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Green Building Bible, Fourth Edition
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Products: Multifoil Insulation

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  1.  
    Tom,

    I'm not convinced, but without data, there's only opinion. I am in a position to have actual data. My old house was measured at 12.7ACH@50Pas before renovation and 6.5ACH@50Pa afterwards. These are actual measured figures. Looking at my hot2000 reports, it gives this:

    Building envelope surface area 394m2
    Equivalent leakage area @10Pa 3112.87cm2
    Normalized leakage area @10Pa 7.0911cm2/m2
    Airflow to cause a 10Pa difference 776l/s

    F326 required continuous ventilation: 60l/s (0.33ACH)
    Net air leakage and ventilation load: 97.183GJ per year

    Estimated annual energy consumption 84335kWh

    Running the post-renovation house (with all other improvements removed, just the air leakage upgrage) gives

    Equivalent leakage area @10Pa 1593.53cm2
    Normalized leakage area @10Pa 4.0447cm2/m2
    Airflow to cause a 10Pa difference 398l/s

    F326 required continuous ventilation: 60l/s (0.33ACH)
    Net air leakage and ventilation load: 51.830GJ per year

    Estimated annual energy consumption 66368kWh

    So roughly 18000kWh per year saved by reducing the air leakage.

    How did we do this? Replaced old windows which weren't sealed to the walls anymore or had cracked glass, caulked in various places and fitted thin insulation/air barriers internally when we removed cracked plaster and lath and rebuilt from the inside out. Nothing particularly rocket science - and we attacked the big obvious holes first. There's still air leakage (obviously) and I suspect it's even lower now as we've done more work since the second blower door test. But it is clearly worth doing even if you only halve the leakage from what you had. You don't have to get to 95% to see savings - every bit of leakage reduction has a corresponding reduction in energy usage. Of course, I live in a cold climate and require continuous heating in winter (see the outrageous pre-renovation energy consumption figures).

    My current annual energy consumption is now more like 22,000kWh - but that's largely due to the use of a GSHP as the primary heating/cooling system.

    Paul in Montreal.
    • CommentAuthorbiffvernon
    • CommentTimeDec 17th 2008
     
    Multifoil should not be seen as a draught-proofing tool. A single sheet of polythene does this job better and cheaper. To defend multifoil on the basis of reducing air change rate is silly.

    (What is the health effect of quartering air change rates?)
  3.  
    Biff, I don't now about the others but I am saying that multifoil may outperform mineral wool in in-situ testing due to its comparitive air tightness. Something that reflects rather a lot of situations in the real world. The chart shows how this can effect energy use. However, this is merely an example, and most existing houses in the UK will never get close to 0.25ach in my opinion.

    Health effects are another matter and can be dealt with by a controlled ventilation system, should a typical house become airtight enough to warrent inclusion
    • CommentAuthorbiffvernon
    • CommentTimeDec 17th 2008
     
    Posted By: Mike GeorgeBiff, I don't now about the others but I am saying that multifoil may outperform mineral wool in in-situ testing due to its comparitive air tightness.
    Of course it can. But so can a sheet of polythene. More cheaply. The internal foils contribute to cost. Period.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 17th 2008
     
    Posted By: biffvernonMultifoil should not be seen as a draught-proofing tool
    Agreed, not as 'the' explanation for its insulating (or rather, whole-season fuel-need reduction) performance. It beats me how the perforated multifoils work at all. My interest in in the imperforate ones. Then, if using an imperforate one, you have the option to use it as your airtight and/or vapour barrier - but you don't have to.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 17th 2008 edited
     
    Posted By: Mike GeorgeI am saying that multifoil may outperform mineral wool in in-situ testing due to its comparitive air tightness
    Surely you don't mean that's all there is to it? I'm saying that for most, perforated MFs airtightness doesn't exist, so how can it be a factor at all - unless using imperforate MF, as in http://www.box.net/shared/c44irql48e#Xfoil_thermal_test using imperforate MF, where it clearly (and visibly) is a factor.
    • CommentAuthorbiffvernon
    • CommentTimeDec 17th 2008
     
    Oi! I've been misquoted - It weren't me wot said that.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 17th 2008
     
    Posted By: biffvernonIt weren't me
    You're right - don't know why it did that, now corrected
    • CommentAuthorEd Davies
    • CommentTimeDec 17th 2008
     
    Posted By: biffvernonMultifoil should not be seen as a draught-proofing tool. A single sheet of polythene does this job better and cheaper. To defend multifoil on the basis of reducing air change rate is silly.


    Indeed, my comments are an attempt to explain multifoil, not defend it. The next logical step is then, as you say, to consider a polythene sheet. Actually, it would be interesting to try a polythene sheet in one of the Actis chalets but something makes me think they might not be too keen on the experiment.
  10.  
    Rank the following in order of thermal performance:

    1. Multi-foil installed well
    2. 200 Rockwool and polythene vapour/air barrier installed well
    3. Multi-foil installed badly
    4. 200 Rockwool and polythene vapour/air barrier installed badly

    J

    <Edited to Multi-foil rather than 'Actis'>
    • CommentAuthorbiffvernon
    • CommentTimeDec 17th 2008
     
    And don't neglect to add the prices :)
  12.  
    multifoils are also nice, silver and shiny for that space age, high-tech look.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 17th 2008
     
    Posted By: James NortonRank the following in order of thermal performance:

    1. Actis TIS 10 installed well
    2. 200 Rockwool and polythene vapour/air barrier installed well
    3. Actis TIS 10 installed badly
    4. 200 Rockwool and polythene vapour/air barrier installed badly

    J
    2 best; 1, 3, 4 equally rubbish.

    However, change the holey Actis to imperforate e.g. Xfoil, then 1 best, 2 next, 3, 4 rubbish.
  14.  
    Posted By: fostertom
    Posted By: Mike GeorgeI am saying that multifoil may outperform mineral wool in in-situ testing due to its comparitive air tightness
    Surely you don't mean that's all there is to it? I'm saying that for most, perforated MFs airtightness doesn't exist, so how can it be a factor at all - unless using imperforate MF, as in http://www.box.net/shared/c44irql48e#Xfoil_thermal_test using imperforate MF, where it clearly (and visibly) is a factor.


    There probably is more to it than air tightness, but even perforated MF allows less air leakage than say mineral wool, agree? so the in situ tests are partly due to this. agree?

    Other factors? Tas modelling indicates that the emissivity of a shiny surface makes a difference, as does the resistance of air gaps between the layers.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 17th 2008
     
    I think the thing with min wool isn't much gross air penetration through it, or even the thermographically-visible leakage around the ill-fitted edges of it, but general penetration of the loose exposed surface. And that perforated MF pretty much has - well, in lines 100mm apart in both directions.
    • CommentAuthorbiffvernon
    • CommentTimeDec 18th 2008
     
    Posted By: bot de paillemultifoils are also nice, silver and shiny for that space age, high-tech look.
    That's the killer advantage. I'm going for multifoils now.
  17.  
    Im being half tongue in cheek but I wonder if some people buy into this stuff cause it looks like its come out of a NASA lab.

    For my part I hope this debate becomes irrelevant as new materials like aerogel become cheaper.

    When multifoils work it is because they act as effective air barriers and those drafty lofts (wind tunnels) are finally getting some attention.

    Anyone got any success stories with mf that doesnt involve a loft/wind tunnel?
  18.  
    Edited to Multi-foil rather than 'Actis'
    • CommentAuthorJohan
    • CommentTimeDec 18th 2008 edited
     
    Posted By: bot de pailleAnyone got any success stories with mf that doesnt involve a loft/wind tunnel?
    Yes, blankets for exhausted marathon runners! :smile:
    • CommentAuthorEd Davies
    • CommentTimeDec 18th 2008
     
    Ok, so how much heat are exhausted marathon runners losing via convection and, particularly, evaporation as opposed to radiation? Any experiments on how much help thin but emissive blanks would be?
    • CommentAuthormike7
    • CommentTimeDec 18th 2008
     
    Posted By: Johan
    Posted By: bot de pailleAnyone got any success stories with mf that doesnt involve a loft/wind tunnel?
    Yes, blankets for exhausted marathon runners!:smile:" alt=":smile:" src="https:///forum114/extensions/Vanillacons/smilies/standard/smile.gif" >


    How about this:- http://www.blizzardsurvival.com/page.php?xPage=reflexcell-technology.html

    I spent a very chilly night up a welsh mountain in one of these bags - the problem is that the corrugations work fine if they are pulled and held straight, entraping air. If made to take a compound curve, eg round my behind, the corrugations flatten, expelling the air, and then there's just 3 layers of thin plastic providing very little insulation. If say 25% of the bag is flattened like this, it doesn't matter how brilliant the insulation of the remainder is, 'cos there's no heat to keep in! Mmmmmmy ttttteeth are almost chatttttttering at the memory of it. :sad:

    The manufacturer acknowleges that it's the air as does the insulating, and that the foil reflectivity plays a very secondary role. Marathon runners please note.
    • CommentAuthorDeano
    • CommentTimeDec 18th 2008
     
    Hi all,
    Converted my own barn using MF on the lounge walls and roof (high celing etc). Used mineral wool for celing and MF for walls on the rest. Big lounge, underfloor heating etc, represents about a third of total house volume. Rest of house is underfloor downstairs and rads upstairs.
    What a blunder! Main house is ok for heat loss, walls seem to make no difference (heat goes up). Lounge takes more to heat than rest of house! Does stay cool in summer though.
    My own belated hot box test with a science friend found MF to be about 50mm of mineral wool not 200mm.
    MF only works at all because it can be a total envelope with no air leakage but 2l2 can do that for a fraction of the price.
    Cant beat good old mineral and foam combo.......
    Deano.
    • CommentAuthorEd Davies
    • CommentTimeDec 18th 2008
     
    Posted By: DeanoMy own belated hot box test with a science friend found MF to be about 50mm of mineral wool not 200mm.


    Did you actually directly compare MF against mineral wool? If so, did you stop air leakage with the mineral wool?
    • CommentAuthorDeano
    • CommentTimeDec 20th 2008
     
    Hi Ed,
    No, actually compared MF to celotex. And as a failed scientist have assumed 50mm of celotex is same as 100mm wool. Yes you are right MF can be made more airtight than wool, thus I find a combining all elements in the right order work best.
    Anyone got figures to compare Aerogel to wool?
    Deano.
    • CommentAuthorSaint
    • CommentTimeDec 22nd 2008
     
    Deano, Aerogel is about 3 times more thermally efficient than wool. From published figures 0.0135W/mK vs. 0.040 W/mK. I.e. you need one third of the thickness
    • CommentAuthorMatt
    • CommentTimeDec 22nd 2008
     
    Posted By: bot de paillemultifoils are also nice, silver and shiny for that space age, high-tech look.


    After 3 years mine is not...its covered in black dust everywhere. I know, I spent most of yesterday crawling round in my attic area re-taping all the seams with duck tape instead of the stoopid stuff supplied that has become unstuck...mind you half the dust is now up my nose, so it is a bit shinier. Shame I cannot reach about 50% of the roof without cutting a hole in my ceiling.
    • CommentAuthorbiffvernon
    • CommentTimeDec 23rd 2008
     
    Oh you shouldn't leave it a dusty old attic where nobody bothers to clean it. It's great for christmas tree decorations. Big fluffy and shiny stars.
  28.  
    Posted By: biffvernonMultifoil should not be seen as a draught-proofing tool. A single sheet of polythene does this job better and cheaper. To defend multifoil on the basis of reducing air change rate is silly.

    (What is the health effect of quartering air change rates?)


    Posted By: fostertom
    Posted By: Mike GeorgeI am saying that multifoil may outperform mineral wool in in-situ testing due to its comparitive air tightness
    Surely you don't mean that's all there is to it? I'm saying that for most, perforated MFs airtightness doesn't exist, so how can it be a factor at all - unless using imperforate MF, as in http://www.box.net/shared/c44irql48e#Xfoil_thermal_test using imperforate MF, where it clearly (and visibly) is a factor.


    Posted By: Ed Davies
    Posted By: biffvernonMultifoil should not be seen as a draught-proofing tool. A single sheet of polythene does this job better and cheaper. To defend multifoil on the basis of reducing air change rate is silly.


    Indeed, my comments are an attempt to explain multifoil, not defend it. The next logical step is then, as you say, to consider a polythene sheet. Actually, it would be interesting to try a polythene sheet in one of the Actis chalets but something makes me think they might not be too keen on the experiment.


    Regarding air permeability of a multifoil. There is a new BBA for GenX Multifoil which gives a tested air leakage of 0.1m3/hr/m2 @ 50Pa. [only 100 times better than the current breg reuirement for dwellings]:bigsmile:
    • CommentAuthorMike George
    • CommentTimeJan 19th 2009 edited
     
    See Page 5, Section 9 http://www.bbacerts.co.uk/certs/45/4543i1_web.pdf

    Case rests Your Honour:bigsmile:
    • CommentAuthorbiffvernon
    • CommentTimeJan 19th 2009
     
    It says "Thermal performance — when combined with other types of insulation, the product can contribute in meeting the
    U value requirement for a roof (see section 4)."
    Well they got that wrong - it's section 5.
    And does it actually get us any further? Even a sheet of copper "can contribute". Just not very much.
    Good to see that the BBA is not saying that this stuff is the greatest thing since sliced bread or that the internal foils give excellent value for money.

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