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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthortony
    • CommentTimeFeb 4th 2013
     
    We all think that you read this thread carefully before you spend on foil

    http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=27#Item_30
  1.  
    And for a summary of the facts - page 74 here http://www.rcimag.co.uk/rci-oct-2012/#/74/
  2.  
    So Mike , quick answer , multifoil works fine (does what it claims), yes or no :)
  3.  
    Never a straight answer for that one.

    If you are asking about products tested via hot plate - then Yes, predictions are as reliable as any other insulation tested via the same method.

    If you are talking about products which rely on comparative testing...I don't want to get sued...
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 4th 2013
     
    Could you explain in detail and with example the last sentence on page 74 please :wink:
    • CommentAuthorMike George
    • CommentTimeFeb 4th 2013 edited
     
    You mean 'Complementing its airtightness is a Certified Vapour Resistance of 6000MNs/g thus rating as an effective Vapour Control Layer'?

    The Mu factor of the multifoil can be calculated from the Laboratory tested Vapour Resistance 6000 (MNs/g) x 0.2 (vapour permeability of still air) / 0.033 (m)(thickness of foil)

    = Mu factor 63,634

    To put this into context Mu (Rubber) = 10,000 Mu (Polythene) = 100,000

    So Mu (Multifoil) 63,634 is a pretty useful Vapour Control Layer.

    I should say however that Mu factors for foils vary dramatically. Some manufacturers offer more than one product at opposite ends of the scale as some applications require low Mu factors.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 4th 2013
     
    :cool:
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013 edited
     
    Any MF that is held together by quilt stitching has zero resistance to either air or vapour. Don't know if any of the manufs still use quilting, but they certainly did at the time of the infamous twin shacks test. So the 'explanation' given by detractor/sceptics for the decent performance of the MF shack - that it must have been due to better airtightness - were rubbish.
  4.  
    Hi Tom,

    As I mentioned above, there are (nowadays) many multifoils with many different properties.

    I don't know the history of what was used when and where.

    In terms of comparative vapour and air resistances, are you suggesting that mineral wool and the 'quilted multifoil' used in the shack tests had exactly the same values for vapour and air tightness? because if they did not then this will have clearly affected the results would it not?
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013 edited
     
    Posted By: Mike GeorgeIn terms of comparative vapour and air resistances, are you suggesting that mineral wool and the 'quilted multifoil' used in the shack tests had exactly the same values for vapour and air tightness?
    Near enough - as in averagely gappy and/or holey, as was the norm back then. I did a little calc, that the total area of the lots of little holes for quilting (measured from a sample) was equiv to one 80mm diam hole per m2! Might even have been worse than the min wool shack.

    Posted By: Mike GeorgeI don't know the history of what was used when and where.
    The Actis 9 product of that time, which the test referred to, was definitely stitch/quilted - they briefly offered a spot welded alternative called something else but withdrew it.
    • CommentAuthorBeau
    • CommentTimeFeb 5th 2013
     
    Tom

    I still have an off cut of some Triiso super 9. Now I cant test with air but I could make a little test to see how quickly water permeates through it. I realise water and air do behave in the same way but do you think the test would be of any interest?
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013
     
    No - water and air not comparable - surface tension might ensure no water at all drips thro. Instead, put it to your mouth and suck! or just look at all the stitch holes.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2013
     
    Why can't you check with air.

    Get a hair dry (on cold) and a microphone on your PC push different materials against the nozzle (or make a bag from them would be better as it has a larger surface area), record the noise the hair dryer makes and then analyse that noise with some free software to see what the pitch is. Would work for a comparison.
    • CommentAuthorBeau
    • CommentTimeFeb 5th 2013
     
    Air can get through the stitching. I fixed some multifoil over the end of an industrial vacuum set to blow. I could not feel the air going through so I put some very fine dust over the stitching which was blown out in places but not on all stitch holes. ST if you can devise a more mechanically based test I am happy to have another go but mics and computers are not my thing :bigsmile:
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013 edited
     
    Just
    Posted By: fostertomput it to your mouth and suck!
    - as gently as you like! The result leaves no doubt.
    • CommentAuthorMike George
    • CommentTimeFeb 5th 2013 edited
     
    Does anyone have a pdf copy or a link to the original TRADA Cerificate for the Actis product? Not sure if it has ever been linked to here but not keen on re-reading 800+ posts

    There may be some listed properties which may help
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013
     
    Posted By: Mike Georgesome listed properties which may help
    Grade 1 or 2*?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2013
     
    Posted By: BeauST if you can devise a more mechanically based test I am happy to have another go but mics and computers are not my thing
    Do the same and use a set of tuning forks, or a piano :wink:

    What is brown and sounds like a bell?

    (you ready for this)

    DUNG
  5.  
    It was always a cracked bell in my day. It went as a set with 'What's brown and steaming and comes out of cows?' The Isle of Wight ferry..... (Works better spoken!)
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2013
     
    :bigsmile:
    • CommentAuthorBeau
    • CommentTimeFeb 5th 2013
     
    <blockquote><cite>Posted By: fostertom</cite>Just<blockquote><cite>Posted By: fostertom</cite>put it to your mouth and suck!</blockquote>- as gently as you like! The result leaves no doubt.</blockquote>

    Done that now Tom very tasty I might add. It is safe to say air can pass through the stitching relatively easily. This surprised me as I have been very pleased with it and the wisdom I picked up from this forum is because it is a good airtight membrane.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2013 edited
     
    Consider the pressure of wind, or even internal air buoyancy on a calm day - it's enormous! Enough to shift a yacht or an air balloon. Enough to need sometimes incredible structural wind bracing. Such forces squirt air thro the tiniest gap, but building people seem to think 'it's only a small crack' or that a scrap of sellotape will seal it. Tell that to any other trade that has to manage fluids - sailors, plumbers ...
    • CommentAuthorBeau
    • CommentTimeFeb 5th 2013 edited
     
    I am not doubting you Tom but if it is not a good airtight membrane and it works well (which in my view it does) then it must somehow be a good insulator in it's own right.
  6.  
    Except that multi foil tends to be installed behind plasterboard that is taped and skimmed, considerably adding to overall air tighness. Apart from sockets and switches, there wont be air blowing directly up against the MF.

    And even if it is very leaky, its a hell of a lot more airtight then what was there before, ie gale blowing through an open attic/roof space. It has been argued that it is this difference that accounts for the large difference felt after MF has been installed.
  7.  
    We used TLX Gold, which is a multifoil combined with a membrane and installed this over our rafters. It performs the same job as roofing felt, but also provides an element of insultion and air tightness without raising the height of the roof. We left a 25mm air gap beneath the foil and then installed kingspan between and below the rafters.
    •  
      CommentAuthorMartian
    • CommentTimeMay 1st 2013
     
    Well well well, still scrapping away I see ...
    Just thought I would check in to say I'm still alive and kicking. :bigsmile:
    Best wishes to all.
  8.  
    Well hello Martian! Welcome back! (or have you always been there, in the background?). I used multifoil for the first time earlier this year. Not a 'choice', but a necessity in the circs. Still a sceptic.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 2nd 2013
     
    Hi Martian
    •  
      CommentAuthorMartian
    • CommentTimeMay 2nd 2013
     
    I have been rather busy and only reading stuff occasionally but also stayed away from the mulitifoil debate on purpose as it was getting like "Groundhog Day". A new Building Regs application came in a few days ago though and specified "Tri-Iso 10+" and still with some extravagant and unsubstantiated U-Value claim. In the process of checking it out I had a skim over the last couple of years on this thread.
    Plus ça change, plus c'est la même chose ....
  9.  
    In trying to help a client trouble-shoot re very poor insulation and air-tightness detailing to his new attic conversion I had cause to converse quite a bit with Actis' tech dept, and found no extravagant claims, and a recognition that the usual lay-up on sloping soffits would include Tri-iso 10 *and* Pu/PIR to achieve a compliant U value of 0.18W/m2K. As a cynic still re multifoil, I found the tech dept very forthcoming.
   
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