Footings in chalk

Discussion in 'Building' started by baldy01, 21 Sep 2006.

  1. baldy01

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    Hi all,

    I'm new here so hello to everyone, hopefully this is a simple question to answer.

    I'm putting in footings for a conservatory, the soil under my house is chalk and its only about 6 inches down. If I have solid chalk to lay my footings in do I really need to go to the regulation 600mm deep? I was intending to use a 450x250cm foundation, that extra 350mm is an extra 5 layers of subsoil brickwork for what actual gain? My plan was to dig down far enough to bury my footings and maybe 1 brick subsoil giving about 350mm from soil level to the base of the footing. As long as its all dug down to solid chalk shouldn't this be ok? One wall will be a single story high end wall, probably a cavity wall.

    Cheers

    Pete
     
  2. Static

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    There are no regs for conservatories, so simply you can do what you like as its a temp structure.
    But if you want it to last more than 5yrs then i would at least attempt to go below the frost zone.
     
  3. baldy01

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    So the depth is to keep the concrete footings away from the frost? That does make sense, thanks.

    I've read that a cheaper alternative to the extra subsoil brickwork is to fill the trench with more concrete. Can you tell me if this should be done as a separate operation to the basic foundation layer, i.e should you let the 250mm footing set before filling with more concrete, as you would let it set before bricklaying?

    Thanks again for the help here, I'm in research mode as I like to ask the stupid questions BEFORE I get myself a mess!

    Pete
     
  4. gardeners26

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    On Epsom Downs I also have solid chalk under only a few inches of soil. After ten years of building numerous structures with 'only' ten inch concrete foundations directly onto the chalk non have yet showed any signs of movement,cracks or failure.
     
  5. Static

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    Trench fill is done normally in one pour to the level you require. Remember to sort out levels of any drainage you have first
     
  6. baldy01

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    Nice one, thanks guys.
     

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