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Is a separate VCL necessary below screed when using foil faced PIR?

Discussion in 'Building' started by ChrisZx, 16 Jul 2019.

  1. ChrisZx

    ChrisZx

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    As per the title really, not sure if taping the joints between boards is sufficient or whether a separate VCL is required?

    Seems a bit pointless when the clips for the UFH pipes will penetrate through it into the PIR anyway...
     
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  3. ^woody^

    ^woody^

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    It's not a VCL and taping the joints is not required as the joints should be tight anyway, but is good practice.
     
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  4. ChrisZx

    ChrisZx

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    Thanks, but does that mean:

    A VCL is not required and the foil facing is ok

    or:

    A VCL is required and the foil isn't good enough?
     
  5. ^woody^

    ^woody^

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    A VCL (or foil face used as a VCL) is used in a timber structure (wall, floor ceiling, roof) to stop water vapour getting through to the timber. So its not a requirement in a concrete floor.

    If you were pouring wet concrete, then a polythene layer (or taped joint) may be useful to stop water dripping through joints and lifting the insulation. But as you will be using dry screed, such precautions are not required for this.
     
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  6. Notch7

    Notch7

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    Recently a builder told me that a building inspector had said they have found cementitious screed eats PIR and so a polythene separating layer is needed.

    Ive also heard that some building inspectors like to see a plastic sheet between insulation and screed to act as a 'slip layer' with underfloor heating.

    I cant say Ive heard any official confirmation so feel free to ignore!

    Dont forget to use perimeter expansion foam between screed and walls......
     
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  7. ^woody^

    ^woody^

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    The only eating going on there would be of magic mushrooms.

    The "slip layer" you mentioned is for the reason I mentioned above regarding water.
     
  8. wessex101

    wessex101

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