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void under beam & block floor problem..

Discussion in 'Building Regulations and Planning Permission' started by TheDeuce, 20 Sep 2021.

  1. TheDeuce

    TheDeuce

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    Hi all,

    We've recently had our foundations poured, unfortunately the chap that did it put the excess concrete in the area between the foundation beams, which is supposed to be our 150mm void. Picture below shows the over-spill of concrete that I estimate covers about 10% of the void area and at the highest points is no less than 100mm beneath where the floor beams will be.

    The question is, do we need to bother breaking it up and removing it to technically achieve a uniform 150mm void? Or can we leave it how it is and simply excavate the other 90% to the minimum?

    I'm asking because the conrete in question is far deeper and thus more solid than the photo shows - removing it would require a powered breaker which is an extra expense and hassle.

    Do building control even check this? Our officer said they would next visit once the floor is installed at which point it won't even be possible to check.

     
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  3. oldbutnotdead

    oldbutnotdead

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    Is this for a suspended timber structure? If yes then hook the rubbish out, 150mm is a minimum, quickly gets eaten by pipe runs and similar.
    That spare concrete should come out with a pickaxe and a hammer- it's not been tamped, it's not in a trench, just lever it up with the pickaxe or a mattock, hit it with a sledgehammer or lump hammer & it'll be gone.
    Next time look at volumetric mixers- only pay for what you use, much easier life :)
     
  4. TheDeuce

    TheDeuce

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    Thanks - it's not for a suspended timber structure, the foundation beams as opposed to slab are due to it requiring piling - made ground...

    If it were timber, hell yes I'd care about the ventilation. It's not though, so I personally am pretty happy to just accept that in some places it's not quite 150mm but that the beam and black floor will be just fine anyway.

    However, it's not about what I'm happy with - it's about what building control consider reasonable. Should I be concerned about it failing on a technicality? And does the 150mm requirement include ground already effectively beneath concrete, which is itself a very durable barrier.
     
  5. ^woody^

    ^woody^

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    And oversite concrete should be smoothed with the back of shovel or suchlike, not left rough or uneven.
     
  6. Bouy

    Bouy

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    As per cl x.y.z of Document ? of the Building Regs :)
     
  7. Tigercubrider

    Tigercubrider

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    why would you worry about the cost?
    a "builder" cocked up.
    It's his problem at his expense.
    It will be softer now than in a week/month while you talk about it.
     
  8. ^woody^

    ^woody^

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    As per if the OP is paying for work to be done to a correct BS/EN standard with no problems later.
     
  9. TheDeuce

    TheDeuce

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    I paid the groundworks guy to do the piling, including arranging the delivery and pouring of the concrete to form the beams. I was a bit disappointed at the relatively scruffy disposal of the excess concrete but hadn't realised until after making final payment that it was in places slightly too high to provide a minimum 150mm void in those areas.

    The question remains whether or not that's actually an issue. Is it one of those things that isn't ideal, but generally the void exists and is about right, so forget about it? Or is it something that is critical or at least policed as such?
     
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  11. TheDeuce

    TheDeuce

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    It's deeper than it looks... The soil on the outside of the ply shuttering was dry so the sides has slumped during excavating. The guy pouring the concrete saw the resulting deep wedge shape gap as the ideal place to lose the last half tonne or so of concrete! I would guess the bit you think looks shallow, is actually around 400mm deep on average.

    It is just concrete still, and not reinforced so it will break, but I'll need a powered breaker I think. I haven't actually tried a pickaxe/mattock yet - if you really think it'll be enough I'll gladly buy one for a few quid and get it done..
     
  12. oldbutnotdead

    oldbutnotdead

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    I don't know why 150 void is required for your setup, be worth a quick call to your BCO and see what they have to say,- 400mm would need a bit of drilling for sure
     
  13. TheDeuce

    TheDeuce

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    The 150mm void is the minimum requirement: https://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2011/Part5/section2/default.htm

    Although as I say, I have no idea how well respected or policed it actually is! The only reason I haven't asked the BCO yet is that part of me is wondering if will ever care to or get an opportunity to check. His last visit was before the foundation beams were poured, and he said his next visit will be after the beam & block floor is in... But given part of fitting the floor is to final grout the blocks, at that stage how can he get under there with a tape measure anyway..

    I'm really not trying to 'get away' with anything here. I simply don't have the building experience to know when something is considered acceptable or when it won't be. Or in this case, if anyone other than myself would even give it a second thought.
     
  14. Bouy

    Bouy

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    Pick axe and sledge hammer should break it up if it wasn't compacted down, the sooner the better. All depends if your BCO goes by the book, at the end of the day air outlet pipes only have to be 100 dia so you would think 100 deep at the edges shouldn't be that big an issue and even more so since its block and beam. Over to the BCO.
     
  15. TheDeuce

    TheDeuce

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    This is my view - it should be fine and I have certainly made sure there is sufficient vents around the new extension and connected air passages through to the existing house floor void, all by the book and I really can't see how a few high spots of concrete will effect the overall requirement to ventilate.

    But... As it it's only a relatively small area, I think I will smash away as much as I can without being too anal. Luckily most of it is just within the limit anyway. Two hours of back breaking work should sort it ;)
     
  16. ^woody^

    ^woody^

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    If 150 is the requirement, the only one who will decide if any less will be acceptable is your building inspector.
     
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  17. denso13

    denso13

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    All I would say is, do it properly, most people only do it once. If the inspector is happy for less he may have had a bad day. Just do it properly and it won't niggle away at you in the future.
     
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