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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • 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:
  1.  
    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).
  2.  
    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.
  3.  
    What budget tape does one recommend?

    Thanks
  4.  
    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.''
  5.  
    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
    • CommentTime7 days ago 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
    • CommentTime7 days ago
     
    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
    • CommentTime6 days ago
     
    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
    • CommentTime6 days ago
     
    It's good to have it confirmed that there's a reason to pay for the specific airtightness tapes.
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