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Wall foundations depth

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  • 10-07-2006 2:53pm
    #1
    lemeister
    Registered Users Posts: 263 ✭✭


    I have to build a small retainer wall in my garden for a split level lawn and the wall will at very most be 16 inches high. How deep/wide would the foundations for this wall need to be? I’m planning to use 4’ solids on the flat to build the wall.


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    #2
    muffler
    Registered Users Posts: 46,130 ✭✭✭✭muffler


    Answers here :D


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    #3
    lemeister
    Registered Users Posts: 263 ✭✭lemeister


    :D Well spotted!:D


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    #4
    Sonnenblumen
    Registered Users Posts: 5,834 ✭✭✭Sonnenblumen


    If the wall is at near end of slope it is very important that you back fill at least 1/3 -1/2 height with dry aggregate (pea gravel) so as to prevent build up of water (can cause havoc during freezing periods) alternatively you can isert small cuts of 2" Water pipe along base every 6'0" or so to allow water drain away. A simpler alternative, but demands clean blocklaying is to leave 1" slits between every 4/5 blocks on first course.

    Re Foundations: 4" each side block (17-18" max) and 6" depth is plenty big on 3"-4" compacted Hardcore/Rubble for your requirements.


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    #5
    muffler
    Registered Users Posts: 46,130 ✭✭✭✭muffler


    lemeister wrote:
    :D Well spotted!:D
    Sorry about that but I couldn't resist it ;)


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    #6
    Dirk Gently
    Closed Accounts Posts: 4,784 ✭✭✭Dirk Gently


    as a rule of thumb, foundations should be 3 times the width of the wall and at least as deep as the width of the wall.

    eg. 300mm cavity wall

    foundation = 900mm wide by 300mm deep with wall sitting on centre of foundation with 300mm each side.

    45 degree rule is also a handy way of working it out. go at 45 degrees off each edge of the wall by the width of the wall. should end up with the same width of your wall each side of it in the foundation.


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    #7
    Mellor
    Registered Users Posts: 39,404 ✭✭✭✭Mellor


    clown bag wrote:
    as a rule of thumb, foundations should be 3 times the width of the wall and at least as deep as the width of the wall.

    eg. 300mm cavity wall

    foundation = 900mm wide by 300mm deep with wall sitting on centre of foundation with 300mm each side.

    45 degree rule is also a handy way of working it out. go at 45 degrees off each edge of the wall by the width of the wall. should end up with the same width of your wall each side of it in the foundation.
    The foundation should be at least as THICK as the width of the wall. And at a depth as least equal to the width of the foundation.

    A 300mm wall sits on a concrete strip 900mmx300mm which is at a depth of 900mm, or deeper if the ground is not suitable.

    I'm sure you knew this clown bag, this is more for anybody with no knowledge, dont want people miss understanding your post.


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    #8
    armchairninja
    Registered Users Posts: 323 ✭✭armchairninja


    The reason for the width is because concrete shears at 45 degrees. so make sure that your foundation is wide enough to allow for shear without jepordising the walls stability.

    And Personally I think you should build the wall a little bit thicker using the same method as used for footings, 1 block on side, 2 on flat, as it would lessen the impact of lateral forces, this would give you a wall of 325mm thickness

    Some might think that this is overkill, but as I always say its better to be lookin at it than barrowing it all back out to the front of the house;)


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