Apart from being easy to handle and install my experience of the stuff is that it works well when only a thin overall build up will fit. For the majority of houses this is not an issue and other (more sustainable this is green building forum) insulation exists. The flammability and electrical behaviour and say assessment to BRE for embedded energy and recyclability and toxicity require further information. I would suggest thin foils adjacent to a cool surface where space is at a premium as on the inside of aeroplanes and in particular (a recent experience) the inside of the hull of a boat all the way up to the gunnels. It certainly does work well with reflection and many other aspects for its size. And with a thermal imaging camera on an open sheet you can see your own heat reflecting off it I didnt compare it too alternatives but maybe this is a better way off seeing it in action in a way that everyone else other than those that know the physics and science can understand?
But when it comes to a house you cant paint on it, you compromise it when fixing and running services through it , you have to leave the room to make a telephone call (maybe a blessing) it burns, conducts electricity and we surround it with other insulation anyway.
regards
thamesrenewables

Thanks for the link to the Period Property forum, Biffvernon.

I have looked at the tri-isosuper 10 website. It is interesting. The BMTRADA certificate is difficult to evaluate. They have used a non-standard test method and there is far too little detail for me to assess what the test is really saying. Anyway, doesn't Part L require an ISO or BS test to validate performance?

The technical spec. says “Thermal equivalent to 210mm of mineral wool when installed in roof applications, as certified by BM TRADA. (Thermal efficiency measured under real conditions by TRADA Technology Limited).” although the qualification “when installed in roof applications” is omitted on occasion, which could be misleading to a casual reader. The U-value is quoted at 0.19W/m^2K.

From the installation guidelines, I understand that Actis is claiming this thermal performance for a construction of Vapour Barrier, 25mm Air Gap, Tri-iso 10, 50mm Air Gap, Roofing Felt. This would require spacer battens of around 40mm and 65mm thickness by my reckoning as presumably the foil squashes down to almost nothing when it is between the battens. So the construction is around 105mm thick overall.

The U-value of 210mm of Rockwool would be around 0.19W/m^2K, so that is not surprising. If we had a perfect, still layer of air, with zero radiation across it, the U-value of a 105mm thick layer would be 0.24W/m^2K at an average temperature of 0degC. So somehow the Tri-iso 10 is doing better than this, which I find very hard to understand. Since air gaps are 75mm worth of the insulation, it is safe to assume their U-value is 0.025/0.075=0.33W/m^2K (provided we have killed all other heat-transfer mechanisms completely). This means that to achieve U=0.19W/m^2K overall, the foil stack must have U=0.44W/m^2K and this translates to a thermal conductivity of k=0.013W/mK. This is about HALF that of air, which forms the majority of the stack's volume!

By the time you have allowed for imperfect air-gaps, and some residual radiation losses, the stack must have a thermal conductivity even lower than 0.013W/mK. On this basis I would have to disbelieve the quoted U-value for tri-iso 10, but perhaps I have misunderstood the technical spec. Can anyone help me out?

Posted By: sparrow Of course, the insulation would be no better than a 30mm layer of still air.

Hi sparrow, If this is the case then it means that it is also comparable [approx] to 30mm of PUR as both have similar k-values. Yes? or am I missing something?

As most of my comments have been about fibrous insulation vs multi-foils, I thought it would be worth summarizing the position of rigid foams.

1. Conduction through foams is potentially reduced by using e.g. carbon dioxide as the gas in the foam's bubbles. (Carbon dioxide has a thermal conductivity only around 60% that of air).
2. Convection within the foam is prevented by its closed-cell structure.
3. Radiation through the foam is reduced by the solid material of the foam, the fine closed-cells, and the low emissivity outer foils that are common on rigid foam boards.
4. Water take-up is claimed to be low.

So from a thermal perspective, PUR/PIR boards tick all the boxes. A nice product. They probably just need fitting carefully to avoid gaps.

Hi Ads. The U-value of an insulator tells you the rate of steady heat flow per unit area for a given temperature difference, hence the units W/m^2K. Another, quite independent, thermal property of a material is its thermal capacity which tells you how much energy is needed to raise 1kg of the material by 1K. The basic units for this are J/kgK (the “specific thermal capacity”). However, for a flat insulation layer of a given thickness, it is more useful to think of how much energy is required per unit area to raise its temperature by 1K, so we end up with a “superficial thermal capacity” with units of J/m^2K.

Thermal capacities only really matter when temperatures are changing. It is possible to have two insulation materials that have the same U-values but quite different thermal capacities. The material with the higher thermal capacity will lead to buildings with longer “decrement delays” and smaller daily temperature fluctuations. It is important to remember, however, that it is not just the thermal capacity of the insulation that matters. Quite often, the thermal capacity of the insulation is small when compared to (say) the thermal capacity of an inside wall. In this case, the decrement delay is determined primarily by the thermal capacity of the wall and the U-value of the insulation, rather than by the thermal capacity of the insulation itself.

An example. Suppose we have a single insulation layer of mineral wool or PU foam with an inner plasterboard wall.

Mineral wool 250mm thick. U-value 0.16W/m^2K. Superficial Thermal Capacity 2500J/m^2K
PU foam 150mm thick. U-value 0.16W/m^2K Superficial Thermal Capacity 6500J/m^2K
Plasterboard 12.5mm thick. U-value 12.8W/m^2K Superficial Thermal Capacity 9980J/m^2K

In this case, 250mm of wool has the same U-value as 150mm of PU foam, but its thermal capacity is less than half as much. But both of these have a lower thermal capacity than 12.5mm plasterboard. Therefore, although using PU foam instead of wool will increase the decrement delay and reduce temperature fluctuations a bit, they will not change by as much as you might expect by simply comparing the thermal capacities of wool and foam.

In a roof of standard construction, I think the insulation with the highest thermal capacity will give you the lowest variations of internal temperature, and the decrement delays are unlikely to be too long. I can't think of any benefit in using a lower capacity material on e.g. a north-facing pitch (other than possibly cost). So foam is probably better (thermally) than wool for this application. Note that multi-foils, with big air-gaps, will have low thermal capacity compared to both wool and foam.

I just feel the urge to give this thread a bump, having just visited a barn conversion site where TriIso10 is being installed at the behest of the architect with, allegedly, the permission of the BCO of North Kesteven District Council, and with the client left bemused at the cost.

Thanks to Andy Simmonds in www.aecb.net/forum/index.php?topic=764.0 :
www.cen.eu/cenorm/businessdomains/technicalcommitteesworkshops/workshops/ws36-insulation.asp and
www.cen.eu/cenorm/businessdomains/technicalcommitteesworkshops/workshops/usersludovicdesktopcw36scopemodified5.pdf

To fostertom, I am intrigued by your comments about the behaviour of conventional and multi-foil insulations during temperature changes “conventional insulation (gd in steady-state temp, useless in dynamically changing temp conditions) with multifoil (the opposite)”. Can you give any explanation of this based on the physics of the materials (or point me to the source of your comments)?

From what I understand so far, one important difference between Cellotex and a multi-foil would be the greater thermal capacity of the Cellotex. In most circumstances the insulation's thermal capacity is probably smaller than that of the surrounding structures, and therefore of limited significance (see some of my other postings). However, I would expect the Cellotex to respond somewhat more slowly to changes in ambient temperatures than an equivalent multi-foil. That is, the decrement delay of the building should be a bit longer with Cellotex instead of a multi-foil. I think this would be an advantage for the Cellotex.

I find it hard to think of another physical mechanism that would cause a conventional insulator to behave badly during temperature changes other than moisture uptake. If the insulator becomes wet then both its static and dynamic properties are likely to be adversely affected. But Cellotex should be pretty immune to this if installed properly.

It is not clear to me why the combination of Cellotex and a multi-foil should be any better (thermally) than a thicker sheet of Cellotex of the same overall U-value.

Tom, surely in your envisioned environment you are totally disregarding the effect of convection, thereby over emphasising the contribution of radiation .
From training years ago but still stuck in my head are the basic %age contributions to thermal conductivity of the 3 main mechanisms i.e conduction, convection and radiation. Radiation being the minor contributor at 20% at temperatures below 50degc. Convection, however, plays a major part as evidenced by the dramatic, well documented and proven changes in thermal conductivity of insulating foams, by decreasing the cell size, changing the blowing agent or of course removing the convection media altogether by pulling a vacuum?

Saint, I'd like to discover where that old figure of radiation only 20%, comes from. Everyone seems to be aware of it, knows it's 'old' but can't say exactly what it relates to. Anyone know?

Convection is covered in the 'full' story-type version www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_wlpssdlpg_1142805843&showpage=120 . Me, I tend to visualise, then I can understand, and as far as I can see the key thing is self-evident - that radiant does almost the whole job, when a fresh temp wave reaches the near side of a cavity, of thermal transfer to the far side of the cavity. Note, that's under dynamically varying temp conditions - not so under steady-state conditions, when I guess the 20% rule might be correct. Put it another way, under dynamically varying temp conditions, all supposed convective and/or conductive advantages of bubble size, blowing gas, vacuum etc become completely irrelevant, as almost all the transfer is done radiantly and completed long before the slower mechanisms of convective or conductive transfer can lumber into action.

Tom, have no false impressions. I have no vested interests and the only turf I defend involves a lawnmower.

I thought multifoils were a smart idea but I couldn't understand how they worked from the physics I knew. So I tried an experiment and found, to my surprise, that my coffee cooled down quicker than I expected. So now I don't think they are a smart idea and neither you nor anyone else has managed to explain how they might work according to physics as I understand it.

So I conclude that:

Draught-proofing can be achieved with a sheet of polythene (among other methods). Convective and conductive insulation can be added by by using bubble-wrap (very cheap). Radiative insulation can be added by using foil faced bubble wrap. The multiple layers of internal foils add very little thermal resistance but a lot of cost (i.e. opportunity for profit taking). Where space is at premium over cost, aerogel insulation such as 'Spacetherm' if more effective.

Posted By: biffvernonneither you nor anyone else has managed to explain how they might work according to physics as I understand it

Biff, can you confirm that you've actually read and understood my explanation, but disagree with all or particular bits of it - if so, which bits? And while we're at it, did you understand and do you concede my explanation/calculation of 'what layers 2-6 do', which disproved the conclusion of your Excel calc? I seem to remember that your coffee experiment involved contact rather than clear airspace between the multifoil and the inside (and outside?) environment(s), which all agree prevents multifoils from working?

Posted By: biffvernonDraught-proofing can be achieved with a sheet of polythene

A single sheet of polythene, or of matt black tissue paper, will also halve the rate of radiant transfer, compared with that between hot body and cold body with nothing in between; three sequential sheets will reduce it to one eighth. Substitute three reflective foils, and radiant transfer is reduced to 1/160. That's how multifoils work, except that everyone rightly points out that there's conduction and convection as well as radiant. 'Everyone' then proceeds to say that conductive and convective so far outweigh radiant, as to make the latter irrelevant. I'm saying that under the specific conditions of dynamically changing temperature, the reverse is true - radiant so far outweighs conductive and convective, as to make the latter two irrelevant.

Posted By: biffvernonaspects which don't accord with my understanding of physics, especially the layer 2-5 behaviour

If you're right that 2-5 don't do anything significant because of sharply diminishing returns, then you'd be right to doubt that multifoils work. But what about http://www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_tuzncnnui_1170338947 ?

Formula supplied by martian, application and result not disputed by anyone so far, the temp differential between hot side and cold side is divided and spread 'near-enough' equally between the foil layers, despite the working of a 4th power, which is insignificant over the small temp range 272K to 293K. QED - one doubt about multifoils, that's had a lot of airtime, gone! What else?

OK, Houdini!

If you sit close to a radiator, don't you feel direct radiation off it? If you put a sheet of glass between, so convection's eliminated, you'll still feel the radiation through the glass.