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Bridging cavity gap for floor insulation

Discussion in 'Building' started by mordzy, 20 Jun 2019.

  1. mordzy

    mordzy

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    Hello. I’ve recently been laying celotex 150mm myself in my extension ready for the UFH and screed.

    When coming to the folding doors I’m not exactly sure what to do to bridge the cavity.

    I’ve read a couple of threads on here about filling with concrete but I’m not sure if this is right. I’d also contemplated standing up some celotex on its end. Any advice would be appreciated.

    I’ll try upload or host a pic somehow
     

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  3. Notch7

    Notch7

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    Is it a 100mm cavity?

    With 150mm celetex, I wonder if you need to do anything tbh.

    I suppose you could screw a few steel brackets for the indulstion to sit on.

    I know the cavity can be filled up, but keeping a cavity stops any chance of leaks through the cill getting inside
     
  4. Bonni

    Bonni

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    The inner leaf blocks/bricks should have been omitted. Remove them.

    Upstand dpc against face of bricks below doors and have 25mm upstand of celotex. Then continue 150mm through to upstand celotex.

    Also, I avoid fitting doors to the outer leaf. I step the outer brickwork in and fit the doors in the cavity. You don't have any dpc on the reveals, there's a chance it will rain in. the dpc should cover the face of the bricks on the outer leaf of the reveal and tuck into the cavity. Then seal the doors to the dpc and trim off.

    Position of doors, bricks below doors and blocks on the inner leaf are not the best way to have done it. Who's your builder!
     
  5. mordzy

    mordzy

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    Ok so I should chisel the inner block work to be level with the slab under the celotex. Tuck the existing pc material between the slab and celotex, stand celotex up in the cavity and run the top layer of celotex over it up to the outer wall?

    I’ve had this debate with the architect and builder. I’m not in the trade so been lead by both in this situation.
     
  6. Notch7

    Notch7

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    Oops, sorry I didnt look at the pics.

    Yes blockwork should be flush with the concrete slab.

    Brickies always want to run the blockwork all the wsy round at dpc level -even when they promise not to :ROFLMAO:

    If you do as above, ie put a bit of 25mm celetex vertically then fit the floor celetex across the cavity -I doubt it needs any support as the screed will be strong enough to cantilever over 75mm
     
  7. mordzy

    mordzy

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    Ok thanks both for that. Will I get a clean ish line chiselling the block work out or I there a better way?

    For ref, the floor insulation is 100mm celotex with a further 50mm celotex on top. If I chisel blocks down to slab level and upstand some in cavity the same height as the 100mm, I should be able to run a board of 50mm over top and.

    My main concern was about ‘filling’ the cavity as sounds counter intuitive
     
  8. noseall

    noseall

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    Not when you think that some builders actually build the door openings into the internal leaf blockwork from the foundation or above floor level upwards.

    We always try and plan for a single engineering brick to finish the internal walls up to DPC. This means you can knock off that brick when it comes time to screed the floor.
     
    Last edited: 21 Jun 2019
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  10. mordzy

    mordzy

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    I think the internal block that sits higher than the slab it’s a full block, so knocking the entire block out would mean the block works is lower than the slab. Is this ok? I thought best to chisel the block in half so it’s flush with the slab?
     
  11. noseall

    noseall

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    Yes. It serves no purpose.
     
  12. mordzy

    mordzy

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    Brill thanks, I’ll get that done and update with pics
     
  13. Notch7

    Notch7

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    Thats a good idea.

    If you run the insulation and screed over the cavity, do you put in a support for the insulation or just assume the screed will have enough strength over that small distance.

    The other thing I notice is the dpm doesnt want to push out to the reveal corners.
     
  14. mordzy

    mordzy

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    Just coming back to this. Im worried about knocking out the inner leave as it appears to support the folding doors via metal brackets (see pic).

    Ive held of doing anything yet as with the recent rain the DPC membrane filled up with about a washing up bowls worth of water. I checked with the hosepipe and noted the silicone has failed at the bottom of the door but also, and weirdly the water tracks in via the cement Line under the lintel and fills the DPC membrane. Builders been back and suggested grinding it out and re pointing but he couldn't understand it. Also window company coming back to re silicone.

    So with regards the cavity bridge, I might have to hold off till my hosepipe test passes, but I'm wondering if it would be better based on what I have to put some sort of metal cavity closer in, thus retaining the window bracket fixings and just run the screed over?
     
  15. mordzy

    mordzy

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    anyone?
     
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