Green Building Forum - Multifoil Insulation

Multifoil Insulation

fostertom — Thu, 29 Jan 2009 17:42:14 +0000

Funcrusher - are you still out there? I a'waiting with my six-gun!

Multifoil Insulation

funcrusher — Thu, 29 Jan 2009 18:13:27 +0000

Fostertom: I have not been following this new thread, but neither have I altered my thinking since last contributing on the old thread, so cannot really comment further

Multifoil Insulation

fostertom — Thu, 29 Jan 2009 18:49:17 +0000

Godd - because I said

Posted By: fostertomActually, now I do understand Funcrusher - and he's right - and my calc results agree with him! So fostertom's not refuted! I think.

You said:
WE KNOW: t1>t2>t3>t4 - I agree
(t1-t2) < (t2-t3) < (t3-t4) - I agree
as you proceed through the layers from the hot side, not only does the temperature decrease, the temperature fall accelerates - I agree
but not by much -

"despite the proper application of fourth-power, [T(n+1) - Tn] comes out at 3K +/- 10% for all foil pairs. That *is* "near enough" linear, as a useful approximation within the limited range 272K to 293K.

Still, never mind that, the point is that the foils' steady-state temps are "near enough" linearly (evenly) spaced, *not* as Biff, Martian et al have been saying, all bunched up at the hot side, diminishing "near exponentially" (funcrusher) to insignificant for foils 2-6."

Multifoil Insulation

silverback2 — Tue, 17 Feb 2009 15:02:48 +0000

This is a huge thread to go through - so I'm just going to bash in my query.
I saw the Kevin McCloud programme and have been looking for this 'space age' technology every since. I am very disappointed that the forum's opinion is that it doesn't seem to be the answer I need.
I want to (re)insulate my loft and saw this foil as the answer from heaven because when the house was built, the builder fixed all the pipe supplies (gas, water) to the top of the bottom rails of the roof trusses, the plaster for the ceilings below being fixed to the bottom of these bottom rails. I was hoping to use this foil stuff to get the 'same insulation benefit as 25cm of glass fibre' but with the additional benefit of it fitting in the space underneath the pipes.
So, if I insulate to the government recommended level which I understand is now 25cm what do I do about the pipes? (I currently have about 10cm in 'most' places, but certainly not all, which begs the question of what do building inspectors actually do when houses are being built?)
The options seem to be:
1. Squeeze the 25cm insulation underneath the pipe, compressing it to about 7-8 cms. in these areas.
2. Cut the insulation either side of the pipes. (and squash some underneath the pipes?).
3. Lay the insulation in the space, going over the pipes, thus hiding them and making it infernally difficult to access them when needed?
Thanks
Silverback2

Multifoil Insulation

Deano — Tue, 17 Feb 2009 16:48:32 +0000

Dont do it. Foil doesn't work! You have the room, stuff in loads of fiberglass!
No theory or tests, just used the stuff on half the house and guess what, its the cold half!

Multifoil Insulation

joe90 — Tue, 17 Feb 2009 19:23:34 +0000

Hi everyone,

Done some investigating on this subject myself (but have not read all this thread as I dont have the time!) but make up your own mind as I did, have a look at this:-

http://www.foam-insulation.co.uk/insulation/multi-foil-insulation.htm

Thanks

Joe90

Multifoil Insulation

betterroof — Tue, 17 Feb 2009 21:04:02 +0000

This is a pain in the ass! I would really love this to work. I don't follow all the maths yet - can we just do an independent test? how hard would that be? I'm game

Multifoil Insulation

betterroof — Tue, 17 Feb 2009 21:18:22 +0000

oh, ok, just read up some more. is clearer now.

so, what is the consensus (do we even have one, or is in-fighting the order of the day )

Is it ok to use these alongside other insulation materials, to help with airtightness and thermal bridging - or is it pointless? Would it not be better to use something like isolair?

Multifoil Insulation

fostertom — Tue, 17 Feb 2009 22:46:06 +0000

Posted By: joe90have a look at this:-

http://www.foam-insulation.co.uk/insulation/multi-foil-insulation.htm" >http://www.foam-insulation.co.uk/insulation/multi-foil-insulation.htm

talk about the pot calling the kettle black!

Multifoil Insulation

betterroof — Tue, 17 Feb 2009 23:16:18 +0000

yeah, interesting reading tho. it does seem a tad tricky finding unbiased reporting don't it!

Multifoil Insulation

peterglanfield — Wed, 18 Feb 2009 13:14:36 +0000

Sorry to bring the level of the discussion briefy downwards for the benefit of someone outside the trade.....
I have tried to absorb some of this very long thread whilst looking for references to super-thin insulating material (2-3mm?) that would be suitable for the internal faces of our external walls. We live in an 1850s house with solid walls approx 250mm or more thick, good windows and well-insulated loft. But is there anything cost effective I can put on the internal (plastered) faces of the external walls to keep the heating bills down? The approx 25mm thick internal cladding one generally sees advertised would mean real problems with skirting boards and ceiling cornices. Any help or suggestions here would be really appreciated...

Multifoil Insulation

biffvernon — Wed, 18 Feb 2009 14:16:15 +0000

No there is no such thing. It's the way the laws of physics are arranged in our particular universe.

Multifoil Insulation

betterroof — Wed, 18 Feb 2009 18:03:53 +0000

Unfortunately not no. If you want to address heating bills I'd look at other avenues first. You need to insulate your roof as much as possible and look at windows and doors. You want at least double glazed units all round, with really good draught proofing on all doors and windows, internal aswell. then you need to look at the heating systems that you use. Most of this is going to cost a bit to sort out, but long term savings will become apparent.

Grants area available for some of this, so contact your local council. You can also visit these guys

http://www.sustainable-energyacademy.org.uk/

They have show homes you can visit in most areas to get ideas and support, I'd recommend it anyhow...

Multifoil Insulation

Duncan — Sat, 21 Mar 2009 13:05:15 +0000

Sorry to resurect this mind blowing topic...
But....
having read through over 100 odd pages I am still confused.
It may help to explain my circumstances:-
I recently became the proud owner of a 1930`s brick built semi. Previous owners have partially dragged the house into the modern world. However the loft is a different story. It has 4inch ceiling joists filled with fibre type insulation (too old to now identify) It then has a glued (boo) and screwed chipboard floor. This insulation is clearly inadequate, but I am not to keen on lifting the floor (glued remember!). Naturally my thoughts are to consider insulating the rafters. But, the rafters are only 4inch too. My understanding is that I should leave a 2inch air/ventilation gap before any insulation - this only leaves me with 2inches to play with (no smut please).
Clearly until stumbling across this "war and peace" thread I was going to use this foil bubble type of insulation.
Now I am not so sure...
additional information you should be aware of is that I wish to use the loft for a model railway and so want to avoid (if possible) robbing any more interior space by over battening

Please could someone explain in English my options... I want to further insulate my home but also prevent the sun from overheating the loft in the summer. Will this product do both??

Thanks people and sorry for such a long first post!

Multifoil Insulation

betterroof — Sat, 21 Mar 2009 18:26:02 +0000

HI Duncan,

Can I get a bit more info? what is your roof covering? what sort of felt do you have, are there any windows?

You do have a couple of options - you are correct about the ventilation gap being important but you can work around this quite effectively. You already have some insulation in the floor so you have what is called a 'cold roof'. what you are intending to do is add a 'warm roof' style insulating layer at the roof pitch. I would recommend using 50mm insulation board between the rafters, leaving your 50mm air gap on the external face and then finishing the interior with insulated plasterboard. This means you will only lose about 20/50mm on the internal face of your rafters. If you are going to board off the eaves you can put extra loose insulation in there too.

If you don't have windows I would definitely recommend installing a couple of velux - as well as providing natural light you will also have good ventilation in the summer, which you will need. If you don't want to/can't do this then get a roofer to stick some vents in so you get some air movement.

Drop me an email if you want and I'll be happy to help

Multifoil Insulation

ralphd — Mon, 23 Mar 2009 16:52:51 +0000

I've been thinking lately about 2D & 3D heat conduction modeling vs traditional 1D. I think this applies to multifoil insulation. The dominant mode of heat transfer in a multifoil is probably through the scrim that separates the foil layers; the scrim is in essence a thermal bridge between the thermally conductive foil layers.

A steel stud wall is another example of this issue, and ORNL has a nice caclulator to model them:
http://www.ornl.gov/sci/roofs+walls/calculators/modzone/index.html

To use an extreme example, I've seen industrial buildings built of structural steel studs (~16 gauge) with exterior metal sheathing and fiberglass batt cavity insulation. In such cases the cavity insulation is a waste since over 90% of the heat transfer is through the stud & metal sheathing.

-Ralph

Multifoil Insulation

fostertom — Mon, 23 Mar 2009 21:35:48 +0000

On a micro scale, what if the 'scrim' surface consists of lots of little fibre ends that make v small (negligible) point contact with the foil? Would that be conducive to conduction(!) or would heat have to transfer from the foil to the solid fibres mainly by radiation and a little convection?

Multifoil Insulation

ralphd — Mon, 23 Mar 2009 23:07:24 +0000

Posted By: fostertomOn a micro scale, what if the 'scrim' surface consists of lots of little fibre ends that make v small (negligible) point contact with the foil? Would that be conducive to conduction(!) or would heat have to transfer from the foil to the solid fibres mainly by radiation and a little convection?

The scrim you are describing starts to sound like the silica matrix of an aerogel; in which case you don't really need the foil; just the aerogel.
As for the mode of heat transfer from the foil to the fibers, there would be little radiation since aluminum (I'll stick with the more efficient spelling without the extra 'i') has an infrared emissivity around 0.04%. The space between the foils is too small for convection, so that leaves conduction through the air spaces and through the scrim as the dominant mode of heat transfer.

Besides some of the links posted in the aerogels thread, the book "Cryogenic engineering" by Thomas M. Flynn has some good stuff in it; some of it you can read for free online through google books.

-Ralph

Multifoil Insulation

Duncan — Tue, 24 Mar 2009 09:44:11 +0000

Posted By: betterroofHI Duncan,

Can I get a bit more info? what is your roof covering? what sort of felt do you have, are there any windows?

You do have a couple of options - you are correct about the ventilation gap being important but you can work around this quite effectively. You already have some insulation in the floor so you have what is called a 'cold roof'. what you are intending to do is add a 'warm roof' style insulating layer at the roof pitch. I would recommend using 50mm insulation board between the rafters, leaving your 50mm air gap on the external face and then finishing the interior with insulated plasterboard. This means you will only lose about 20/50mm on the internal face of your rafters. If you are going to board off the eaves you can put extra loose insulation in there too.

If you don't have windows I would definitely recommend installing a couple of velux - as well as providing natural light you will also have good ventilation in the summer, which you will need. If you don't want to/can't do this then get a roofer to stick some vents in so you get some air movement.

Drop me an email if you want and I'll be happy to help" start="fileopen" height="15" alt="" isMap="false" hspace="0" loop="1" src="http://www.greenbuildingforum.co.uk/forum114/extensions/Vanillacons/smilies/standard/bigsmile.gif" width="15" vspace="0">

Joe - thanks for the input - I have sent you an email but just in case please see below:-

The property is a semi detached brick built 3 bed semi. It has a newish roof (replaced approx 5 years ago)

Roof construction is pitched with roofing felt and Marley tile over. Currently no windows in roof and we donâ€™t really want any! Eaves are extremely well ventilated on all 3 elevations. This is achieved by an air gap between wall plate and felt. Being an older property this gap varies between 10mm and up to 65mm! â€“ hence I have recently evicted a pile of sparrows (due to non payment of rent/wild parties etc) â€“ Gaps now sealed with wire mesh to maintain ventilation.

My understanding is that given the current high airflow I would not require any vents in the roof or ridgelineâ€¦

My ideal solution would indeed be to

1/ create a warmer loft less prone to extreme heat in summer (?lol!) and extreme cold in winter

2/ increase the heat retention for the house

3/ maintain the current ventilation but restrict it to behind the insulation up the roof and over the top and down the other side â€“ if you understand me

4/ not further reduce the loft space too much â€“ as I said long term I would like a model railway up there and currently the useable bit is only about 3m x 3m (not as big as I would like!!!)

You mentioned insulating the 50mm and then overboarding with insulated plaster board. â€“ I take it you are not impressed with multifoil either!!!

What material would you suggest for the insulation? How would I maintain the airgap if it is a flexible material?

Thanks

Duncan

Multifoil Insulation

sinnerboy — Wed, 24 Jun 2009 13:24:39 +0100

The last word ?

http://arbota.com/insulation-test-ruling-hits-multi-foil-producers-23765/

Multifoil Insulation

biffvernon — Wed, 24 Jun 2009 17:08:10 +0100

I doubt it :)

That article started out at http://www.building.co.uk/story.asp?sectioncode=748&storycode=3143234 but it doesn't seem to be on the DCLG website yet.

Multifoil Insulation

fostertom — Wed, 24 Jun 2009 20:14:44 +0100

There's multi foil insulation and multifoil insulation threads current - this discussion is happening on both.

Multifoil Insulation

biffvernon — Wed, 24 Jun 2009 20:25:23 +0100

There's only one true multifoil thread. The other is a young upstart, a mere imposter.

Multifoil Insulation

joe90 — Wed, 24 Jun 2009 21:03:47 +0100

I have to confess that I dont like/cant see the aurgument for multifoil insulation, However my brother-in-law runs a motorcaravan building company (very successfull) and they use multifoil insulation to stop their vans overheating!!. It all started with a proud new owner taking their van to spain in August and by the time they returned all the internal fittings were distorted because of the excess heat. They did have minimal poly insulation (25mm) but this failed to deal with incoming heat. Since using the multifoil thay have had no complaints. Perhaps its reflective properties are best suited to high temps.

Multifoil Insulation

WatchIt — Thu, 25 Jun 2009 15:40:32 +0100

Surely it will cause condensation if you put a multifoil on the underside of the rafters (or PIR boards between the rafters) with glasswool at ceiling level.

You would be putting a vapour impermable layer across the cold side of the wool, just as you would have had with the old felt, but that had ventilation underneath it.

You should use permeable stuff like wool. If you want to use something on the rafters then again something permeable, TLX Gold is the only one I've seen so far, so that water vapour can still pass through into your ventilated rafter space.

Multifoil Insulation

trolleyed — Wed, 08 Jul 2009 17:23:37 +0100

I've been reading lots about this multifoil stuff and on the face of it - if there was a supplier that undertook a test in accordance with BRE443 to give an R value then we'd be laughing.

So I did some digging. SF40 from Superfoil claims an R value independantly tested - R Value=3.564
Sounds great - but I'm concerned that no matter how hard I try, I can't get them to produce the test results, certificate or other factual information. This concerns me as for all I know Superfoil could be making it up to get sales! I don't think they are but the proof is in the paperwork.

Has anyone else had any better luck than me?

Multifoil Insulation

fostertom — Wed, 08 Jul 2009 19:14:19 +0100

The point is, everyone including the manufacturers knows that multifoils give pathetic results under BR443 methodology, which deliberately substitutes artificial steady-state conditions for the real-world dynamically-varying conditions under which multifoils do work.

Any multifoil manufacturer that claims good hotbox-derived performance for multifoils is puffing.

Having said that, very special testbed-special multifoils have been produced, that are custom-designed to do well when hotbox tested to BR443, and hang the real-world performance, just to prove the point that this is how conventional insulations are designed - but these are far from commercial, tho may be a pointer to the future.

Multifoil Insulation

trolleyed — Fri, 10 Jul 2009 22:08:13 +0100

I guess superfoil potentially has the edge in a BRE test as it's 60mm thick itself. Just wish I could get the "proof."

Multifoil Insulation

biffvernon — Thu, 16 Jul 2009 20:14:51 +0100

In respose to http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4283&page=1#Item_5

Quiet! Moi!

I just didn't think your answer made sense and was too polite to say so.

Multifoil Insulation

fostertom — Thu, 16 Jul 2009 22:52:08 +0100

Ever ingenious, you've created a diversionary game of hyperlink ping pong - still no response tho!