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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018
     
    Afternoon all!

    This weekend I started having an exploratory dig where the first part of my footings are going and came across a couple of soil pipes. By my measurements, they narrowly miss where the wall is to be built but don't allow enough clearance for the 150mm all around. My understanding is that in this scenario, I need to remove all the concrete encasing the soil pipes and dig down under them to an additional depth of 450mm. I imagine after that, I'll build up to damp course and encase the pipes back with shingle. I've done a crude drawing to aid in expressing my situation, the black line is the existing house, the red is the proposed footing shape, the blue is the wall form and the orange is the clay pipework. Any advice or guidance would be greatly appreciated!

    Kind regards,

    Adam
      Image1.jpg
    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018
     
    Photo of the current situation, don't you love chalk!
      20180304_113041.jpg
    • CommentAuthortony
    • CommentTimeMar 5th 2018
     
    If it was me I would leave alone completely the straight pipe. Very carefully remove some concrete from the diagonal pipe but only near the corner of the new construction.

    I would make the footing 300mm longer to compensate for leaving the straight pipe.

    I would not dig down very much under the pipes like 150mm should be OK.

    I would separate the footing from the pipe/concrete with bubble wrap or polystyrene .

    And yes I love chalk, the inspector should too.
    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018
     
    Thanks Tony,

    As the diagonal pipe is cased in a mass of concrete splaying at 45degress either side, I was going to remove it all on the left hand side to avoid any potential load being transferred on to the pipe.

    I must admit I'm quite surprised that 150mm deep footings would be enough for a 2 storey extension?

    I'm assuming that by longer you mean bring further down towards the bottom of the page?

    Thanks again,

    Adam
    • CommentAuthortony
    • CommentTimeMar 5th 2018
     
    In chalk it would be enough, but I meant 150 below the bottom of the pipe trench and to whatever thickness is being called for.

    It might surprise many to learn that substructure can safely be corbelled out over things like pipes even on external corners.
    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018 edited
     
    Tony,

    Hopefully I wont have to result to corbelling but its good to know should I need to!

    I think I understand your design now, that's reassuring as I dread the though of having to dig out any deeper in that chalk!

    I've created a child-like sectional view of my interpretation of your design, does this look right to you?

    Thanks,

    Adam
      Image2.jpg
    • CommentAuthortony
    • CommentTimeMar 5th 2018
     
    looks good, you must use soft material, eps/bubblewrap where pipe is trying to be in contact with the substructure

    Not sure trench fill is the right way to go
    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018
     
    Tony,

    Could you explain what you mean by 'trenchfill' please? What are the alternatives?

    I have plenty of bubblewrap and PIR offcuts laying around so that shouldn't be a problem.
    • CommentAuthortony
    • CommentTimeMar 5th 2018
     
    the black line in you pic represents trench fill as opposed to filling only say the bottom 250mm of the foundation trench = strip footing
    • CommentAuthoradam_w
    • CommentTimeMar 5th 2018
     
    Ah I see but strip could potentially result in a deeper strip in order to meet the required footing depth? I guess that sort of decision would down to the BCO? He's coming Friday but I feel much better equipped to discuss these matters with him now :)
    • CommentAuthoradam_w
    • CommentTimeMar 13th 2018 edited
     
    Building control Officer came Friday and he was happy with the footing once I cleared out the surrounding concrete. He's also given me permission to mix and fill the void myself. So aiming at a C25 strength, what is the best way to ensure consistency of mix ratios? I think C25 is around a 5:1 ballast mix, so would the 'bucket' method be accurate enough or would 5 bags of ballast and one bag of cement be sufficient?

    Thanks in advance,

    Adam
    • CommentAuthortony
    • CommentTimeMar 13th 2018
     
    Shovels
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