Multifoil insulation

[RogerS]

I'm wrestling with this one.

I have researched so many threads on different fora that the only thing I can be certain of is that many of the responses and views reflect the vested interests of many of the authors.

I agree that at the end of the day, it's what the BC Officer asks for that I go along with but I would like to understand whether it is all that it is cracked up to be or not.

I have found these two documents on the web. The one from BRE Scotland concludes that the performance of multifoil in a dynamic situation (ie the home) matches the results from the hotbox tests (which the multifoil manufacturers claim do not give a true picture of the performance of multifoil). In other words, the thermal resistance is only a third of what the manufacturers claim.

The second document I struggle to understand as it seems lightweight in comparison and glosses over so much. However, it seems to imply that 30mm of multifoil requires the same fuel bill as 130m of PUR. Mind you, how do you get 30mm of multifoil since it's so thin?

Does anyone else concur with my conclusions?

http://www.tristan.demon.co.uk/images/m ... ly2005.pdf

http://www.tristan.demon.co.uk/images/m ... rt_gbf.pdf

 

[haggisbasher]

Hi Roger

I'm a BCO and I just graduated my degree this summer one of my colleagues did his honours dissertation on the multifoil insulation products available.

His conclusions essentially mirrored BRE. In his opinion and many others as you have found the product has some useful insulation value but not the levels claimed by the manufacturers. About a 1/3rd sounds consistent with what he found.

I have seen it used on jobs i was working on and on discussing it with the project manager he indicated that it wasnt very good to work with. The joiners hated it because it was so fiddly to install. He had to take them off bonus because they couldnt make any money on it. In order to install it properly you have to tape over every edge and tape the laps etc.

IMO if you want to take the edge off the cold in your shed or workshop its probably great but if you want full building regs insulation levels then its not going to do the job

hope thats of some use

Cheers
Tom

 

[RogerS]

Thanks Tom..that's useful advice. It's a balancing act. Time for me is not the issue but losing ceiling space is. My rafters are 85mm deep. Taking off the 25mm airgap leaves me only 60mm of PUR that I can put between the rafters. So to get to the required u value I need to either put additional PUR over the rafters but this eats into the amount of purlin that I have visible.

It's an optical illusion. The more purlin that you see, the larger the room seems. Ideally I'd just lay a layer of multifoil over the rafters followed by plasterboard (but I have a sneaking suspicion that I need an airgap between the two). I'm wondering if I could lay two layers of multifoil?

or maybe Thinsulex which seems to get more 'ticks in boxes'.

 

[haggisbasher]

hi Roger

do you need full building regs standard or do just want to improve the insulation?

My understanding is that 2 layers of the foil wont make any difference, the insulation is derived from the sealed airspace not the material itself, hence the importance of taping laps and edges etc.

I'm not familiar with thinnsulex but its claims seem more realistic than the othrs on the market. I would read the BBA cert closely before committing, the devils in the detail in these things.

Cheers
Tom

 

[Jake]

Phenolic will give you a slight advantage over PUR.

 

[RogerS]

hi Roger

do you need full building regs standard or do just want to improve the insulation?

My understanding is that 2 layers of the foil wont make any difference, the insulation is derived from the sealed airspace not the material itself, hence the importance of taping laps and edges etc.

I'm not familiar with thinnsulex but its claims seem more realistic than the othrs on the market. I would read the BBA cert closely before committing, the devils in the detail in these things.

Cheers
Tom

Full building regs as the cottage is under Building Control Notice...all the gory details in my blog.

Thanks for the heads-up re two layers. I'll double check thinsulex. from what i see it's equivalent to about 30mm of PUR and so I guess the savings are marginal.

Thanks Jake re phenolic

 

[Scott]

The guys who converted our loft put on a great show of Gallic disdain when this stuff was mentioned. No proper explanation given but they seemed to consider it cr*p!

This is a specialist loft conversion outfit in an area that goes from -10 in winter to +30-35 in summer so hopefully they've a bit of an idea what they're talking about.

FWIW etc ...

Know little to nothing about it myself I'm afraid

ATB

 

[RogerS]

The guys who converted our loft put on a great show of Gallic disdain when this stuff was mentioned. No proper explanation given but they seemed to consider it cr*p!

Had to chuckle when I read this as the makers of Triso is Actis - a French company

 

[Scott]

Had to chuckle when I read this as the makers of Triso is Actis - a French company

Aye, that sounds about right! :lol: :lol: