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Passing Sewer Line Under Footing - Permissable?

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  1. #1
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    Default Passing Sewer Line Under Footing - Permissable?

    I am excavating out ground floor rooms in my property to create a 2.4m ceiling height. The rooms include an internal toilet/bathroom which has to be released to the outside.
    To release the I have to have lower sewer lines which if I put in normally would cut throught the concrete edge beam below the brick veneer.

    Is it permissable to have a sewer line run beneath an concrete edge beam to enable a
    sewer line to be released from an internal bathroom? Or is this not permisable under building or plumbing codes as the pipe could either be crushed by edge beam or weaken the footing.

    Any experiences appreaciated.

    Cheers Plodder.

  2. #2
    1K Club Member Pulse's Avatar
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    If you went through the edge beam, It would be usually be designed deeper to allow for the penetration, also needs 25mm of compressible lagging material around it. Going under would undermine the footing and could not be done without some underpinning and probably engineer advice. You need 25mm clearance between the footing bottom (concrete) and pipe and need to cross at less than 45 degrees. The underpinning wouldn't be too hard, just excavate a pad either side of planned crossing point,slightly under the existing footing with a reinforced bridge beam cast between the pads, spanning the pipe (well padded) Be sure to chemset or grout lots of reo to tie the underpinning to the existing edge beam. Safer to also prop the wall above depending on what it is.

    Cheers
    Pulse

  3. #3
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    You can run it under or through (Between the mesh), no problem just make sure you lag the pipe where it passes through the footing. No need for anything else at all.

  4. #4
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    Guys,
    Thanks for feedback. Sounds as if going through the footing will be a lot less complicated than doing under pinning. 100mm pipe crosses perpendicular so no problem with 45Deg if I punch through the footing. A 100mm verandah slab rides on top of the single brick skin sitting on the footing, I'm assuming this is not an over heavy load for a footing (depth unknown expecting 2-300W and 3-400mm deep).

    Eastwing - when you say between the mesh does that mean the hole should be located through the mid-point of the footing? Does higher lower matter that much.

    Whats the best way to cut a 100+mm hole in a beam? Small rotary hammer?

    What is lagging and how much space around 100mm should I allow (i.e how big
    should the hole in the footing be?

    Cheers Plodder

  5. #5
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    The best way to go through is a diamond core drill, cheap ones are on Ebay but it may be better to get access then get a concrete cutting crew to core drill it. You should be safe going midway so you don't cut the top or bottom trench mesh which should be about 50mm from the top and bottom. AS3500 speciifies 25mm lagging as mentioned so hole should be about 160mm in diameter.

    Cheers
    Pulse

  6. #6
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    Put your pipe through the footing prior to pouring, wrap it in two thicknesses of foam expansion joint. Be sure it doesn't move around while pouring your footings.
    Plumbers were around long before Jesus was a carpenter

  7. #7
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    Guys, do the maths. the footing is estimated to be 400 deep. You have reinforcement top and bottom and if your right 50mm coverage is required from the top and the bottom of the beam. The 50mm coverage also applies between the steel reinforcement and the sewer line. Therefore you need 100mm concrete top and bottom + thickness of reinforcement = 200mm +. Then your asking for 160mm hole for the sewer line to allow for the lagging, that only leaves 40mm for tolerances. Also not much footing left. I have not been around as long as the plumbers only picked up my apprenticeship after Jesus came on the scene, but the first thing I would do is ask a plumber what depth is the sewer line outside of the building line so I know what level the new sewer needs to achive. Then before I go cutting through or digging under the footing I would seek advice from a structural engineer. Those guys walk on water.
    Good luck

  8. #8
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    Hoppy,
    I think your advice sound.
    I do have the option of going under the footing as the shaft to main sewer line outside is deep.
    This will also give me better fall 5:100 from inside the house to the sewer (I need at least 1.65:100 according to my readings of AS3500 code).


    The AS 3500.5 Plumbing and Drainage pt 5 Domestic installations says:

    4.15.2 Drains in proximity to footings and foundations

    Drains in proximity to footings and foundations shall comply with the

    following:
    (a) Drains shall pass under a strip footing at not less than 45 and shall
    have a minimum clearance of 25 mm from the top of the pipe to the
    underside of any footing.

    The full code adds:

    AS/NZS 3500.2:2003
    3.8.2 Installation near and under buildings
    (e) Requirements for pile systems shall be determined by a suitably qualified expert as recognized so by the jurisdiction having authority.

    So in short - yeah you can take it under and need engineer to design support for pipe.
    In the US I have seen posts about reinforcing arches under the footing to take the load around the pipe. My intent is to take it through the middle of a sliding door area were the lintel will carry the load to the edge of the doorways and therefore no load on pipe below footing.

    Attached is my little diagram of the setup with the proposed new drain line in blue. Does this look feasible?

    Cheers Plodder
    Attached Thumbnails Attached Thumbnails sewer-line-under-footing.jpg  

  9. #9
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    looks great, some sort of reinforcing arch was what I was banging on about in my first post,

    Cheers
    Pulse

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