Footing Depth for extension

Discussion in 'Builders' Talk' started by richo106, Aug 30, 2018.

  1. richo106

    richo106 Member


    Currently considering whether to convert single storey extensions to a double storey. I believe the footing depth needs to be 1m (correct me if im wrong)

    So i began to dig down to check the depth of them however i have 8 lines of brick below surface level before they sit on concrete. Is this normal? Also what is taken into account for footing depth? Just depth of concrete or bricks below surface and concrete?

    All help and information appreciated

  2. stuart44

    stuart44 Screwfix Select

    If it's an older extension it was was probably about 9 inches of concrete and a couple of feet of brickwork to ground level.
    The foundation depth is the depth of the trench when dug out.
    Ground conditions dictate what the depth should be, so it depends what your BCO says, but 1 metre is often enough.
    It can be more with certain subsoils and presence of trees.
    blarblarblarblar and KIAB like this.
  3. stevie22

    stevie22 Screwfix Select

    Building Control will normally accept an existing foundation even if not as deep as a current design would be. Worth asking.
  4. Isitreally

    Isitreally Super Member

    How old is the existing extension.??

    You will probably have to dig a test hole down the side of the existing foundation so the BCO can see whats what.

    I've only done two conversions to double story from single and both times the existing foundation was deemed to be ok, both were around a meter deep.
  5. sospan

    sospan Screwfix Select

    What has happened previously for me, is that as part of the pre planning application there are some outline plans drawn and we arrange a site meeting with the architect, BCO etc. They come along discuss the plans and look into a couple of holes dug around the foundations and then decide if they are fit for purpose, need some calcs from an SE or aren't suitable to support the new structure

    If the foundations aren't suitable the project either gets canned or on the rare occasion the whole thing gets demolished and started from scratch as its often much cheaper to do this than try and underpin

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