Multi Layer foil insulation

[Rob]

Hello all.

I have been looking into insulating our attic space for some time, and have tried various methods with little success. The room has previously been converted into liveable space, with layers of plasterboard screwed direct to the rafters. This has left the rooms (and the house) extremely cold. I have now removed all of the old plasterboard and am looking for a method of insulating. I initially looked at the Tri Iso style of insulation but have read previous posts which cast alternating opinions on the matter. I was wondering if there has been a definative answer on this subject yet?
I have also found a seller on a well known auction website selling insluation under the name of "triple iso 200" which he claims is the same as tri iso super 10, but it is a third of the price. Has anyone else heard of this stuff. Appologies if Im raking over old ground, or stirring up a hornets nest but this is going to be an extremely expensive job and I am keen to get it right first time!
Kind regards
Rob.

 

[biffvernon]

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=2#Item_22 is the current address of the extremely long thread on multifoils.
Throughout the discussion noboby has been able to explain, in terms of the physics, what the internal layers of foil actually do. My conclusion is that they do virtually nothing of use other than provide a lot of profit for the maunufacturers. I guess buying at a third of the price might be regarded as too good to be true, so probably is.

 

[Moneypit]

The plans for another evening get put on hold as the forum prompts yet another tinterweb search. When will my windows get finished now? The explanations on the workings of alu foil seem well described here......

http://www.radiantbarrier.com/physics_of_foil.htm

 

[Rob]

Thanks for your replies.
I have started to look through the 148 pages of text on the greenbuilding forum with much interest. It appears that depending on how you test it, and under what conditions you can prove it either way!
What I am concerned with is less of the politics and physics, but the practicalities. Has anyone out there ever fitted this stuff to their own house? (ie they were around for a significant period after to judge the results).
On paper this looks to be the ideal solution to my problem, and I am confident I can fit it in the correct manner, so would really like some first hand opinions. Anyone?

Regards

Rob

 

[NT]

AIUI multifoils are basic trapped air insulators, nowhere near as good as kingspan et al, with foil which reflects IR back. Thus they can insulate well enough if facing high temp heat sources, which produce lots of IR. But facing PB there is going to be next to no IR involved, and youre left with something no more effective than bubble wrap.

The usual options are polystyrene where its bulk is acceptable, and kingspan where smaller size is needed, eg for insulating loft cons.


NT

 

[biffvernon]

The best material for insulation where lack of room is the priority such as loft conversions where you don't want to lose headroom, is aerogel. It is sold as 'Spacetherm' and distributed by Proctor Group. Info at http://www.spacetherm.com/. Aerogel is made mostly of air, with a little silica to hold it together. Spacetherm has a little polypropelene fibre added to make it into a flexible mat or board, available in various sizes. Thermal conductivity is 0.013W/mK. That's better than any other insulation material available to the building trade. The downside is that it is rather expensive. Spend less and you will need a thicker layer for the same insulation value whatever material you choose.

 

[Lime]

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=2#Item_22 is the current address of the extremely long thread on multifoils.
Throughout the discussion noboby has been able to explain, in terms of the physics, what the internal layers of foil actually do. My conclusion is that they do virtually nothing of use other than provide a lot of profit for the maunufacturers. I guess buying at a third of the price might be regarded as too good to be true, so probably is.

The problem is not just explaining what the insulation does, another major problem is that a large proportion of the public do not understand physics.
The fact that the transfer of heat from one body to another is carried out by 3 means of transfer confuses most people.
(To jog the memory, radiation, convection and conduction.)
However a large number of people think of cold as being something that "comes in" rather than heat being lost.
Specifically the silvered foil is able to do at least two things:
1 Stop some draughts (movement of air) where it is fitted with no air gaps. (convected heat)
2 Reflect some radiated heat if clean and shiny.

The small amount of trapped air in some foil insulation acts as a partial conduction barrier.

The silver foil within the sheets reflects heat from this trapped air.
If the reflective silver foil just worked one way this would be very effective but unfortunately it doesn't. (a major problem) Heat being reflected back into the house is similarly reflected out again by the reflective foil that faces the other way!

Also the reflective surface does not reflect 100% of the radiated heat, it lets some pass through. Dirt on the surface makes this problem worse.

Heat is lost from a house in all three ways but often in completely differing amounts relative to one another depending on the position on the house that is examined.
For instance heat lost through an open window is nearly all convection loss and the same applies to cracks and holes in the fabric of the building.
Whereas heat lost through a tightly closed window is by radiation through the glass and conduction from the room's air to the colder glass surface.
That ignores any loss through latent heat of course.

 

[MdB]

The working of the central foil sheet would depend a lot on the construction of the insulation.

If the insulation was well connected to the foil then there would be little advantage to it being there. Heat transfer would be by conduction so there would be little radiation to reflect.

If the insulation is poorly connected to the foil then there would be an airgap between the insulation and the foil. There would then be a significant heat transfer by radiation which the foil would stop through reflection.

Regarding the test procedures. Do I take it correctly that the standard method of testing (multifoils do badly) uses some form of hot plate from which heat flow is measured? The alternative method (multifoils do well) is to use an insulated tank of hot water and measure its cooling rate?

If I have this correct then it would be very important to know the temperature of the hot plate and tank of water. If the hot plate is say 250°C and the water is 40°C then the IR radiation from the two would be very different. Have a look at the following graph (from my website - I do IR for a business):

A 250°C surface will chuck out a lot of IR in the 4 to 5µm range where as a 40°C surface will be roughly 100x less. Above 10µm the difference is closer to 10x. This means that if the foil is poor at reflecting at 4 to 5µm it will perform badly with a 250­­­°C surface which may explain the difference in results.

 

[Rob]

Thanks for the informative and detailed reply. I am still struggling to find anyone who has actually used this stuff, and would love to hear some first hand accounts.
anyone?
please?

 

[Johneds]

Problem is Rob, that anybody who has used it will most likely want to tell you how good it is. What you really need to know is the bit you don't want to know - the physics.

Your safest bet at the moment is a layer of phenolic foam board. e.g. Celotex, Kingspan or similar. It is tried, tested and the science is well known. You can be fairly sure that you will stop X amount of heat from escaping and therefore you can be sure what you are getting for your money. Unfortunately this is not - at the moment - true of multifoil.

 

[biffvernon]

The working of the central foil sheet would depend a lot on the construction of the insulation.

Even in the ideal case of the layers of foil separated by a vacuum, the internal layers don't help much. Most of the IR is stopped by the first layer, a little is transmitted to layer 2 from where most is reflectedback to the back of layer 1 and a little on to layer 3 etc. The law of diminishing returns kicks in with a vengeance so that more than two layers is a waste of aluminium. You may as well use layers of snake oil.

 

[biffvernon]

Your safest bet at the moment is a layer of phenolic foam board. e.g. Celotex, Kingspan or similar.

Probably best value for money, but Johneds, have you any experience of Spacetherm? Definitely better thermal resistance but more expensive.

 

[MdB]

The working of the central foil sheet would depend a lot on the construction of the insulation.

Even in the ideal case of the layers of foil separated by a vacuum, the internal layers don't help much. Most of the IR is stopped by the first layer, a little is transmitted to layer 2 from where most is reflectedback to the back of layer 1 and a little on to layer 3 etc. The law of diminishing returns kicks in with a vengeance so that more than two layers is a waste of aluminium. You may as well use layers of snake oil.

Sorry Biff. Completely wrong.
If a substance has a temperature above absolute zero it will produce radiation in the infrared. The insulation above the centre foil will be producing radiation if there is an air gap so the foil will be reflecting some of it back. The insulation will reabsorb this reflected radiation and then radiate it out again. All objects operate in this way continually absorbing and radiating heat energy. The exception to this would be a perfect reflector which wouldn't absorb any heat and as such would act as a perfect insulator.

 

[Johneds]

It's interesting stuff Biff. In fact, I've asked Proctor for details of local suppliers as I may specify it on a mill conversion I am currently working on. The mill is only 4m across internally so space is at a premium. Depends on price and supply?

 

[Johneds]

If a substance has a temperature above absolute zero

So if we stay below absolute zero, say like in Newcastle, we're allright then?

 

[MdB]

If a substance has a temperature above absolute zero

So if we stay below absolute zero, say like in Newcastle, we're allright then?

You can't go below absolute zero as you "kana break the laws of physics, Jim" but absolute zero itself is fine (which is here by the way so Newcastle is above absolute zero)

 

[NT]

Thanks for the informative and detailed reply. I am still struggling to find anyone who has actually used this stuff, and would love to hear some first hand accounts.
anyone?
please?

I cant imagine what they could tell you that would be of any use. 'Yes I fitted insulation and its now warmer. Yes I bought the sales line.'


NT

 

[biffvernon]

I've asked Proctor for details of local suppliers

You might have to buy it from them...but they assure me that they have a van They posted me some samples.

 

[biffvernon]

Sorry Biff. Completely wrong.

Er, actually no, but life's to short to go through it all again. It's all in the Green Building Forum thread that I started over a year ago, mostly on the old site. The first 148 pages are at http://www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_wlpssdlpg_1142805843
and then it continues with another 62 pages (so far) on the new site at: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=1

 

[AMc]

The decision was made for me when I was told that multifoils don't conform to building regs on their own at this time.
So I'll be putting celotex or kingspan under my roof when we eventually get going.