes larger than the pipe you are running.

    3. If running perpendicular and under the footing, you are often required to have a relieving arch. This helps to move the load away from the pipe.

    In your situation, I would chip out what you need. I would come down at a 45* angle just below the bottom plate. This way, the pipe stays above the bearing area. This is better than going straight down and then having an elbow outward since that section of pipe near the footing would be subject to the load from the foundation. It would probably still be okay, but it is better to play it safe.

    I wouldn't be concerned about the notch forming cracks. The load isn't in the direction of the notch, so it is not really an issue. You could chip a rounded notch if you were still concerned.

    In my case, chipping the footing was real hard. The concrete is 42+ years old (hard and thick). The soil was almost as hard (clay that had been compressed for those years). Was not fun.

  5. #5
    DIY Senior Member dlarrivee's Avatar
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    I was planning on using 2 45*s instead of one 90* and only chipping away what I needed, is that what you're saying too nukeman? I have quite a bit of slab thickness before I even hit the footing, we're talking 4.5 inches.

  6. #6
    Nuclear Engineer nukeman's Avatar
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    That's exactly right. This will limit how much you have to chip and keep the pipe above the area of soil that is seeing the load.

    You could imagine the shear forces if you had a pipe running under the footing with no protection. The soil away from the footing would have no real load, but the soil under the footing would have the load. Over time, as things settle, one end of the pipe would be pushed down as the earth compresses and the rest of the pipe would not.

    In my case, the main existing line was fairly close to the footing (~12" away, parallel). I went vertically going into the slab and then went 45* ASAP. This pipe would continue down at 45* until you got down to the depth you needed and then add another 45* to go horizontal in your case. In my case, this distance was very short . I had to run the 2nd 45* fitting the other way to go vertically downward to catch the main.

    I may have a pic of want I did if you want to see.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Yes, and a 60 at the top would require even less footing removal, although it takes a little more skill to get it get it back to horizontal at the bottom.

  8. #8
    DIY Senior Member dlarrivee's Avatar
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    Interesting, thanks for all the responses. I was pretty sure I could make it work one way or another, but it's good to check now and then.

    HJ, if one were to use a 60 degree fitting where the bottom plate of the stud-wall is, would I end up using 2 more fittings to get back to horizontal as opposed to the 2 45* bend offset?

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