Celotex et al - loses performance?

dishman · 1 Dec 2016

I have recently read that Celotex and any solid insulation of a similar ilk all lose their performance over time. Somthing akin to the material loosing it's gas insulative properties. After 5 years they are said to be not much better than equivalent polystyrene insulation.

I cannot find much out about it, just forum whisperings, which surprises me as I would have thought this would be big news in the building world.

I was thinking of using some foil backed Celotex to insulate a single skin utility room. It is only a small space maybe 2.5 x.2.5m square. But, based on the above, I am now thinking what is the point, why not just use the much cheaper polystyrene.

If I did would this mean I now need a vapour membrane?
Would the polystyrene be pressed up against the brickwork (which already has some form of membrane covering it)?
Or for such a small space, is a rock wool roll better?

freddiemercurystwin · 1 Dec 2016

There is plenty of foundation to what you are saying, though if you speak with the manufacturers about the issue now, as I have, they will tell you that the figures they publish nowadays are for the leaked insulation values ie @ 5 years old. If they're being truthful I can't help you with.

tomfe · 1 Dec 2016

Blowing agent is only a small proportion of the overall thermal performance, the structure of polyisocyanurate is totally different than polystyrene.
Cost to u-value is about the same so if you have the space use eps.

John D v2.0 · 1 Dec 2016

I don't know where the rumours are from but there won't be noticeable degradation! Just use it and enjoy your warm room!

endecotp · 1 Dec 2016

dishman said:
I cannot find much out about it, just forum whisperings, which surprises me as I would have thought this would be big news in the building world.

Try Google? There has been plenty of research into the long-term changes in properites of insulation. Try "polyisocyanurate long term thermal properties". It does get a bit worse over time, but not dramatically.

theprinceofdarkness · 4 Dec 2016

What about the " guaranteed" less then 1% linear shrinkage in its dimensions. Thats a gap of 20 X 12 X 1% or 2.4" down the the front of a 20' wall cavity.
Frank

^woody^ · 5 Dec 2016

dishman said:
After 5 years they are said to be not much better than equivalent polystyrene insulation.

Said by who? Where's the source of this crap?

freddiemercurystwin · 5 Dec 2016

^woody^ said:
Said by who? Where's the source of this crap?

Tis a few years since I looked in to it but there is some truth in the matter and I've long since lost the inclination to google it all again, the gas leaches out leaving a hollow foam board or at least that was the theory.

^woody^ · 5 Dec 2016

freddiemercurystwin said:
Tis a few years since I looked in to it but there is some truth in the matter and I've long since lost the inclination to google it all again, the gas leaches out leaving a hollow foam board or at least that was the theory.

"The gas"?

But surely this boards can be refilled just like plasma TV's could?

tony1851 · 5 Dec 2016

Have a thumb through this - it refers to the slight degradation over time.
https://www.google.co.uk/search?q=T...ials+made+of+rigid+polyurethane+foam+Oct+2006

tomfe · 5 Dec 2016

You know, I always wondered why they had different lambda values for different thicknesses and now I know.

cjard · 6 Dec 2016

theprinceofdarkness said:
What about the " guaranteed" less then 1% linear shrinkage in its dimensions. Thats a gap of 20 X 12 X 1% or 2.4" down the the front of a 20' wall cavity.
Frank

A ventilated anything is a poor place to put rigid insulation anyway. Build a timber frame instead, so you have the OSB and breather membrane keeping most of the air circulation out, then your kingspan can shrink 1% all it likes and good old air laziness can stop convection in the gap that's opened up.. it's never gonna shrink as much as the gap in double glazing, and that's 16mm-20mm as the sweet spot for limiting convection while providing a good insulation gap

cjard · 6 Dec 2016

tomfe said:
You know, I always wondered why they had different lambda values for different thicknesses and now I know.

Different materials (PIR, PUR, phenolic), and different calcs to account for interstitial voids maybe?

Regards the gas leaking out, I don't see it making enough of a difference so as to double the lambda.. kinda like saying double glazing only works so well because of the argon, and once that leaks out your windows only perform as well as single pane. Ultimately, air is a fantastic insulator and the better it can be fixed in place, the better the insulation is. I've never heard of a gas vaunted to be 50% an insulator as air, so my assertion is that there's nothing PIR is filled with that, when it's all leaked out and replaced with air, leaves a sheet 2/3rds as insulative as when it rolled out the factory..

But if the OP really is bothered about it, he can buy all his kingspan from seconds n co, for the same price per cube as polystyrene, install the same thickness he would have as for polystyrene, lose the same amount of space and pay the same amount of money, then he's always going to be ahead of the curve

noseall · 6 Dec 2016

Load of scaremongering bollax dreamt up by disgruntled rivals. The loss in performance may be tangible over 4000 years.

endecotp · 6 Dec 2016

cjard said:
I've never heard of a gas vaunted to be 50% an insulator as air

That prompted me to do some googling: http://www.engineersedge.com/heat_transfer/thermal-conductivity-gases.htm

As expected the best include Krypton and Xenon (as used in windows) and Pentane (as used in PUR boards).

diynot

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Celotex et al - loses performance?

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