With gaps that big appearing something must be wrong. I would speak to Celotex. See if they will come and look.

Used to cause us all sort of problems when it shrank, and it always did.
It also breaks down when wet.

Think it may have been this one:
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=8603

Thanks for the links steamy tea, It appears Cellotex or similar do have issues over the life time of the product.
Shrikage if it dose happen could be catastrophic to the fabric of the building.

Example: 200mm cellotex between ground floor joist with UFH laid on top. Gap start appearing and its going to get very damp on the edge of the timbers in the cold weather.

Jonti, thanks for wool advise, we have used quite a bit of wool on diffrent projects, but i just read the horror stories about moths attacking it. see post i left yesterday.

As a domestic building contractor which ever way i seem to turn, green or conventional possible issues outside my control seem to be arising.

I am going to build a few construction tests for cellotex and see what happens.

Posted By: wilde68Has anyone else come aross Cellotex insulation shrinking??

Is it PUR or PIR and does it make any difference?

I think this is a one off. Maybe a bad batch or seconds sold as new. Do you have any pictures of the between rafter situation Lester? Also how do you know that the Insulation was fitted tightly in the first place?

This subject has been discussed at some length here and anyone claiming shrinkage is common place has not been able to produce evidence to justifty their position (other than anecdotes) On the other hand there is a lot of evidence to the contrary and that shrinkage is taken into consideration by manufacturers, though the previous concerns were about loss of thermal performance. I haven't read anyone claiming shrinkage of the manitude suggested above. 10 - 15mm across a sheet is very serious. If this were commonplace I'm sure there would be a lot more evidence in the public domain already.

Thanks Steamy , but thats not the thread I meant - I cannot find it :(

Borpin, PIR (polyisocyanurite) is a type of PUR (polyeurethane) I believe, so basically the same thing. I think the difference is that PIR is blown with HCFC/CFC gasses and consequently has a poorer lamba value.

Aha, thanks Saint. That explains it better :) I got the thermal performance the wrong way around then - PIR is better.

I thought [wrongly] that PIR was a consequence of the banning of CFC's which resulted in a poorer lambda value. That was presumably just about PUR?

Posted By: SeretCan you explain?

Ah right, thought you wanted to know when the matrix starts breaking down, though I suspect that with a bit of jiggery pokery, along with the materials other properties, you could work out the expansion.
As PU (I use this term as a generic term and I was involved with these materials over 35 years ago) foam contains a lot of air/blowing agent/other gas, much of it trapped, the expansion of air is known (3.43 x 10^-3/(mm/mm.K)) and PU is know (57.6 x 10^-6/(mm/mm.K), it is possible to calculate the internal forces.
Though probably easier to pop a bit in the over and measure it.

Posted By: owlmanWhat is scary about this situation is that some are using bog standard Celotex and/or Kingspan and underfloor insulation, that is under concrete. This is potentially asking for trouble further down the line. I recently went to Jewsons and MKM and another local merchant for some 100mm "load bearing" underfloor insulation like DOW Corning Styrofoam floormate or similar and each time the sales person was unaware that loadbearing insulation even existed. Everone just uses ordinary Jablite or Kingspan was the usual answer. Well not me and anyone who values their work or home wouldn't either, IMO.

I have to say that I have not found any differences in the specification for the stuff sold as 'underfloor' as opposed to generic PIR (unless I have missed something).
(edit) for instance Ecotherm Eco-Versal has the same compressive strength as Kingspan TF70 and both have BBA certificates for use under concrete.

how about phenolic shrinkage , some talk here of it
http://www.aecb.net/forum/index.php/topic,3612.0.html
"Been meaning to reply for a while but haven't been able to track down the article I promised. There is growing concern within the industry about phenolic shrinkage - a phenomenon acknowledged in this article here http://www.ehow.com/info_8315624_risks-phenolic-foam-insulation.html. I have seen pictures of a recent installation in Plymouth where the shrinkage in an EWI situation was pronounced and visible as horizontal lines. When the boards were cut out, large gaps were apparent and the boards had bowed when compared to a new board. Phenolic is also vulnerable to moisture within the existing structure trying to migrate out of the original construction. EPS doesnt have these risks but still requires great skill in ensuring there are no angular gaps at junctions. It also has twice the embodied energy of stone wool or wood fibre alternatives and none of the acoustic and fireproof qualities" posted by Mark Elton

5% to 8% is a huge amount of shrinkage. 120mm - 190mm over the length of a board! I imagine the foil must look really puckered. Do you have any pics? Have you just found this with Celotex or other brands too?

Yes there's something chronically wrong with those boards if they've shrunk that much, check them out with Celotex.
PUR and PIR boards still made here by Kingspan, Celotex, Xtratherm

The 5-8% shrinkage may be volume shrinkage, certainly possible with some elastomer. We often added on 3% to the linear dimensions to take shrinkage into account.
Just had a look at Wikipedia and they say for PIR shrinkage is now 1%.

When I worked in the industry we took contraction into account at the tooling stage, though we were moulding it rather than machining.
To the best of my knowledge it expands and contracts quite a bit with temperature (could get bulging seals in an engine bay quite easily). It is also 'closes cell' so the air is moving too.
It can absorb quite a bit of water, sometimes in the polymer and sometimes into broken cells, not sure how this affects volume though. Should not if it is just filling voids but may if it is reacting with the polymer, though water molecules can sneak into quite tiny spaces, why it is the universal solvent.

It always smells when cut, I have never worried about it, but I think there is a health risk, so take precautions, both health wise and size wise.

It will get smaller over time I am sure and if stressed will take on that new shape eventually. Why it is not my first choice for insulation.

I found that if I peeled off the foil one side of the board, it would warp, so it's obviously under some kind of tension/compression when it comes off the production line and will change shape/shrink given the wrong circumstance.

Posted By: DarylPPIR 'loses' a little gas for a few days/weeks after it has left the factory.
Although it's supposed to cure in the factory properly, we leave it for as long as possible before cutting it to size.

Good luck....http:///newforum/extensions/Vanillacons/smilies/standard/smile.gif" alt="" title="" >

Me to. I got it delivered as soon as I could get it in, but left it as long as possible to shrink, before fitting (which I am still doing (and fed up of)