footings and foundations

Discussion in 'Buildings & Infrastructure' started by Neddy flanders, Feb 11, 2019.

  1. for a small single storey house extension.
    walls are 4" brick and 4" block with insulation in between.

    if trenches are 450 or 600mm wide and 900 deep, how much concrete would you tip in the bottom (it will have steel in it)?

    when you fit the soil pipe through the wall from the toilet position, does it usually go through the concrete or through the blockwork below the DPC?

    is FFL inside usually above or below DPC or same as?

  2. Derky

    Derky Member

    Standard would be 450 wide 600 deep. No steel. Then blocks on top with your soil pipes and services going through these blocks. You need a lintel on top with pea shingle around them so they can move. Concrete around them in the cavity will be frowned upon by B/C.
    DPC will be above sub base which is blinded by sand then concrete on top. Then your celetex and final floor screed.
    Make sure the top of the footing works with your brick courses on the existing so that once up through the ground it all ties up on the same level.
    Lofty1984 likes this.
  3. bobk

    bobk Member

    At least a foot or 300mm , like derky says concrete lintel over soil pipes
  4. thanks, so does it matter if FFL is above or below DPC slightly?
    lintel and pea gravel makes sense, but soil pipe will be concreted into floor slab so fixed solid??
  5. bobk

    bobk Member

    DPC has to be under the concrete floor 2 layers of it , or 4 inches
  6. bobk

    bobk Member

    And above the 100mm kingspan you've installed
  7. nick...

    nick... Member

    south norfolk
    Depending on soil and building control,south norfolk council like a metre deep trench and 600 wide.most people trench fill nowadays unlike in the past when everything would have 9inches of concrete and then blocked from there.may get away with 600 dig in sand but never in Clay and sometimes deeper still.dont plenty at 6ft deep and deepest I’ve ever done was 14ft beside a tree which was ridiculous but that’s what council demanded.can also pile to save some money in unstable ground
  8. bobk

    bobk Member

    And you wonder why houses are so expensive .
    nick... likes this.
  9. David.

    David. Member

    J11 M40
    I should think it's cheaper to come up to ground level with a metre depth of concrete than to fart about down a hole, laying trench blocks nowadays. Labour comes to more than the materials.
    BobGreen likes this.
  10. bobk

    bobk Member

    Then you have to put a raft in .
  11. tancoman

    tancoman Member

    This is a small single story extension that is being built. You need only 12" deep of concrete in your foundation. Width is more important than depth. The type of ground under the foundation is most important, if its not solid all the concrete in the world wont cure it.
  12. Bongodog

    Bongodog Member

    I think Neddy is referring to the DPC in the brickwork, not the oversite as others have assumed. The dpc in the walls is usually around 25mm above finished floor level and should be directly behind the skirting boards and not covered with plaster.
  13. bobk

    bobk Member

    And what's the point in that ?
  14. Foxcover

    Foxcover Member

    Currently building a workshop with a washroom at the moment and also wondering how you surround soil pipe with gravel if it’s concreted into floor slab?
    Neddy flanders likes this.
  15. agrotron

    agrotron Member

    Dpc is usually at floor level. The ffl internally is minimum 6inch higher than extenal ground level.

    You can mass fill the footing with concrete, and put the soil pipe within the concrete but connect up either side of the footing with rubber collar to allow a bit of movement.
    Foxcover likes this.
  16. Bongodog

    Bongodog Member

    Otherwise the plaster bridges the damp course making it useless

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