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Housing - Renovation: Is there a quicker/better way of doing the VCL?

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    See main wall in attached photo

    Wall envelope as follows, layer by layer:

    - retaining (damp) stone wall
    - oldroyd cavity membrane
    - metal studwork
    - 25mm PIR
    - 25mm timber battens, with 25mm PIR in-between

    No space for wall to be any thicker due to location of external doorway

    I realise it would have been cheaper and easier to put in a dpm across the whole wall, but something about puncturing a flappy dpm (which will surely happen not least by the plasterboard screws) along with the dpm not being bonded to the PIR throughout (like the foil layer is) put me off... Is this illogical thinking?

    Perhaps I should have used less insulation and put in a dpm followed by osb for protection then the plasterboard...

    What would others have done?
      IMG-20211002-WA0003.jpg
      IMG-20211002-WA0004.jpg
  2.  
    You could still put on a DPM as VCL if you are concerned about the integrity of the foil and tape as a VCL. Just make marks on the adjoining walls as a guide to your batten spacing, fix the DPM with double-sided tape. Then 'ping' a chalk line and proceed to fix the plasterboards.

    If you are happy that the foil has no 'dings' and the taping is well tight, go with in as it is - plasterboard straight on top of the PIR.

    If concerned by the 'piercings' what about measuring off where the screws will go, and put a small square of double-sided butyl tape where each screw will go? That will go some way towards sealing the screw-holes.
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2021
     
    Posted By: ChrisinYorkshireI realise it would have been cheaper and easier to put in a dpm across the whole wall, but something about puncturing a flappy dpm (which will surely happen not least by the plasterboard screws) along with the dpm not being bonded to the PIR throughout (like the foil layer is) put me off... Is this illogical thinking?

    One alternative that was there but not really proved when I built around 2014 is a paint-on vapour barrier. I think they're proven now.

    As far as plasterboard screws, most vapour membranes are designed to seal around minor penetrations I believe, but you could coat the screws with some glue or somesuch if you were very keen. I put patches of butyl rubber behind where I had drilled holes for coach screws to seal the gaps there, for example.
  4.  
    Thanks Nick, I've put the plasterboard up now, (well nearly finished), having obsessively checked every square mm of the foil with a torch. The question was in relation to future projects, (always learning)... I like the idea of the butyl but fear the hours involved :cry:
  5.  
    Posted By: djh
    Posted By: ChrisinYorkshireI realise it would have been cheaper and easier to put in a dpm across the whole wall, but something about puncturing a flappy dpm (which will surely happen not least by the plasterboard screws) along with the dpm not being bonded to the PIR throughout (like the foil layer is) put me off... Is this illogical thinking?

    One alternative that was there but not really proved when I built around 2014 is a paint-on vapour barrier. I think they're proven now.

    As far as plasterboard screws, most vapour membranes are designed to seal around minor penetrations I believe, but you could coat the screws with some glue or somesuch if you were very keen. I put patches of butyl rubber behind where I had drilled holes for coach screws to seal the gaps there, for example.


    I've sometimes wondered (hoped), whether the tescon tapes self seal to some degree, around screw penetrations. Not tried paint on VCLs...
  6.  
    My gut feeling is that the cloth tapes will be to some extent 'self-sealing', but the paper tape less so.
    • CommentAuthortony
    • CommentTimeOct 3rd 2021 edited
     
    Single sheet of thin poly for me over the whole lot, lapped and welted to ceiling membrane
    •  
      CommentAuthordjh
    • CommentTimeOct 3rd 2021
     
    Posted By: Nick ParsonsMy gut feeling is that the cloth tapes will be to some extent 'self-sealing', but the paper tape less so.

    Yes, I believe that's the case.

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