Warm roof sealing

Discussion in 'Roofing and Guttering' started by essex123456, 14 Jul 2021.

  1. essex123456

    essex123456

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    We are in the middle of a rear extension, this has a warm roof. where the joists run over the external wall there was a gap between the insulation and the wall. i.e letting in cold air from the soffit, this would have been below the warm roof and above the plasterboard ceiling. I also had the same on the house side where the new build meets the old house and a cold roof. I have now sealed these gaps with celotex? basically I have sealed the new warm roof from cold ingress under it, is that correct? and also do I need to add a VCL to these parts as on the underside of the warm roof?

    Thanks for the help
     
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  3. noseall

    noseall

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    Yes spot on. The reality is that there should be a continuation of insulation from the warm deck inso' down to the cavity jnso'.
    Most of us do the entire with Celotex. etc
     
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  4. essex123456

    essex123456

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    Thanks for the reply. do I need to put a VCL over these bits?
     
  5. noseall

    noseall

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    Vcl needs to be under the (ceiling) plaster board.
     
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  6. Buildme

    Buildme

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    Has the VCL not supposed to be under the insulation on a warm roof on top of the osb. This is my understanding.
     
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  8. noseall

    noseall

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    Yes. You need to prevent internally produced moisture getting beyond the insulation layer.
     
  9. Buildme

    Buildme

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    But you have it under the plasterboard? Or do you mean both? Would this not create a place for vapor to get trapped if it went through the barrier under the plasterboard and can't get out through the roof because of the VB on the roof.
     
  10. noseall

    noseall

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    Warm roof it can go as close to the warm side of the insulation as you dare. We would fit duplex boards also.
     
  11. Buildme

    Buildme

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    Duplex board? Is this the foiled back plasterboard?

    Not that I'm doubting you but would this not trap moisture between the board and vapor barrier if anywhere to get through the boards with the VB on top of the osb on the roof.
     
  12. noseall

    noseall

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    Moist air exists below the VCL whether you like it or not. Stopping at any point is good.
     
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