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Extension Foundations, Clay and piling

Discussion in 'Building' started by burts, 10 May 2019.

  1. burts

    burts

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    I have full plans for an extension and conpleting on a building notice. I dig a trial pit for inspector, turns out my house and garage foundations are on piles. I have clarified with original drawings.

    Piles is simply not an option as it’s far too expensive. Inspector suggested a soil examination, but they are around £1600 themselves. Anyone suggest any ideas. Are raft foundations suitable and generally accepted?
     
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  3. acurachris

    acurachris

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    The house and garage are likely built on piles because the ground wasn't good enough for standard strip foundations; it makes sense to pile the extension if your house is, IMHO.

    Have you had a quote for piling?
     
  4. burts

    burts

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    Yes I’m aware that the ground probably isn’t as good as it could be, it’s high risk of shrinking.

    Lots of builders keep suggesting a raft.

    I had a quote based on my house footprint as the extension is the same size and by the time all extras were thrown on. Groundbas, Rebar, heaven protection .... was all about 15k.
    7 x 4 metre extension. Ridiculous.
     
  5. acurachris

    acurachris

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    That does sound ridiculous, I’d get a couple more quotes, on another post today, notch7 was saying how he did a piling job in the south east, approx 6x6m for about 9k + vat
     
  6. burts

    burts

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    To be fair 10k will still make me not go ahead. I’m a tradesman and was only doing it because it’s minimal labour for the rest of it.

    It’s so annoying because Grundomat piles look ridiculously easy to do.
     
  7. ^woody^

    ^woody^

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    Thats the problem. The money you should have spent on having it properly designed, can now go instead on advice from a structural engineer.
     
  8. burts

    burts

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    The extension is going between 2 garages both with piled foundations. What about steels bridging the foundations ‍♂️
     
  9. burts

    burts

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    And how would that have helped me? So if I spent the £900 on having someone investigate and design it .... then still have to pay for the piling. ....
    Building notice is refundable if works don’t start.
    Makes no odds if I had someone design it.
     
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  11. Notch7

    Notch7

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    A raft may be possible especially if its a single storey. The problem is that the extension will float around on top of the soil, wheras the house will stay sat on its rigid stilts.

    In reality it means there may be some movement where the 2 join. If you can live with making this a flexible joint, say with an architrave trim or accept a bit of plaster cracking, it should be fine.

    Not all builders can do rafts, or do them properly. Damp arrangements can be tricky. You will need it designed by an engineer, it will require reinforcing steels specified and a bending schedule. If you have good access, that will help as you might need 500mm depth of type 1, so bulk delivery and muckaway will save you money.

    A raft means you wont need a block and beam floor. Also on a 7m x 4m extension, its likely it will need to be made in 2 bays with piles in the middle -although concrete beams are available that length, but they are the extra deep ones and massively heavy.
     
  12. ^woody^

    ^woody^

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    They would have designed an alternative to piling if you can't afford piling. And you would not have wasted the time applying for planning permission for something you can't afford to build.
     
  13. Ian H

    Ian H

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    Can you DIY them? It looks just like the Moling kits I hire from PSS (part of A-Plant) to replace water supply pipes.
     
  14. burts

    burts

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    Ok, I see your point with the designing an alternative. Thought you meant designed and still went ahead with piling.

    A structural engineer is not guaranteed to be able to find an alternative and then I’d have lost that money. This way I can gauge what the building inspector will deem passable. If they say piling is the only way then I will get my money back.
    Simple. Or I can still pay a structural engineer if they think an alternative would be possible with knowing the local area.

    And I can afford the piling, but like everything you weigh up wether the gain is worth the cost and it’s not.
     
  15. burts

    burts

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    I could DIY a lot of the work but Can’t find anywhere that hires the mini piling machine.
     
  16. burts

    burts

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    Yes I have the original drawings which isn’t the same footprint of the house. 3 piles up each length and 1 in the middle creating 2 bays as you mention.

    I only really need to do one length (new cavity wall) and one width (end of extension with bifold doors)
    Plan to incorporate the garage wall and just brick between the house and garage which is 2 meters.

    What would your suggestion be?
     
  17. Ian H

    Ian H

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