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Bridging clay sewer pipe

Discussion in 'Building' started by Marty79, 18 Apr 2021.

  1. Marty79

    Marty79

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    Good evening all! Just want to say that this site is fantastic and the knowledge within in immense. Until recently I've been able to find all I need from here without having to beg for info, but I just need some clarification regarding the footings that I'm going to pour for a timber framed side extension that I'm (hopefully) going to start within the next two weeks. Basically as it stands I've dug down a metre plus a further 150mm below the existing sewer pipe but I've been told by a builder friend that I have to dig a further 300mm down and then pour the 300mm of concrete to 150mm below the pipe, and then block/brick to above the level of the pipe and bridge with lintel e.t.c. as normal. However, I've also heard that I can just ply either side of the pipe (150mm spacing for shingle) and pour the concrete up to the required depth and then bridge as normal, and then up to DPC. Which is the correct approach in this particular scenario? If I have to go deeper then that's fine but I would rather not if the necessity isn't there. I'm no stranger to building works e.t.c. as I've pretty much rebuilt my house but this is something new to me and not exactly something that I want to get wrong. Any help on this matter is greatly appreciated. Take care all.
     
    Last edited: 19 Apr 2021
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  3. Marty79

    Marty79

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    I think I'm just going to dig down a further 300mm. The trenches are only 7' wide so it's not too much extra work. I'll try to return in the future with updates and photos for the project section. Take care all
     
  4. SpecialK

    SpecialK

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    Pretty sure its 150mm below the bottom of the pipe. Check the local water co's website there may be information on there?

    When I did mine I used shuttering either side and the concrete was poured to required level. A lintel then bridged the pipe / gap

    BC said void could be left but I backfilled it with gravel as it was 1.2m deep!
     
  5. Marty79

    Marty79

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    Thanks SpecialK. I'm currently 150mm below the pipe across the entire trench. I've had some conflicting info regarding the actual footing though, as various sources say that I can now just shutter the pipe with a 150mm space all round for shingle, pour concrete, remove shuttering then bridge with lintel. But a builder friend said I have to go down a further 300mm from it's current depth, and then pour the 300mm concrete and build up with blocks and lintel over e.t.c. Thanks mate. Have a good day.
     
  6. SpecialK

    SpecialK

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    Are building control involved? If so have a chat with them to see what they want.
    Otherwise just do what you think is best. 150mm or more below invert sounds good as the foundation weight will be under the pipe.
    You will need 18mm OSB and supports between if you are filling the entire trench with concrete...

    drain1.jpg

     
  7. Marty79

    Marty79

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    Thanks again Special. That picture looks pretty much identical to how my trench looks right now, only my pipe is about 800mm-1000mm below ground, and my trench runs straight just over 7ft wide between my house and the double skinned wall between mine and next door neighbour. They had their extension done a few years back and the double skinned wall was done for me to build to when I was ready. It should've been done last year but something strange happened around March time and since then materials e.t.c. have been difficult to obtain. Fingers crossed I can get it done this year though. I've got until September. Wish me luck
     
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