Moisture content in the materials when built?

The images everywhere show the GF leaking heat due to edge/incontinuities, while the continuous MF suffers much less from this. Consequently the reports says "the external surface temperatures were higher of the glasswool which appeared to allow more heat to permeate through to the outer skin of the test house than the area insulated with Xfoil". That's out of order because no one seriously suggests that MF is better than 200 GF, just that it's comparable or equal.

Look instead at the centre of the areas of GF away from the leakage edges. There the colour seems same as the MF areas - comparable or equal.

Next suggestion is that interstitial condensation is degrading the GF, giving MF the advantage.

Saint, I don't see any possibility of internally-originating moisture source. Assuming it was a shed built outdoors on a cold day, can we assume that before heating began, inside and outside air was the same? If so, unless both were at or near saturation already, then just heating up the inside air does nothing to increase internal water vapour molecule concentration, and actually reduces internal RH - so where's the 'drive' to cause outward migration of vapour? Even if it did , I don't see how it would reach dewpoint - unless internal and external air were already at dewpoint before heating began.

Alternatively, Mike George says moisture in the construction and Saint asks how long built before the test? Assume long enough for both sets of insulation to equilibriate as far as atmospheric moisture uptake. As it happens, Xfoli is almost the only make of MF that can form a vapour barrier, being imperforate - all others are peppered with stitch holes. Assuming both MF and GF contain equal structural moisture concentration before heating begins, how then is the GF more disadvantaged by interstitial condensation than the MF?

Once again, I feel the fatal tendency of members of this forum to nitpick evidence to death, so as to not even smell the possibility of something new. Absolutely right to criticise the detail, and sceptically remember the prevalence of pseudo-scientific scams down the ages. But for every crit, I'd like to see acknowledgement that something here just may be true, if properly proved. Absence of interest in the latter just looks like psychological desire to cling the the security of staus quo. Why isn't equal criticism directed at the equally flaky science of the hotbox test, instead of this entrenched bad-science/good-science name-calling?

I guess this should report soon..

http://www.cen.eu/CENORM/sectors/technicalcommitteesworkshops/workshops/ws36-insulation.asp

Results due between Oct 08 and Apr 09.

Tom,

I don't think questioning whether there is a vapour barrier could be termed "nit picking". Its just about the most important consideration for anyone involved in insulation.
I hope the test has been done correctly, maybe just badly installed. I've no particular axe to grind with multifoils, personally I wouldn't use them but that is purely because they are unproven to date. A test like this, if flawed, merely compounds that feeling.

Your response to moisture vapour is wrong. The construction is an envelope albeit unsealed which throughout the day fills with ambient air, the RH is irrelevant at this point. We all know that as air cools it is unable to hold the same amount of vapour this then condenses out. Thus if there's no vapour barrier it permeates through the mineral wool and condenses on the colder Versa board.

Surely you've seen Ray Mears or one of his contemporaries collect water in the desert overnight. Dig a hole, place a bean can centrally in that hole, eat all the beans first, that's why its good to do this in a desert, stretch a plastic sheet over the hole, secure the sheet around the edges of the hole and place a small pebble in the centre of the sheet above the bean can to create a concave surface. Lo and behold in the morning you can see all the condensate still running down the inside of the plastic sheet and dripping into the can. Thats the same effect

Ah I see what you're saying. The internal and external air temperatures were the same before the heating period and the building was effectively sealed. Well I can't challenge that as I have no way of knowing. Slightly doubtful and the tests commenced at the end of the day so the inside could have warmed during the afternoon but who knows....bad science?

Perhaps Keith could run a pole on this one...?

J

Biffvernon.
I will try to explain the reason for the internal layers... They are essential to avoid heat transfer by convection between the front and back face of the multifoil. The Temperature difference between the 2 outer layers can be 8 to 10c, and this would create convection of heat (& susequent lower performance). By introducing the layers, the temperature differential is drastically reduced, as each air layer is that much thinner, and has a much lower temp difference, so much so that convection is unlikly to occur, or be marginal. I have a degree of technical knowledge in this subject (with no commercial bias as i do not work for any manufacturer) and happy to share with other interested parties.

I cannot believe some of the claims made by manufacturers, and believe that a Multifoil combined with a traditional insulation is the best option, as all bases are covered. R values as high as 5 to 6 cannot be scientifically proven. The in situ tests used so far have only compared multifoil performance to glass fibre, why not a rigid insulation such as Celotex. The test method for the glassfibre had it open to the room, and no slaters felt or vapour barrier, plasterboard in place. So heatloss through convection was allowed to take place. The multifoil however was thoroughly sealed, and peformed well in comparison, hence the derived R Value being the same as 200-270mm of glassfibre.

Why not compare to a similary sealed Celotex product, or install the vapour barrier, breathable membrane and plasterboard. I suspect a different set of results would be dicovered. I eagerly await to see the outcome of the consultsation on testing, at least to bring some parity and fairness to the table.

I wonder if multifoils combined with aerogel could be the ultimate answer. Especially for those needing to run their houses at 1000 degC!

http://www.techbriefs.com/component/content/article/3273

I also note from a visit to my local builder suppliers that they do not sell Triiso10 any longer as it does not meet the specs. They do sell TLX Silver (thinsulate) but this needs to be combined with 70mm PUR to achieve the building specs of 0.2. I also note that they are bringing in a breathable version TLX gold but this is not yet in production (samples only). This material can be used instead of roofing breathable membranes, it specs 1.011 m2K/W core resistance and 0.16 Emissivity.

My guess is that Multifoils are going to win over PUR on breathability and for fitting into awkward spaces e.g. sloping attic roofs.

Posted By: BrianRI wonder if multifoils combined with aerogel could be the ultimate answer.

Aerogel has about the highest thermal resistivity of any material made so far and will doubtless feature more in buildings if costs can be reduced, but until theoretical physics can explain how the internal layers of a multifoil can produce a significant effect, we should regard it as snake oil. Adding snake oil to the medicine does not give a better cure.

Where do you expect the condensation to occur Colin? Do you mean on the 'warm side' surface?

Seems I'm wrong. Celotex recommend a vapour permeable membrane is used with a warm roof construction.

http://www.celotex.co.uk/downloads.asp?i=2

Biffvernon.

Heat transfer takes place between the front and back layer of a multifoil, fact, otherwise they would defy science. By adding these additonal layers this heatloss is drastically reduced. The number of layers required is balanced up by the function and type of the wadding. Trying to add constructive comment here, nothing else.

I have seen results of many tests with just 2 layers, and subsequently with 3, 4 or 5 internal layers. Its a fact that without the additonal internal layers more heat is lost. Ideally if only the front and back layer is required the product would be cheaper, and more competitve etc.... So it would be the best commercial solution. These additonal layers add cost and complexity to the product, from a manufacturing and packing perspective. There is a lot of testing taking place presently, most of it proving commercially useless, but each time the combination of wadding and number of layers is critical. I'm not a scientist, just passing on observations i have seen with my own eyes.

If you have any idea how to remove these layers and stop this convection and conduction then please let the manufacturers know. I'm sure we could all do with lower cost products.

As for breathability, the TLX gold uses traditional breathing membrane technology to allow the passage of vapour, not holes. I believe it is designed for upgrading the performance of existing roofs, where internal linings are in place and good vapour control cannot be certain. When a multifoil is on the outside, if a reasonable level of insulation is mounted below, it makes the surface of the multifoil cold and potentially at risk from condensation. This is not down to lack of performance of the multifoil, but due to the performance of the insulation below, and the effectiveness of the Multifoil at stopping vapour.

I do not represent any manufacturer, but get to see testing from time to time as an impartial observer. I have a passing interest in anything new, hence watching how things progress.

biff,

I too am a scientist and an engineer. YOur argument is a bit irrational, as you suggest that manufacturers are deliberately adding complexity to a product, that they know doesn't work, to make it more expensive, so its less competitive.
Sorry, that really does not make any sense to me. IanUFH's explanation made perfect sense to me.

I have to say that I have a nice new loft with a multifoil insulated "warm roof", and it works. The proof of the pudding etc....

Tim

Posted By: dimengineeras you suggest that manufacturers are deliberately adding complexity to a product, that they know doesn't work, to make it more expensive, so its less competitive.

Sounds just like the cosmetics industry. Selling cost and manufacturing cost are not necessarily related at all. Some people will pay a premium for certain goods because they are expensive (tautological argument, I know, but it's true).

Over here in North America, there are no multifoils - just products like "double bubble" which has exactly 2 foils - one on either side of two layers of bubble wrap. Popular for keeping heat out of attics and is a good air and moisture barrier too.

Paul in Montreal.

I have no specific information as to how the multifoil works, except as a combination of trapped air and reflected radiation, as described in several of the previous 388 posts. It thus reduces radiation, conduction and convection. It seems to work very effectively in real life situations. I suspect a big part of it is the elimination of air leakage, as its a hell of a lot easier to seal than block insulation

My loft "conversion" was a new construction, the old roof came right off & a new one built. We specified Multifoil to save space. It ended up as a complete cover of mulitfoil over the rafters, rather like a tea cosy. The main issue was getting the builders to staple & tape it properly. The key detail is at the eaves where you have to work something out to prevent a gale!