1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Foundations for my outbuilding

Discussion in 'Building' started by BasicBuilder, 20 Apr 2021.

  1. BasicBuilder

    BasicBuilder

    Joined:
    20 Apr 2021
    Messages:
    3
    Thanks Received:
    0
    Country:
    United Kingdom
    Hi all, I hope you are well. I'll try to keep this short.

    I am building an outbuilding (hopefully to use as an office / gym). The size is approx. 7m by 4m.
    It is being built on the boundary so within 1m.

    I plan to build it all of the light breeze blocks (except two rows of bricks at the bottom, for DPC I believe).

    My question is, how deep / wide should my foundations be?
    For width: planned to do these at 400mm (100m for 4" brick / block and 150mm each side remaining).
    For depth: planned to do 300mm.
    Then fill with 2" of hardcore and then rest with 1/3/5 (cement, sand and ballast).

    SPANNER in the works is that the neighbour on the back side of the shed has a big tree in his boundary. The roots of this are partially in my garden. Beneath where the shed will sit. I planned to do a depth of 600mm along this back wall to be safe.

    Any help would be much appreciated.
     
  2. Sponsored Links
  3. Scarlet Pimpernel

    Scarlet Pimpernel

    Joined:
    9 May 2020
    Messages:
    7,402
    Thanks Received:
    132
    Country:
    France
    I'm no expert, just a DIYer, but as no-one else has answered, I'll do my best.
    For depth, you need to go down to undisturbed ground and to ground that has nothing left to compost, e.g. clay, gravel, rock etc. In other words down past any topsoil, and at least 500mm deep to bottom of trench. But the ground conditions may determine deeper.
    I believe 300 mm wide is sufficient, but the ground conditions may determine different.
    Here's an excellent article:
    https://www.designingbuildings.co.uk/wiki/Strip_foundation

    You don't use hardcore in strip foundations.

    If you're doing minimum strip foundations, or trench fill foundations. you need enough brick courses to get you out of the ground, e.g. up to dpc level. although blocks can be used, it depends on your blocks, if they're OK to use below ground.

    To assess the tree roots problem, you may need to partially dig the trench to assess the situation and then seek expert advice. Maybe photographs, and a question on this forum.
     
  4. BasicBuilder

    BasicBuilder

    Joined:
    20 Apr 2021
    Messages:
    3
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for responding.

    I think this would be classed as trench fill foundations and I was advised to just fill it with mixtures of ballast, cement and building sand. Then do my a couple layers of bricks with DPC.
    Would this not be the best way then?
     
  5. Scarlet Pimpernel

    Scarlet Pimpernel

    Joined:
    9 May 2020
    Messages:
    7,402
    Thanks Received:
    132
    Country:
    France
  6. BasicBuilder

    BasicBuilder

    Joined:
    20 Apr 2021
    Messages:
    3
    Thanks Received:
    0
    Country:
    United Kingdom
    300mm depth as in the depth of the trench. Then maybe 50mm hardcore and 250mm of concrete as per the above mix.

    So I'd bring it to ground level and then put a layer of bricks with the DPC material above.
     
  7. Scarlet Pimpernel

    Scarlet Pimpernel

    Joined:
    9 May 2020
    Messages:
    7,402
    Thanks Received:
    132
    Country:
    France
    I'd advise 450mm deep, as long as the ground is good.
    No hardcore required.
     
  8. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
  9. Sponsored Links
Loading...

Share This Page