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Housing - Renovation: Celotex - taped joints as VCL?

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  1.  
    • CommentAuthorsmudger
    • CommentTimeJul 8th 2016
     
    I have just realised that celotex claim that a separate VCL isn't required if joints are taped. Is this reliable and detail / products to make sure it works? or would you still install a seperate layer?
    • CommentAuthorDarylP
    • CommentTimeJul 8th 2016
     
    On Cx, the alu foil facing on the PIR is practically vapour impermeable, and IF all the joints are taped properly with alu-foil tape , you will be fine.
    Just make sure the Cx is clean/dry/dust-free before you tape it! :wink:
    • CommentAuthortony
    • CommentTimeJul 8th 2016 edited
     
    Yes but for how long and what about joining to other vapour barriers in other elements
    • CommentAuthorDarylP
    • CommentTimeJul 8th 2016
     
    the 'proper' alu-foil tape will last for at least 4 years exposed to the wind/rain/sun, as long as the substrate is clean/dry when the tape is applied.
    Join it with Tescon/similar to other membranes/layers ?
    :smile:
  5.  
    I try not to use the foil tape, as the quality of the adhesive seems to vary from roll to roll. Also, when using it at right angles (say from a ceiling and down onto a wall) there is a tendency to split the tape with your thumb-nail as you smooth it out. I mainly use Tescon or Uni-tape. Very occasionally (I have had it happen with Recticel PIR board) the foil seems to have a 'waxy' coating on it, which resists almost any tape.
    • CommentAuthorsmudger
    • CommentTimeJul 8th 2016
     
    Thank you
    • CommentAuthorsmudger
    • CommentTimeJul 8th 2016
     
    I confess I hadn't looked 'beyond' Celotex - any reason to use Recticel? Compression is lightly better (140v120) and vapour resistance is lightly lower (100v150).
  8.  
    Recticel is cheaper! C-----x and K------n tend to be top of the price range and other names a bit cheaper. If you want the 'top names' it is worth a barter, though. I got a price for Recticel from my merchant and then, despite it having the relevant BBA certs, my BCO wanted K------n. I told the merchant this and they supplied the latter for the same price as Recticel.
  9.  
    What budget tape does one recommend?

    Thanks
  10.  
    This one doesn't. As above: ''I try not to use the foil tape, as the quality of the adhesive seems to vary from roll to roll. Also, when using it at right angles (say from a ceiling and down onto a wall) there is a tendency to split the tape with your thumb-nail as you smooth it out. I mainly use Tescon or Uni-tape. Very occasionally (I have had it happen with Recticel PIR board) the foil seems to have a 'waxy' coating on it, which resists almost any tape.''
  11.  
    Do you seal PIR between rafter to the rafter? Or just the PIR below?

    I only need one roll, is it readily available to pick up from screwfix or similar can't find much?
    • CommentAuthorkayserasera
    • CommentTimeDec 5th 2017 edited
     
    Posted By: VictorianecoDo you seal PIR between rafter to the rafter? Or just the PIR below?


    Good question. These are the sorts of details I'm looking for
    • CommentAuthortony
    • CommentTimeDec 5th 2017
     
    It needs to be sealed or tightly fitted to the rafters ro stop thermal bypass

    The vb/air tightness barrier needs to be all joined up to itself and adjacent elements hermetically.
    • CommentAuthorjonc_uk
    • CommentTimeDec 7th 2017
     
    I think you will find the foil tape will not stick to wood.

    My experience of it is that even if it is smoothed/rollered it will still un-stick itself over time. I have a warm roof with two layers of PIR both taped and on a frosty morning I can see areas where there is obviously air leaks. Its an outbuilding put up a few years ago and has no VCL except the foil backing of the plasterboard.

    After insulating the loft of my house with PIR between and under the rafters I now recon I could have improved things with a VCL between the two layers, even though it would have screws through it. It is mostly foamed using low-expansion foam-fix after I realised the tape was not working.
    •  
      CommentAuthordjh
    • CommentTimeDec 7th 2017
     
    It's good to have it confirmed that there's a reason to pay for the specific airtightness tapes.
    • CommentAuthorkayserasera
    • CommentTimeDec 21st 2017 edited
     
    Posted By: jonc_ukI think you will find the foil tape will not stick to wood.

    My experience of it is that even if it is smoothed/rollered it will still un-stick itself over time. I have a warm roof with two layers of PIR both taped and on a frosty morning I can see areas where there is obviously air leaks. Its an outbuilding put up a few years ago and has no VCL except the foil backing of the plasterboard.

    After insulating the loft of my house with PIR between and under the rafters I now recon I could have improved things with a VCL between the two layers, even though it would have screws through it. It is mostly foamed using low-expansion foam-fix after I realised the tape was not working.


    Is it worth taping PIR foils together if you are having a separate VCL sheet? A waste of time? Only for pedants?
    • CommentAuthortony
    • CommentTimeDec 21st 2017
     
    nope and pedants will realise tape has limited life :)
  18.  
    Thanks. Is there a special technique to seal sheets of polythene without tape?
    • CommentAuthortony
    • CommentTimeDec 21st 2017
     
    Yes, it is called a welted joint. Both sheets are lifted perpendicular to the face of wall, floor or ceiling, folded over several times til down to the surface, can be trapped on a joist, batten or rafter and fixed through.

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