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Foundations for porch

Discussion in 'Building' started by TullioK, 20 Oct 2020.

  1. TullioK

    TullioK

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    Hello,

    I would like to build a porch on the front of my house and while I'm comfortable enough with the walls and roof, I'm not sure what foundations I should be building on.

    At the moment there is an old concrete slab around the front of the house, this has got a large crack near to a manhole, but not where the proposed porch will be. I've seen some steel foundations bases with adjustable feet that sit on top of concrete, but they seem too good to be true. Do you think these would be suitable here? The walls will either be studs or I'll use one of the UPVC porch kits.

    If not a steel base on the existing concrete... what should I do instead?

    Whatever I go with, I'd like it to stay strong if in the future I ever decide to break out the rest of the concrete slab and resurface it.

    Here are some photos of the area and outline of the proposed porch shown in red.

    https://imgur.com/a/jo1lx3y

    Thank you
     
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  3. johnny2007

    johnny2007

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    When anyone asks about fundations, I always suggest to seek assistance from a very knowledgeable member who suggests to build whole houses on 200mm concrete.
    So for your porch a sheet of aquapanel should be more than enough...

    Unless you want your porch to stand there until you die, in which case you need to lift a bit of that concreye and dig down to see what's there.
    If it's solid rock (unlikely given the crack) you need very little done.
    If it's mud for half a meter, you need a different approach.
    In other words you need to investigate your base before making a plan.
    Let us know.
     
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  4. Ian H

    Ian H

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    Do your drain pass under where you are putting the porch?

    I would dig down to good ground, pour a concrete foundation, brick upto the level of your rendering then build up off that.
     
  5. ^woody^

    ^woody^

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    You can't build on that concrete nor but a frame on it

    Dig a trench 450mm wide by about 600mm deep and if the ground is firm, that's your foundation depth.

    Fill it with concrete up to 75mm below the ground level and then start the wall.
     
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  6. johnny2007

    johnny2007

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    600mm deep???
    Are you mad???
    Someone who knows (f@ck) all here on the forum, builds houses on 200mm concrete!!!
    Must become a professional cheap skate bodger.
     
  7. ^woody^

    ^woody^

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    Who is that?

    Foundation depth and thickness of concrete are distinct. So the OP could have 200mm thickness of concrete in a 600mm deep trench if he wanted to.
     
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  8. kingandy2nd

    kingandy2nd

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    Dude... let it go.
     
  9. Notch7

    Notch7

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    Johnny you are getting confused between the distance from ground level to bottom of trench and thickness of foundation.

    There are 2 main things which determine a foundation requirement: the load bearing capacity of the ground and it's stability.

    Sub soils from around 600mm to 1000mm, in suitable load bearing ground will most likely have suffient load bearing capacity for building on.

    A strip foundation of concrete 200mm thick may well be sufficient to build on.

    Not many builders use strip foundation construction anymore, it's more convenient to mass fill the trench and build off that......concrete is cheaper than labour and bricks.
     
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  11. denso13

    denso13

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    How I've always done it if the ground is suitable and always to NHBC and building control satisfaction.
     
  12. johnny2007

    johnny2007

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    So the question comes natural.
    You are building your own detached house, dug down to solid ground (let's call it 600mm for simplicity), would you pour 200mm concrete and build from there?
    Assume money and time are not a problem...
     
  13. ^woody^

    ^woody^

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    I did more or less that on my extension. It was easier and more expedient to pour a shallow strip in the bottom of a 1.2m deep trench and then bring the footings up in trench blocks, than it would have been to mass fill it.

    Other jobs get mass filled. It all depends.
     
  14. johnny2007

    johnny2007

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    You haven't answered the question.
    Would you build your detached house on 200mm concrete?
    And are you sure you only used a 200mm shallow strip on your extension?
    Or was it more like 300mm/400mm?
     
  15. denso13

    denso13

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    Yes, I did. And loads more.
     
  16. johnny2007

    johnny2007

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    Good on you!
    Give us a list in case we happen to buy one of them and end up with cracks everywhere...
     
  17. kingandy2nd

    kingandy2nd

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    Like I said before @johnny2007, let it go...you’ll give yourself an ulcer.

    I think I remember the original thread where you and @noseall fell out. That was about a porch too.

    Anyone heard from @noseall lately? Not seen him answer much lately.
     
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