Green Building Forum - Multifoil Insulation

Multifoil Insulation

tony — Mon, 04 Feb 2013 17:11:56 +0000

We all think that you read this thread carefully before you spend on foil

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=125&page=27#Item_30

Multifoil Insulation

Mike George — Mon, 04 Feb 2013 18:10:44 +0000

And for a summary of the facts - page 74 here http://www.rcimag.co.uk/rci-oct-2012/#/74/

Multifoil Insulation

jamesingram — Mon, 04 Feb 2013 18:20:18 +0000

So Mike , quick answer , multifoil works fine (does what it claims), yes or no :)

Multifoil Insulation

Mike George — Mon, 04 Feb 2013 18:27:29 +0000

Never a straight answer for that one.

If you are asking about products tested via hot plate - then Yes, predictions are as reliable as any other insulation tested via the same method.

If you are talking about products which rely on comparative testing...I don't want to get sued...

Multifoil Insulation

SteamyTea — Mon, 04 Feb 2013 18:46:29 +0000

Could you explain in detail and with example the last sentence on page 74 please

Multifoil Insulation

Mike George — Mon, 04 Feb 2013 21:29:16 +0000

You mean 'Complementing its airtightness is a Certified Vapour Resistance of 6000MNs/g thus rating as an effective Vapour Control Layer'?

The Mu factor of the multifoil can be calculated from the Laboratory tested Vapour Resistance 6000 (MNs/g) x 0.2 (vapour permeability of still air) / 0.033 (m)(thickness of foil)

= Mu factor 63,634

To put this into context Mu (Rubber) = 10,000 Mu (Polythene) = 100,000

So Mu (Multifoil) 63,634 is a pretty useful Vapour Control Layer.

I should say however that Mu factors for foils vary dramatically. Some manufacturers offer more than one product at opposite ends of the scale as some applications require low Mu factors.

Multifoil Insulation

SteamyTea — Mon, 04 Feb 2013 21:48:31 +0000

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 08:21:11 +0000

Any MF that is held together by quilt stitching has zero resistance to either air or vapour. Don't know if any of the manufs still use quilting, but they certainly did at the time of the infamous twin shacks test. So the 'explanation' given by detractor/sceptics for the decent performance of the MF shack - that it must have been due to better airtightness - were rubbish.

Multifoil Insulation

Mike George — Tue, 05 Feb 2013 09:10:13 +0000

Hi Tom,

As I mentioned above, there are (nowadays) many multifoils with many different properties.

I don't know the history of what was used when and where.

In terms of comparative vapour and air resistances, are you suggesting that mineral wool and the 'quilted multifoil' used in the shack tests had exactly the same values for vapour and air tightness? because if they did not then this will have clearly affected the results would it not?

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 10:51:16 +0000

Posted By: Mike GeorgeIn terms of comparative vapour and air resistances, are you suggesting that mineral wool and the 'quilted multifoil' used in the shack tests had exactly the same values for vapour and air tightness?

Near enough - as in averagely gappy and/or holey, as was the norm back then. I did a little calc, that the total area of the lots of little holes for quilting (measured from a sample) was equiv to one 80mm diam hole per m2! Might even have been worse than the min wool shack.

Posted By: Mike GeorgeI don't know the history of what was used when and where.

The Actis 9 product of that time, which the test referred to, was definitely stitch/quilted - they briefly offered a spot welded alternative called something else but withdrew it.

Multifoil Insulation

Beau — Tue, 05 Feb 2013 12:20:58 +0000

Tom

I still have an off cut of some Triiso super 9. Now I cant test with air but I could make a little test to see how quickly water permeates through it. I realise water and air do behave in the same way but do you think the test would be of any interest?

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 13:15:41 +0000

No - water and air not comparable - surface tension might ensure no water at all drips thro. Instead, put it to your mouth and suck! or just look at all the stitch holes.

Multifoil Insulation

SteamyTea — Tue, 05 Feb 2013 13:44:09 +0000

Why can't you check with air.

Get a hair dry (on cold) and a microphone on your PC push different materials against the nozzle (or make a bag from them would be better as it has a larger surface area), record the noise the hair dryer makes and then analyse that noise with some free software to see what the pitch is. Would work for a comparison.

Multifoil Insulation

Beau — Tue, 05 Feb 2013 15:54:52 +0000

Air can get through the stitching. I fixed some multifoil over the end of an industrial vacuum set to blow. I could not feel the air going through so I put some very fine dust over the stitching which was blown out in places but not on all stitch holes. ST if you can devise a more mechanically based test I am happy to have another go but mics and computers are not my thing

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 16:19:25 +0000

Just

Posted By: fostertomput it to your mouth and suck!

- as gently as you like! The result leaves no doubt.

Multifoil Insulation

Mike George — Tue, 05 Feb 2013 16:48:10 +0000

Does anyone have a pdf copy or a link to the original TRADA Cerificate for the Actis product? Not sure if it has ever been linked to here but not keen on re-reading 800+ posts

There may be some listed properties which may help

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 17:52:20 +0000

Posted By: Mike Georgesome listed properties which may help

Grade 1 or 2*?

Multifoil Insulation

SteamyTea — Tue, 05 Feb 2013 18:10:48 +0000

Posted By: BeauST if you can devise a more mechanically based test I am happy to have another go but mics and computers are not my thing

Do the same and use a set of tuning forks, or a piano

What is brown and sounds like a bell?

(you ready for this)

DUNG

Multifoil Insulation

Nick Parsons — Tue, 05 Feb 2013 18:30:55 +0000

It was always a cracked bell in my day. It went as a set with 'What's brown and steaming and comes out of cows?' The Isle of Wight ferry..... (Works better spoken!)

Multifoil Insulation

SteamyTea — Tue, 05 Feb 2013 19:35:50 +0000

Multifoil Insulation

Beau — Tue, 05 Feb 2013 19:44:23 +0000

Posted By: fostertomJust
Posted By: fostertomput it to your mouth and suck!
- as gently as you like! The result leaves no doubt.

Done that now Tom very tasty I might add. It is safe to say air can pass through the stitching relatively easily. This surprised me as I have been very pleased with it and the wisdom I picked up from this forum is because it is a good airtight membrane.

Multifoil Insulation

fostertom — Tue, 05 Feb 2013 20:15:25 +0000

Consider the pressure of wind, or even internal air buoyancy on a calm day - it's enormous! Enough to shift a yacht or an air balloon. Enough to need sometimes incredible structural wind bracing. Such forces squirt air thro the tiniest gap, but building people seem to think 'it's only a small crack' or that a scrap of sellotape will seal it. Tell that to any other trade that has to manage fluids - sailors, plumbers ...

Multifoil Insulation

Beau — Tue, 05 Feb 2013 20:28:31 +0000

I am not doubting you Tom but if it is not a good airtight membrane and it works well (which in my view it does) then it must somehow be a good insulator in it's own right.

Multifoil Insulation

bot de paille — Tue, 05 Feb 2013 21:23:21 +0000

Except that multi foil tends to be installed behind plasterboard that is taped and skimmed, considerably adding to overall air tighness. Apart from sockets and switches, there wont be air blowing directly up against the MF.

And even if it is very leaky, its a hell of a lot more airtight then what was there before, ie gale blowing through an open attic/roof space. It has been argued that it is this difference that accounts for the large difference felt after MF has been installed.

Multifoil Insulation

Pile-o-Stone — Thu, 07 Feb 2013 10:03:17 +0000

We used TLX Gold, which is a multifoil combined with a membrane and installed this over our rafters. It performs the same job as roofing felt, but also provides an element of insultion and air tightness without raising the height of the roof. We left a 25mm air gap beneath the foil and then installed kingspan between and below the rafters.

Multifoil Insulation

Martian — Wed, 01 May 2013 21:53:06 +0100

Well well well, still scrapping away I see ...
Just thought I would check in to say I'm still alive and kicking.
Best wishes to all.

Multifoil Insulation

Nick Parsons — Thu, 02 May 2013 08:20:09 +0100

Well hello Martian! Welcome back! (or have you always been there, in the background?). I used multifoil for the first time earlier this year. Not a 'choice', but a necessity in the circs. Still a sceptic.

Multifoil Insulation

fostertom — Thu, 02 May 2013 08:32:36 +0100

Hi Martian

Multifoil Insulation

Martian — Thu, 02 May 2013 15:19:15 +0100

I have been rather busy and only reading stuff occasionally but also stayed away from the mulitifoil debate on purpose as it was getting like "Groundhog Day". A new Building Regs application came in a few days ago though and specified "Tri-Iso 10+" and still with some extravagant and unsubstantiated U-Value claim. In the process of checking it out I had a skim over the last couple of years on this thread.
Plus Ã§a change, plus c'est la mÃªme chose ....

Multifoil Insulation

Nick Parsons — Thu, 02 May 2013 16:51:06 +0100

In trying to help a client trouble-shoot re very poor insulation and air-tightness detailing to his new attic conversion I had cause to converse quite a bit with Actis' tech dept, and found no extravagant claims, and a recognition that the usual lay-up on sloping soffits would include Tri-iso 10 *and* Pu/PIR to achieve a compliant U value of 0.18W/m2K. As a cynic still re multifoil, I found the tech dept very forthcoming.