Does the U value of rigid, foam-based insulation deteriorate over time?

ircoha

To set the scene for this thread

from http://www.irishbuildingindustry.ie/directory/insulation-materials/

Insulation is a passive product, once installed it works efficiently, quietly and continually, usually out of sight enclosed within a structure, a casing or under cladding. The extensive range of roof, wall and floor insulation comprises of
rigid phenolic insulation,
high performance rigid urethane insulation,
rigid extruded polystyrene insulation for specialist applications,
ultra-thin aluminium foil bubble insulation,
natural sheep wool insulation....

The main focus of this discussion is on the rigid boards and not on the ultra-thin or sheeps wool. Note the word passive.

[ obvious omissions include the relatively new wood fibre insulation materials and good old glass fibre.]

Regular readers of this forum and the other forums will be aware that there is a body of opinion out there that suggests that the insulation value of 'rigid' insulations such as

Polyisocyanurate foam [PIR ]

Phenolic Rigid Board

Rigid polyurethane [PUR]

Extruded Polystyrene (XPS)

deteriorates over time with a resultant loss of U value. {if some commentators were to be believed the products end up having no residual insulation value and that they act as cold bridges.}
Needless to say the 'Ard Ri' of this stuff would dispute this notion and also one has to be aware of the vested interests of some of the detractors of any rigid material.

The main reason for this deterioration is described in layman's terms as 'degassing' of volatile gasses that occupy the voids and are replaced by air and if this is the case, this stuff cannot be regard as passive. This degassing argument is also used as a reason for installing MVHR

The one that appears not to suffer from such criticism is
Expanded Polystyrene (EPS) as the voids seem to comprise of air, despite the fact that the base material, polystyrene beads contain pentane gas.

This would seem to suggest that EPS is a better product at the end of the day than the other foam based products.

I would welcome a discussion on this without risking a MCD type outcome.

sydthebeat

Any rep of either of the 'top 2' PU or PIR ive ever put this question to always assured me that the resultant inevitable replacement of penthane gas by air only minimally affects the performace thermal conductivity of the boards. They always maintain that this inevitable replacement is taken into account when declaring thermal conductivity values. some have stated that the factory thermal conductivity is closer to 0.02 than 0.023.

I would tend to consider that the effect of gausses law is minimal on these products as all insulation is basically trapped air anyway.

sinnerboy

The rigid foam insulation providers since 2001 ( i think ) have to declare 25 year aged values

so a kingspan/xtratherm/quinntherm / ballytherm ( named em all so no favours given ) with a declared lambda value of say 0.023 W/m K will "leave the factory floor" performing at 0.018 W/m K

tests to establish an aged declared value simulate aging by slicing the product up thinly and exposing it to high temps ( 70 degrees C ) . I can't recall how long for

the bulk of the ageing occurs ( or more accurate to say - is predicted by simulation to occur ) in the first 8 years . after that the decline in performance tails off .

I asked a cavan based manufacture about this and they insist that unless the product is cut , no gases will be exchanged . foil facings ( as well as "activating" cavities to improve their thermal emissivities ) act to prevent gas exchange

When pressed by me on the subject a not cavan based manufacturer stated that even if all gases are exhausted you would still have replaced it with air - i.e. the product will not degrade entirely - it would perform at about 0.04 ~ 0.35 - the same as fibreglass .

my 2p worth ( and i swear i have nothing personally to gain ) is that these products can't be matched in terms of performance . YET .

Those boards will be performing long after we're all pushing up daisy - that is my belief

I do expect to be challenged .

ircoha

SB: thanks for this:
Would be grateful for a link on the 2001 'agreement' if possible.

The other interesting point that arises here is that smaller sheets, say as used between roof members that are exposed to a higher temperature than on the inner layer of your (patented:) ) 50 on 50 inner wall sandwich which would be using full size sheets, and therefore the lambda value will drop off to a lower level quicker in the roof.
Dropping from 0.023 to 0.035 over time is an interesting consideration.

sinnerboy

I.S. EN 12667 :2000 ‘Thermal performance of building materials and products – Determination of thermal resistance by means of guarded hot plate and heat flow meters method – Products of high and medium thermal resistance’.

Is an agreed EU method for measuring thermal performance . IAB and BBA ( and DIN ) etc will make manufaturers test there products using this agreed method before issung the IAB BBA DIN etc cert .

Don't have a link to this - though unless you want to set up a test lab and implement your own testing ... it may make for dull reading

Mellor

This was thrown about here for a long time, I repeatedly axked for somesort of basis for this and was never entertained.

First of all insulation will will drop inporformance over time, all rigid, all fibreous insultion, and the unique stuff such as straw bale and cellouse etc.

My main gripe with the theory is that it takes the fact that when the blowning agent
migrates from the rigid board the conductivity increases. It then uses this fact to suggest that the board' performance drops to nothing. This is not true, and can be shown easily,

• The blowing agent is replaced with air (if it wasn't the performance would improve)
• Trapped is a very good insulator, it is this basis that all construction insulations work, (all rigid boads, fibreglass and similar, sheepwool etc)
• This is also illustrated by the fact that EPS (which is trapped air) maintains a reasonable performance

I think sinners estimation of 0.04 ~ 0.35 is on the negitive side. I had to estimate it, I would say that it falls to the level of EPS at best. I am basing this on the fact that EPS is trapped air, an XPS and pheonol based insulations are better from a thermal density POV.

sinnerboy

Mellor wrote: »

I think sinners estimation of 0.04 ~ 0.35 is on the negitive side. I had to estimate it, I would say that it falls to the level of EPS at best. I am basing this on the fact that EPS is trapped air, an XPS and pheonol based insulations are better from a thermal density POV.

Actually - that was a typo ( Thanks Irocah for the pm )

I meant 0.035 to 0.04 IF it even drops to this

how could it for example

- located between layers of torch on felt in warm roof

- located between conc sub floor and screed

even in a partial fill cavity wall - no extremes of temp . no significant air movement ( if well built - i know you will get thermal looping with bad workmanship ) . even here the foil facings will inhbit exchange of gases

just like the milennium bug ( remember that ) - it aint gonna happen

Mellor

Sorry, i just copied and pasted your typo, I knew you meant .035-.04

I think that if all the pethane (or similar BA) id replaced with air, then worst case scenerio, it will be 0.028, like EPS

ircoha

Thanks guys for all the input: a fair and balanced discussion all round, and not a low radon attic extension in sight:)

The discussion was probably timely given the announcement by ER to pilot some insulation projects.

http://www.boards.ie/vbulletin/showthread.php?t=2055281649

Two additional points which may add value to the rigid board end is the low emissivity of the alu foil and the foil's ability to function as a vapour 'thingy', which should make it better than 'naked' EPS.