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    • CommentAuthorTimber
    • CommentTimeJan 25th 2009 edited
     
    ...
  1.  
    Well, I can add that I have a full loft extension covered with the stuff and can say it works pretty damned well (Warm roof type construciton). I can't claim its better than 200mm or whatever of celotex, but I do know that its a large space, with lots of external surface area and needs very little heating. I'm a chartered chemical engineer and have a degree in this kind of stuff (heat transfer etc), so I reckon multifoils work pretty well.

    Its also the consensus at work, amongst the other engineers & architects I work with.

    Tim
  2.  
    Hi Tim,

    What you say is interesting. When you say warm roof, do you mean that the mf is sandwiched between the rafters and the tiles?
    Care to give more details of the type of building, heating system and how the mf was installed?
    • CommentAuthorbiffvernon
    • CommentTimeJan 26th 2009
     
    Posted By: dimengineerI'm a chartered chemical engineer and have a degree in this kind of stuff (heat transfer etc), so I reckon multifoils work pretty well.
    Excellent. You'll be able to tell us what and how the internal foils do then, including comments on cost effectiveness of those internal layers, as would be expected of a professional engineer.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 26th 2009
     
    dimengineer, Don't mind Biff - he's already been told what the internal layers do but doesn't want to acknowledge. I'd be very interested in your take on it. Here's my most recent effort, from http://www.aecb.net/forum/index.php?topic=1649.0
    ------------------------------------------
    AFAIK, the main point is that the ratio of conductive to convective to radiant modes of heat transfer at micro scale across the void spaces within any insulation, differ markedly, depending on whether the micro scale temp gradient across a void space (and it surrounding solid matrix) is steady-state, or dynamically varying.

    In steady-state conditions, conduction and convection greatly outweigh radiant transfer across the void. In dynamically varying conditions, radiant transfer dominates over conductive and convective.

    Some thought and visualisation will reveal why - it's to do with the instantaneous nature of radiant transfer versus the time-lag nature of conductive and convective.

    That difference doesn't matter under long-established steady-state temp gradient conditions, when 'beginning' and 'end' of the transfer are long gone/still to come.

    However under constantly varying temp gradient conditions, when every moment is a new 'beginning', all modes - conduction, convection and radiation - start instantly. But of the three, only radiant gets received instantly; conduction and convection get received after a time-lag. As a result, radiant gets the new variant portion of the temp gradient filled-in long before conduction and convection get there. So conduction and convection are always beginning, but soon petering out as the temp gradient disappears; the temp gradient disappears because it's infilled by the radiant, with little 'help' from the conduction and convection.

    So, under steady-state temp conditions e.g. as laboriously and unnaturally established in the hot-box, conductive and convective modes of transfer prevail, across the voids within an insulant. Conventional insulations are good at resisting that; multifoils are as poor at that as you'd expect.

    Under real-life dynamically-varying temp conditions, the radiant mode of transfer prevails, across the voids within an insulant. Conventional insulations offer little defence against that; their internal surfaces, being average mud-colour, have average reflectivity. Whereas an insulant that majors on resisting radiant transfer, such as multifoils, will do splendidly under such conditions.

    It's not that multifoils perform as well, under real-life dynamically-varying conditions, as other insulations are expected to. It's that conventional insulations in real-life fail to fulfil the expectations of their steady-state hot-box tested k-value ratings, by a factor of 1:1.5 to 1:2, or worse. Whereas multifoils do much better.

    Well, that's my version - I'd appreciate comment.
    • CommentAuthorTimber
    • CommentTimeJan 26th 2009 edited
     
    ..
    •  
      CommentAuthorfostertom
    • CommentTimeJan 26th 2009
     
    So also with most multifoils, which are peppered with stitch holes - on a recent rough calc giving open-area equiv to a 81mm sq hole per m2. Some multifoils are imperforate, being spot-welded through - or else connected only along the edge, which may be cut off once cross-battened into place.
    • CommentAuthorTimber
    • CommentTimeJan 26th 2009 edited
     
    ..
  3.  
    Posted By: dimengineer I'm a chartered chemical engineer and have a degree in this kind of stuff (heat transfer etc), so I reckon multifoils work pretty well.

    Its also the consensus at work, amongst the other engineers & architects I work with.

    Tim


    I wouldn't touch them with a barge pole. The UK authorities did pull the plug on multifoil radiant barriers, when used on their own.

    I note that a US Court fined a multifoil supplier over $100,000 for making misleadingclaims about his product. Full story at:


    The British Advertising Standards Authority got Actis, a French company, claiming their reflective foil insulation is 'Equivalent to 200mm of traditional Rockwoool insulation'. A complaint has been upheld after ASA went to independent technical experts.

    The judgment can be seen at:

    Think hard before you buy.

    The ruling:

    Actis Insulation Ltd
    Unit 1
    Cornbrash Park
    Bumpers Farm Industrial Estate
    Chippenham
    Wiltshire
    SN14 6RA

    Date: 31st May 2006
    Media: Brochure

    Sector: Household

    Public Complaint From: Gloucestershire

    Complaint:

    Objection to a brochure for roof insulation. The brochure stated "TRI-ISO
    SUPER 9 Insulation for roofs ... Thermally equivalent to 200 mm of mineral
    wool when installed in a roof situation, as certified by the European
    certifying body, BM TRADA CERTIFICATION (following real building trials,
    certification n°0101) ... THERMAL EFFICIENCY equivalent to 200 mm of
    mineral wood RT = 5* ... *in situ measured values." The complainant
    challenged:

    1. the claim "Thermally equivalent to 200 mm of mineral wool" and

    2. the quoted thermal resistance "RT = 5".

    Codes Section: 3.1, 7.1 (Ed 11)

    Adjudication:

    Actis Insulation Ltd (Actis) said they had stopped advertising TRI-ISO
    SUPER 9 because it had been replaced with their new product TRI-ISO SUPER
    10. They said the efficiency of their products was demonstrated by their
    track record in the market. Actis said they had commissioned BM TRADA
    Certification Ltd (BM TRADA) to test, assess and report on the TRI-ISO
    Super 9 product. They provided us with a copy of the BM TRADA
    Certification and Report dated August 1997 and said that it substantiated
    their claims. Actis explained that TRI-ISO Super 9 was different from
    traditional bulk insulation because it was a multi-foil product that used
    layers of reflective foils spaced with synthetic wadding and foams. They
    said the product required less space than traditional bulk insulation and,
    therefore, internal insulation cavities could be made smaller and internal
    useable spaces could be enlarged without compromising efficiency of
    insulation. Actis argued that traditional methods of testing were not
    appropriate for their product because traditional methods measured thermal
    efficiency mainly by conduction and did not take into account the
    influences of convection, radiation and change of phase. They said their
    product combined various energy transfers of radiation, conduction,
    convection and change of state rather than just conduction. Actis also
    argued that traditional methods of testing did not allow representation of
    the real behaviour of building materials once used on site. They pointed
    out that BM TRADA had used "in situ" testing involving a real external
    environment with variations in temperature, humidity, etc. rather than the
    traditional methods of laboratory testing. Actis maintained that the BM
    TRADA Certification demonstrated the thermal efficiency of their product
    and provided proof of their claims.

    1. Complaint upheld

    The ASA obtained expert advice. We understood that BM TRADA had tested
    TRI-ISO SUPER 9 and the mineral wool in two separate roof installations.
    However, we noted that BM TRADA had not used the standard industry methods
    of testing and that the report provided by Actis did not include
    sufficient detail to support their own methods of testing.

    We acknowledged that BM TRADA Certification was a leading multi-sector
    certification body accredited by the United Kingdom Accreditation Service.
    We considered that the BM TRADA report did not provide enough detail to
    support their methodology instead of the methodology employed by the
    internationally recognised ISO industry standards. We concluded Actis had
    not substantiated the claim. We noted the ad was no longer appearing but
    told Actis not to repeat the claim in future advertising until they were
    able to provide sufficient substantiation.

    2. Complaint upheld
    We understood that RT was a symbol of total thermal resistance and
    typically had the standard unit of measurement of m²K/W. We noted that the
    claim "RT=5" was not qualified by any recognised units of measurement e.g.
    m²K/W and a small footnote stated only "in situ measured values" without
    further explanation. Because the value of 5 was not qualified by any
    recognised units of measurement, we considered the claim "RT=5" was
    ambiguous and should be qualified in future. However, we noted that the BM
    TRADA report did specify an overall resistance (RT) of 5.0m²K/W derived
    from the in situ testing. We understood that the in situ measured values
    did not meet with ISO recognised international standards for determining
    declared and design thermal values for building materials and products.

    We considered that the BM TRADA report did not include sufficient detail
    to demonstrate the validity or robustness of their testing methodology
    instead of the methodology employed by ISO standards. We concluded that
    the report did not substantiate the claim " RT=5". We told Actis to remove
    the claim until they were able to provide sufficient substantiation.

    The brochure breached CAP Code clauses 3.1 (Substantiation) and 7.1
    (Truthfulness).

    Further to the above:

    The UK authorities pull the plug on multifoils, when used on their own. The Multifoil Council) made pleaded to the Office of the Deputy Prime Minister when the last round of Part L (energy aspect) of the building regs was being assessed and had a reprieve to 01/01/2007 to give them time to show that multifoils worked as claimed. This reprieve has been rescinded early because of convincing evidence that the multifoil claims are exaggerated. Multifoils will only be permissible if they can pass hot box tests, which as far as I know they have never have. All the local authorities and the NHBC and such bodies have all been told to no longer accept multifoils. I am not sure if this is still the case.
  4.  
    Its not the case. It is up to the individual officer to decide whether or not to accept the manufacturers claims. This siince a legal ruling last year which threw out the need for multifioil to be tested in accordance with BR443, Ie. via hot plate test. This is discussed several pages back on this thread.

    Also, at least two multifoil manufacturers have BBA Certificates for their products, allbeit with supplementary insulation. This also discussed a few pages back.
  5.  
    Posted By: Mike George...several pages back...


    What a thread!
    • CommentAuthorskywalker
    • CommentTimeJan 26th 2009
     
    Timber

    We've talked about real actual U values of stuff such as mineral wool in an a gale elsewhere in shorter threads (OK MUCH shorter threads). Consensus is that 'we know the short comings of the hotbox method - but we are stuck with it' (terrible paraphrase but more of less it) and basically fleece in a wind is clearly not going to perform up to its stated values.

    Now James this Granny thing. I have several available but all are different thicknesses and it is proving hard to get them to form into an even sheet - any clues.

    Can you be imperforated?

    I'll get my coat.

    S.
    • CommentAuthorTimber
    • CommentTimeJan 26th 2009
     
    Skywalker,

    Thanks for the input. Indeed, i am sure that these issues have been talked about before, but it is difficult to sift out the pertinant info i such a large thread.

    And as such i am also sure i am added to the guff, but i hoped that some of these questions would bring up important points about the whole MF argument.

    As for my opinions, I am not clever enough to figure all the radiation/convection/conduction agruement, but i do know about some of the short falls in traditional constructions.

    Timber
    • CommentAuthorskywalker
    • CommentTimeJan 26th 2009
     
    Timber

    It was not my intention to belittle your post!

    Just do a forum search on U values, much interest there, similar cast occupying relatively similar standpoints but readable in less than 1/2 a glass of wine.

    As for this thread we should get one of the students that drop in to do a summary for an undergraduate project 'Summarise in 1500 words Biff's amazing thread' - I drop in once a year or so just be be naughty. I remain skeptical of the manufacturers claims as the physics simply does not add up (as has been gone over here so many times). I suspect that the air-tightness/draft exclusion the stuff helps with has more to do with the perceived insulation it provides in the real world than it's thermal properties (and have for some time).

    S.
  6.  
    OK, Where shall I start. Firstly, I'm not going to try and explain in precise detail exactly how multifoils work, bacause a) I dont know in sufficient detail and b) more pertinently, I have been following this thread for a good while and it does seem that the "antis" will not accept any explanation - Fostertom has written at length an awful lot of sensible and scientifically correct stuff, to be met with barrages of abuse and "we dont believe you". I have no doubt that any explanation I try will be met with the same jeers.

    So, anyway, it was more than a loft extension - more a whole new roof. I've a large house, 10m x 8.5m with a small front bay - bedroom & hall. The old roof was taken right off, which comprised the original pitched house roof at the front of the house and the flat roof over the large rear extension. A complete 42 degree pitched roof was put over the whole 10 x 8.5m area, with a couple of rooms in there. It was finished just about 12 months ag now. No problems with buidling control (HIllingdon)

    Its a warm roof construction, with the multifoil over the rafters, then counter battens, then breather membrane, then tiling battens, then tiles. The multifoil is Tri-Actis 10

    In terms of volume it is about 100m3 of new volume - a nice large "playroom", a study, and loo/shower.

    My heating bills have dropped - not massively, but they have dropped. So I've gained 2 new rooms and they have added positive insulation value!

    In general, the radiators in the loft do not come on (TRVs), although I have to admit when it was -5 out, they did come on.

    So what I can say, is that the effective insulation value of the multifoil is very good. Is it better than 200mm of Celotex or whatever?, I dont know. I cant actually do a controlled test really can I?

    In terms of insulation, the architect & I kept the builders honest - lots of stapling - with 14mm staples. All joints stapled onto noggins (they forgeot them). Lots of tape (although I'm unconvinced of its effectiveness), and MOST IMPORTANTLY, getting the detail at the eaves correct - brigning the multifoil down to the wall plate and stapling it, taping at the rafter ends and stapling it, and then stuffing the gap on the inside with mineral wool insulation.
    • CommentAuthorskywalker
    • CommentTimeJan 26th 2009
     
    Dim

    Didn't you do this last August/page 10 already.

    Or is this another loft?

    S.

    PS Just proving I've been awake for some of it!
  7.  
    Thank you for the details, just one last question, is there any insulation in the loft floor?
  8.  
    Congratulations bot, you're the winner of post #500.

    Personally, I think the foils work because of better air tightness detailing than that obtained by stuffing glass/mineral wool batts into somewhat rough openings.

    When I get my hands on an IR thermometer I'll compare a wall I did with "double bubble" with another in pretty much the same general area that was done with 12.5mm foil faced PUR board. I was just as careful with the airtightness detailing both cases. Subjectively, the wall with the double-bubble feels cooler than the one with PUR, but it's hard to say exactly. Both face the same direction and neither gets sunlight at this time of year.

    Paul in Montreal.
    • CommentAuthorbiffvernon
    • CommentTimeJan 27th 2009
     
    Posted By: dimengineerOK, Where shall I start. Firstly, I'm not going to try and explain in precise detail exactly how multifoils work, bacause a) I dont know in sufficient detail and b) more pertinently, I have been following this thread for a good while and it does seem that the "antis" will not accept any explanation - Fostertom has written at length an awful lot of sensible and scientifically correct stuff, to be met with barrages of abuse and "we dont believe you". I have no doubt that any explanation I try will be met with the same jeers.


    I'm disappointed that you're not going to try and explain how multifoils work because, as you may have gathered, I am not convinced by the scientific validity of Fostertom's explanation. I was hoping that a professional engineer might be able to shed further light. Note that my concern is not with airtightness or any of the other possible advantages of multifoils but just with the narrow issue of whether the internal layers of foil provide good value for money in preventing heat loss.

    I do hope you are not implying that I am barraging you with abuse and jeers. I do try to reserve that tactic for those who attempt to promote environmentally damaging building materials and methods on a Green Building Forum :)
  9.  
    Hurrah!

    Celebrations all round, special contribution awards to Tom and Biff, the beers are on Actis and Celotex!!

    J
  10.  
    Posted By: skywalkerTimber
    I suspect that the air-tightness/draft exclusion the stuff helps with has more to do with the perceived insulation it provides in the real world than it's thermal properties (and have for some time).
    S.


    There are cheaper ways to get air-tightness. I have seen this stuff used in cavities - nearly up to the bricks or right on it, rendering the stuff useless against the brick or not.

    The only way to test this stuff is have two identical houses one with multi-foil and one with foam/rockwool insulation. Both with the same level of air-tightness. Then have two families with identical living patterns. Then see what the heating bills are.
    •  
      CommentAuthorrogerwhit
    • CommentTimeJan 27th 2009
     
    Or just two tightly-built dog kennels equipped with sensors and identically programmed heat emitters?
    • CommentAuthorbiffvernon
    • CommentTimeJan 27th 2009
     
    Celebration? Oh, I see we've hit the half millenium!

    Families are never the same so it had better be the dog kennel. But computational moddeling should be easier. It works for complex systems such as nuclear reactor design and global warming so building insulation should be a piece of cake. We just need a computational physisist rather than a builder with a bit of pseudoscience.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 27th 2009 edited
     
    Posted By: biffvernonWe just need a computational physisist
    so that disqualifies you, dimengineer!
    •  
      CommentAuthorfostertom
    • CommentTimeJan 27th 2009
     
    Posted By: rogerwhitOr just two tightly-built dog kennels equipped with sensors and identically programmed heat emitters?
    I thought that approach was held to be the epitome of contemptible unscientificness, compared with the 'scientific' hotbox route? So there's nothing wrong fundamentally, with the famous Actis/BBA twin-shacks approach to accreditation, just needs more rigour?
    •  
      CommentAuthorfostertom
    • CommentTimeJan 27th 2009
     
    Posted By: biffvernonthose who attempt to promote environmentally damaging building materials
    MDF! plastics! cement! power tools! imported anything! electricity!food (80% petrochemical)! human existence! no truck with any of that on this forum, thank you
    •  
      CommentAuthorrogerwhit
    • CommentTimeJan 27th 2009
     
    <blockquote><cite>Posted By: fostertom</cite>I thought that approach was held to be the epitome of contemptible unscientificness, compared with the 'scientific' hotbox route? So there's nothing wrong fundamentally, with the famous Actis/BBA twin-shacks approach to accreditation, just needs more rigour?</blockquote>

    It's the pragmatic approach, especially since no-one can agree on the theory!! If it can be thus shown to work, then it DOES work!! And Tom, such a test would incorporate by default your insistence that dynamic conditions (not steady state) are key.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 27th 2009
     
    I totally agree, rogerwhit - bring it on!
    • CommentAuthorMike George
    • CommentTimeJan 27th 2009 edited
     
    Posted By: fostertomimported anything!


    No, dutch bicycles are ok apparently:bigsmile:
    •  
      CommentAuthorfostertom
    • CommentTimeJan 28th 2009 edited
     
    To further rekindle things, now we have the possibility of re-examination, I found this, from the old forum: http://www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_tuzncnnui_1170338947 . Funcrusher then replied 'Fostertom refuted', but I couldn't follow the maths ... anyone want to comment?

    Actually, now I do understand Funcrusher - and he's right - and my calc results agree with him! So fostertom's not refuted! I think.
   
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