Posted By: Viking HouseI'll even go to say that when you insulate large areas of a house the heat loss is focused at the junctions and the temperature of these junctions increases, my neighbours house had a rising damp issue that was solved by pumping the beads, heat drives moisture out!

This is a good point: even if the joist ends are further out in the insulation and therefore potentially colder, if the house as a whole is now kept warmer then it's possible that the joist ends will be as well off or even better off, particularly if the beads reduce vapour transport via bulk air movement.

Posted By: Mike GeorgeThe multifoilers tried to do that for decades and in the end they had to toe the line and accept the physics of the situation the same as everyone else

No, they gave up against vested interest.

The new test rigs that would be capable of testing insulants in real-life dynamically varying (rapidly micro-fluctuating) instead of 'never in real life' artificial steady-state conditions, were cancelled near the last minute - because the conventional insulant manufacturers knew that their products would show up badly in those real-life conditions.

The multifoil guys readily agreed that multifoils give pathetic results under artificial steady-state test conditions - but excel the more dynamically varying the conditions. So let's not talk about

Posted By: Mike Georgeaccept the physics of the situation the same as everyone else

The NPL study that was supposed to settle the matter was a shameless piece of 'who's the paymaster' science. They ignored the Multifoil manufs' hypothesis that they were supposed to be testing - heat transmission under dynamically varying conditions - and just repeated the familiar steady-state regime, using the familiar steady-state test rigs. Unsurprisingly, they got the results they were paid to, and the headline 'confirmation' results were accepted unexamined. As a sop to the multifoil manufs, they did run a test wth slowly-slowly varying conditions - as fast as the steady-state rig would allow - and concluded it made no significant difference - as the multifoil manufs would have confirmed.

Don't you know it happens, even with scientists, who are (shock horror) almost like everyone else.

Looks like Tom is right:

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Thanks Dave, I'd lost track of it FWIW.

the precis at least confirms what I said - all done in a steady-state hotbox and lo and behold confirms expectations as well as FEA-type calcs (which were presumably run until equilibriation). So far completely ignoring the (real-world) conditions under which Multifoils are claimed to work.

Then they did 'temperature cycling' runs and the point is, as far as i remember, the period of those cycles was way way slower than the (real-world) quite rapidlly/dynamically fluctuating conditions under which Multifoils are claimed to work.

That's the kind of simplification that scientists like to make, in order to get the repeatable results that are the hallmark of Scientific Method. They may know it's just an initial simplification, but then they forget to come back and re-complexify the model, because it all looks so beautifully convincing. Then the simplified model is called 'scientific' and the real-life phenomena reported are just 'anecdotal'.

Anyone still think that real-world is steady-state? Just watch a WUFI 'movie' which runs a fascinating multi-parameter graph, as fast or as slow as you like, of what's happening heat-and moisture-wise at any given point in the wall 'sandwich', through the course of a year's weather file. No nice progressive diurnal/seasonal curves - they peak and trough like crazy, even with WUFI's coarse timesteps (is it 1hr or 15mins? I forget). In real life there are no timesteps, everything fluctuates continuously, non-linearly, both from gross effects like gusts of wind or sun coming out, and right down to inexplicable quantum variations I should think. It's the 'weather' within a multi-layered medium - bit like earth's biosphere! - and why shouldn't it display the same chaos-theory behaviour?

That range of real-life dynamic fluctuation creates fast-changing/reversing local temperature gradients, however tiny, which are mainly evened-out by instant-action radiant heat transfer within the tiny voids of non-metal materials (and maybe even between metals' molecules) long before slow-acting conduction/convection lumbers into action. So any insulant that's designed to resist radiation above all, can be very effective in blocking those real-life micro-fluctuations, which aggregate into the nett heat transfer that a hot-box can detect. Whereas your typical insulant has little resistance to radiant transfer, in fact its porous surfaces are ideal emitters.

When and if everything settles to a steady-state, however artificially contrived like in a hot-box, then the instant-action of radiant transfer ceases to be important; the 'heavy-lifting' of constant one-way heat is then done by conductive/convective transfer; which conventional insulants are good at resisting.

Therefore a steady-state hot box test greatly favours conventional insulants, awarding insulative performance which is not fulfilled in real-life fluctuating conditions. And of course multifoils bomb completely in steady-state hotbox tests.

Shouldn't there be a thread for this discussion?

OK let's go over there then. I'll copy in my 2 main posts above, then Mike can copy in his (edit - I've done that, kind of), and I'll challenge him on that, and it'll be just like the old days ...

Posted By: Viking HousePeople in cars have accidents all the time and insurance companies continue to insure them, they calculate the risk so younger drivers are charged more

Not totally correct. Young drivers do have more accidents, but risk is calculated on a mileage basis, not a time basis. Just that our premiums are set annually.
They also use Poission Distribution to help calculate risk. There are two main things they look at, early failure (the first crash) and failure frequency (how many and how far apart).
I suspect that, if there is little historic data, then the building insurance use Bayesian methods from what they do know, to set the premium. So, say you have a new product on the market and you want to 'take a guess' at how likely it will work once installed, but there has not been a similar product installed in the UK. All you can do is look at the failure rates (or performance rates) within the parameters that you do know. To fill in the gaps you can use self generated data from a Chi Square test (the expected outcomes).
So, say you know the product works well at mean temperatures of above 18°C, works very well at mean temperatures 22°C and exceedingly well at temperatures above 25°C. You can plot these points and extend the line backwards to UK temperatures, or you can 'take a guess' at what will happen at UK temperatures based on similar problems.
Either way, the risk is higher at the unknown end of the scale. Great when others are paying for it, not so great for the person paying.

Posted By: Viking HouseWell Mike

Tom said he as an Architect would specify full filling the void beneath a timber floor with Leca, I said filling with Leca was no different to EPS beads.

No he did not. Please quote where he explicitly said that.

Posted By: Viking HouseYou keep harping on about the dew point and the moisture that arrives at the dew point by diffusion

No, I did not say that either. Please quote explicitly where I did (the clue is that I did not mention Diffusion) Infact I posted extensively regarding OTHER sources of moisture/liquid penetrations - which you have totally ignored........Why is that I wonder?

Posted By: Viking HouseShow me the 2001 UK building regs that show details for External Insulation

I already linked the publication. Look at the date of first publication on page 2 ....... But just in case I will show you again. It's here - Section2 in2001........http://regulations.completepicture.co.uk/pdf/Building%20Regulations/Construction%20Details/Limiting%20thermal%20bridging%20and%20air%20leakage-%20Robust%20construction%20details%20for%20dwell.pdf

Posted By: Viking HouseYou said in another post that putting in timber grounds into External Insulation was a disaster

Again no, at the risk of boring everyone to tears I did not say that. I did not use the word disaster. I said it was a RISK!. Please quote explicitly where I mentioned the word 'disaster' There is a big difference.

Posted By: Viking HouseTom picked you up on your comment about Multifoil.

In what way did he 'pick me up'? And your point is? Does it have anything to do with polybeads?

Posted By: Viking HouseYou're used to plastering walls where the outer block is classed as wet and the plaster is porous, with External Insulation everything inside the plaster is dry and remains dry.

How on earth would you have the slightest clue what I am used to!? You don't know me. For a start most of the walls I have rendered in my life (and that's more than I care to remember) don't even have a block, never mind an outer one. Because they have solid walls!

So that's a combination of straw men, misquotes, misinterpretations and outright lies.... well done.

Posted By: Viking House
You said in another post that putting in timber grounds into External Insulation was a disaster, I said that we Externally Insulated 100's of houses and often put in timber plywood grounds and nobody ever came back saying the timber grounds had rotted. You're used to plastering walls where the outer block is classed as wet and the plaster is porous, with External Insulation everything inside the plaster is dry and remains dry.

Hi Seamus, just to add to this - I was also under the impression this was the case but saw the following from Parex;

http://www.labc.co.uk/news/rendering-exposed-locations

So with wind driven rain, a modern thin coat polymer modified render could be allowing moisture through within a few hours of exposure. Eye opening. A lot comes down to the details of course and thickness & top coat.

Posted By: willie.macleodSo with wind driven rain, a modern thin coat polymer modified render could be allowing moisture through within a few hours of exposure. Eye opening. A lot comes down to the details of course and thickness & top coat.

Not only with driving rain; in breatheable-rendered (I hope no one would use non-breatheable) EWI, WUFI shows that at many times/conditions the outermost bit of the EPS or whatever will be at or below dew point of the water vapour that's in it (whether that vapour is currently driving inward or outward) and so it will be full of liquid water - just that outermost bit. But then it soon enough 'dries' out again.

Timber in that outermost zone might survive that alternating wet-dry treatment, but I wouldn't risk it. My guideline is to have at least 40% of the insulation thickness outboard of any timber, OSB etc.

Note that rendered EPS EWI is extremely reliable despite this frequent wetness of its outermost thickness - it's inherent, and none the worse for that.
Even in freeze conditions - it doesn't cause spalling, presumably because the water is held in thin capillaries between compressible granules of EPS - plenty of space for freeze-expansion, harmless.
And yes EPS loses 22% of its insulative value when completely water-logged - but a) in these conditions it's far from water-logged, barely more than surface-wetted; and b) the insulation is only degraded in its thin(ish) outermost bit - and WUFI takes that degradation into account.