Chasing in kitchen

[ban-all-sheds]

These are closed-cell foams and rely on holding the gassing agent within the cells for their insulating properties and if water vapour could migrate through the structure then the insulating gas would be able to do the same and bingo - poorer insulation.

Have you looked into how these foams lose gas, and suffer a drop in performance, over time?

My belief is that the foil applied to the boards is simply marketing , to attempt to blunt the sales of multi-foils by showing/confusing the unknowing punter with a "similar" shiny surface. Have not seen any explanation for this in their literature.

Is this a belief shared by anybody else?

 

[Rusty10]

Hi everyone, thanks for all the comments, for clarity the boards are 27mm

http://www.british-gypsum.com/produ...es/gyproc_thermal/gyproc_thermaline_plus.aspx

I think the ideal solution as mentioned would be to chase into the board and use expanding foam in the gap...?

 

[mointainwalker]

@Rusty10

If no answers to the contrary, I would say go with that ( but then i did suggest it )

I apologise for the scuffle on the side=lines which often happens, but which i think is valuable as it does often dig up areas of interest around the original question that is beneficial in longer-term general-knowledge for readers.

 

[mointainwalker]

@banal

In common with many forums, this one works best with a degree of reasonableness.

Whilst your reasonableness can be compared with commander Spock ( apologies if rank wrong, we were so poor only could afford electricity to watch it once per month ), others see it a different way.

You put to me that PIR, PUR absorbs water, I reply with comments that I am unaware it does , you then pass over this with further questions ignoring some of the central issues.

How about a little bit of common courtesy here, eh ?

Before demanding further info from me, how about giving me some details about the leakiness of foams when I have said I am unaware that this is correct ?

I think that is reasonable, don't you ?

As regards the foil on the boards, can you quote me anything definitive ?

I have not found anything, which is a reason for my "belief" because a company with a good sales-argument will make sure it is prominent in sales-literature.

 

[holmslaw]

..

 

[ColJack]

the foil facings are for thermal reasons, reflecting the heat back into the room same as those sheets you can get to go behind the rads..

as for spock, it depends when you mean..
he ended up as a captain in the movies I believe, and an ambasador in TNG..

 

[ban-all-sheds]

You put to me that PIR, PUR absorbs water, I reply with comments that I am unaware it does , you then pass over this with further questions ignoring some of the central issues.

I believe it does, but I'll find out - I've got a few odd bits of 50mm Kingspan - I'll immerse some in water and see what happens.

Before demanding further info from me, how about giving me some details about the leakiness of foams when I have said I am unaware that this is correct ?

They definitely do lose gas, with a concomitant drop in R-value, and I believe that BS EN 13165:2008, the standard for thermal insulation products for buildings - factory made rigid polyurethane foam (PUR) products specifies that the advertised values are to be the ones that apply after X years.

Hence my comment, because if you're basing your belief that they can't allow water vapour through because they are closed cell, and if they did that would mean that the blowing gas would escape then....

But as I say, I'll give it a try. Probably not very scientific, but might tell us something.

In passing I note that on Celotex's Technical FAQs page it says

Celotex is not suitable for use in inverted roofs (protected membranes) as it must remain dry at all times.

and

Celotex can be used below the damp proof course (DPC) providing there is a clear cavity. If there is any likelihood that it will be in wet conditions, it should be protected by a damp proof membrane (DPM).

which indicates some sort of susceptibility to moisture.

As regards the foil on the boards, can you quote me anything definitive ?

Can I recess my downlighters into Celotex?

No. Downlighters should not be recessed into insulated ceilings as they penetrate the vapour control layer (VCL)

and

How to avoid condensation risks?
.
.
Condensation in buildings is controlled with a variety of methods.

• Vapour Control Layers
A vapour control layer is a material with a high resistance to the passage of water vapour. This might be a foil faced insulation board (like Celotex) or a polythene membrane.

The principle is to prevent moisture in the air from reaching the cold side of the insulation, where it could meet a cold surface and condense.

I've not looked at other makers sites, but all the PUR/PIR products are broadly the same.

I have not found anything, which is a reason for my "belief" because a company with a good sales-argument will make sure it is prominent in sales-literature.

It is prominent, and clearly spelled out, so if it was b******s wouldn't it be widely challenged, and/or wouldn't there be companies selling competing products at lower prices because they didn't have a foil layer, explaining that such a layer was actually made of snake oil?

 

[ban-all-sheds]

the foil facings are for thermal reasons, reflecting the heat back into the room same as those sheets you can get to go behind the rads..

That doesn't work unless there's an air gap on the warm side, and they sandwich a foil layer between the plasterboard and the foam in composite boards, so it can't be for that...

 

[mointainwalker]

@banal

I know that the insulating gas seeps out and that there is a proposal ( don't remember from whom) to give U values based on testing at 7 years.

I do not think, however that there is a sudden collapse of the structure and the leakage is therefore extremely slow : since water-vapour has very large molecules ( why Gore-Tex works) compared to other gases, I think it highly unlikely ( surmise here ) that this vapour could penetrate the board and its still existing cell-structure.

I looked at the Celotex site and every product viewed mentions "..a low emissivity foil-coating.." so as far as that goes, I interpret that as an insulation addition, not vapour barrier.

I didn't look up the down-lighter bit, but since all Celotex appears to be foil-coated, it would be standard marketing-practice to always refer to similar products as "foil-coated " therefore not necessarily meaning that the foil is required as a vapour-barrier but it's there anyway.

Although it is of little relevance to the discussion, a test of expanded polystyrene ( read long ago) said that after 30 days total immersion the poly had increased its mass by 0.2% absorption of water.

I suppose you could say, if in doubt buy poly ! Especially since it has no gassing problems and no change in U value.

I haven't worked it out, but since PIR/PUR is reckoned to be down at the same U values as exp poly and fibre-wool after 7 years, I think it is likely to be a poor choice of insulation from a financial stand-point.

Bit unhappy about that as when my house was re-roofed, the roofer used 100 mm T+G PUR boards which cost a bloody fortune.