A friend of mine has been made to install polythene under and above his insulation to a ground bearing slab and to tape all the joints between the PUR boards

The BI said that the manufacturers require this to prevent decay????

Doubling the ammount of poly seems mad to me.

spoke to celotex tech help line a few years ago about this and its a mike suggests
thier concerned about the cement screed damaging the foil face ,
on the plus side its a added layer of protection from the screeding process.
but I've found it quite common for the foil to become seperated from the foam in the high traffic areas
when doing UFH or screeding even if you make efforts to protect it with boards, planks etc .

I wonder what the lambda values like without the foil , closer to EPS I guess ?

Would it make a diference to the thermal performance of the PUR if they sandwhiched the foil in foam, about 5mm below the surface?

What difference does foil actually make to insulation? I have not seen actual U-value comparisons with and without.

I am laying non-foil insulation onto a concrete slab and then a screed containing UFH pipes on top. I was wondering about putting a layer of foil either between the insulation and the slab, or between the insulation and the screed. I was wondering which would be more effective, or indeed whether either was worth the money (50p/sqm) in terms of reduced heat loss. And now this thread raises another question - would the foil last?

The foil in foil-faced PUR board is to retain the blowing agent (which gives it better thermal performance than if the bubbles were filled with air). Any radiant barrier effect is secondary. Of course, if you're covering it in concrete, then it makes no difference and the aluminium would be destroyed by the cement anyway (or lime if you were going that route).

Paul in Montreal.

Posted By: Mike GeorgeHi Paul, I thought the foil was used to check against water vapour, rather than the blowing agent. What stops the gas from escaping at the edges? Or does it? is this the reason why some say PUR off-gasses and subsequently deteriorates?

I think it provides both functions. But yes, some blowing agent will escape from the sides, but the path is very much longer than through the surface. The foil also provides some mechanical protection as well as UV light protection (though most of the time the board is in darkness).

You can definitely smell the blowing agent when you cut the boards though :)

Paul in Montreal.

I am still monitoring the 100mm PUR I laid flat in my attic about 5yrs ago. So far no visible signs of deterioration.

It definitely smells thoughwhen you cut it. I recently had a client complain about this

I expect only the manufacturers are in a position to monitor and know that - and they're probably not saying

So presumably the gas would be replaced by air? And if so there would be no visible signs of deterioration it terms of thickness?

Also not much worse performance given the low conductivity of air?

The usual blowing agent for foil faced boards these days is pentane. I'm not sure how the diffusion works because I'm not sure if the foam itself is open cell (ala icynene - which I read somewhere recently is made from castor oil) or is closed cell (like extruded polystyrene). Even if the gas does escape, the foil still functions as a vapour control layer.

Paul in Montreal.

Paul

I know that kingspan is 90% closed cell. I would guess the other similar products on the market have a similar makeup.

Timber

Posted By: julesThank you. I won't be bothering with the foil then.

Whilst we're on the subject of lifetime performance of Kingspan and the like, do these things shrink at all over time? I am sure I read that somewhere, but was a bit sceptical.

ECOTherm were explicitly saying they don't shrink (among other things) and Kingspan were pretty strong on pushing one the "advantages" of PUR/PIR was that the performance does not degrade below specification over time.

The manufacturers, at least, are claiming that there is no shrinkage.

Posted By: Mike Georgethe gas would be replaced by air? ... not much worse performance given the low conductivity of air?

No, on the contrary, considerably worse performance than you'd been led to believe and paid lots extra for.

Posted By: fostertomIcynene, which is water-blown soft PUR foam, with claimed lamda of 0.039, whereas exotic-blown 'normal' rigid PURs claim about 0.029. I wondered whether the Icynene's 0.039 is what the exotics would eventually fall to.

Posted By: jamesingramheard someone ... claiming once the gas has gone the PUR lambda values is equivilent to EPS

Posted By: tonysmall bits i would say loose all the gas within a year full sheets a few years -- guessing

Posted By: Mike GeorgeI expect only the manufacturers are in a position to monitor and know that - and they're probably not saying

Well, we need to know - someone must know. Sounds like yet another insulation industry racket.

Posted By: fostertom

Posted By: MarkBennettECOTherm say: "They will not rot, shrink or absorb moisture, or decay as some fibre board or organic insulation materials may, and so they will deliver design insulation values throughout the full life of the building."

They omit to say whether they will lose blowing agent, so 'they will deliver design insulation values throughout the full life of the building' is possibly a candidate for an advertising standards complaint.

Kingspan use similar wording, and while they admit candidly that the performance of the material degrades over the first few years, they state that the quoted performance is after 7 years, and is essentially the same as the ultimate performance. The initial performce for the first 7 years will be better than they quote. As such, it seems that they are delivering "design insulation values", i.e. the values quoted in the specification, thoughout the lifetime of the material. See sheet 31 of: http://www.insulation.kingspan.com/uk/ifs_full_version.pdf

There is, apparently a European standard (EN 13165) which specifies how the insulation values for PUR/PIR insulants should be measured. I woudl be surprised if Kingspan, Celotex and ECOTherm didn't quote performance according to these standards.

If you have seen any evidence to the contrary regarding the ageing of PUR/PUR insulants then I'd be very interested in reviewing it.

Posted By: fostertom

Posted By: Mike Georgethe gas would be replaced by air? ... not much worse performance given the low conductivity of air?

No, on the contrary, considerably worse performance than you'd been led to believe and paid lots extra for

Something must occupy the space previously occupied by the blowing agent. If not air then what?