EWI not enough space at one point.. how to handle?

[^woody^]

Yes. I appreciate that but there is also the element of internal production of vapour along with any moisture contained within the wall at time of installatio
My other concern with PIR is the way it degrades and brakes down over time.

No and no again.

 

[champagnecharly]

Yes. I appreciate that but there is also the element of internal production of vapour along with any moisture contained within the wall at time of installatio
My other concern with PIR is the way it degrades and brakes down over time.

No and no again.

Sorry, please explain.. Are you saying no vapour is created internally? And that PIR does not brake down?

 

[^woody^]

The vapour created internally is managed by the structure and natural air movement, and you don't need to consider it in this context..

The insulation board will last the life of the building and is also not a consideration.

 

[freddiemercurystwin]

It is well known that PIR's used to lose their gas, what is still undetermined is whether the manufacturers have really cured the problem or are just saying they have.

 

[champagnecharly]

The vapour created internally is managed by the structure and natural air movement, and you don't need to consider it in this context..

understood well sort of.. When you say "managed by the structure", if the struture itself cannot breathe externally how can it manage it? It would absorb from the inside and only release when ambient humidity dropped but again only to the inside and the same through air movement hence the reason for trickle vents.
But with airtightness as good as possible that would in turn reduce the airflow. so what then? would it not be the brickwork & plaster/lime that absorbs more and more.

The insulation board will last the life of the building and is also not a consideration.

I've seen several discussions in green forums to the contrary.
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=7254
that is why my concern on PIR on Solid wall. From what i read is if moisture is allowed in contact with the PIR due to failing of membrane or similar the PIR will degrade. Is it safe to rule out that possibility?

Sorry to question you.. I only do so to understand better not to challenge

 

[^woody^]

Water vapour from within a house does not go through the wall. It goes as far as the plaster, maybe a bit into the wall, and then it evaporates back out into the room air. There is not enough pressure to push condensed air moisture any further. Other moisture is held within the masonry in a state of equilibrium - controlled (or managed) by the structure and ambient air movement.

Insulation board will only break down when in conditions that attack the material structure - UV or a chemical for instance. Built into a wall, the material lasts as long as the building.

 

[champagnecharly]

Water vapour from within a house does not go through the wall. It goes as far as the plaster, maybe a bit into the wall, and then it evaporates back out into the room air. There is not enough pressure to push condensed air moisture any further. Other moisture is held within the masonry in a state of equilibrium - controlled (or managed) by the structure and ambient air movement.

Insulation board will only break down when in conditions that attack the material structure - UV or a chemical for instance. Built into a wall, the material lasts as long as the building.

Thank you! 1 further qu.. sorry.. You mention not sufficient pressure to.. but what about capillary action of the damp within plaster/wall is that not possible or is it a question that there is not sufficient moisture for that to occur to such a degree?

 

[^woody^]

There is not enough moisture from the air, or pressure, for it to be drawn into the wall by capillary action.

By the time the limited moisture is being drawn into the plaster by capillary action or diffusion, the warm air and air movement is trying to pull it back out for it to evaporate back into the air. This is a constant cycle.

 

[freddiemercurystwin]

Insulation board will only break down when in conditions that attack the material structure - UV or a chemical for instance. Built into a wall, the material lasts as long as the building.

The jury is still out on that one, I know so because the head of technical at Kingspan effectively told me so. In a few years, actual real time-dependent tests will have been carried out, not the speeded up lab tests that are currently used to claim it doesn't lose any gas at present.

 

[champagnecharly]

Ok.. From what i've read combined with my possibly silly reasons for use of fibre boards.. Would it be sufficent to use XPS where I am short of depth and 130mm mineral fibre board the remainder?

 

[freddiemercurystwin]

XPS or PIR will be fine, the PIR debate will roll on for a while yet, in theory it's still the best we have and if it turns out PIR is still losing its gas, it ends up the same as XPS anyway.

 

[^woody^]

What is this gas in the insulation that you speak of, FMT?

Charly, xps will be roughly twice as thick as a PIR/PUR product for the same u-value.

 

[champagnecharly]

What is this gas in the insulation that you speak of, FMT?

Charly, xps will be roughly twice as thick as a PIR/PUR product for the same u-value.

Yes and given what freddy says there is little point to go with XPS if the degraded U value is that of XPS.

Thanks guys!

 

[freddiemercurystwin]

What is this gas in the insulation that you speak of, FMT?

Charly, xps will be roughly twice as thick as a PIR/PUR product for the same u-value.

Dunno, I'm not a chemist! At the time of purchase XPS does need to be twice as thick to achieve the same the same heat retention. But after 5 or 25 years later (if) its lost its some/all of its gas its no longer such a good insulator. I have no agenda to steer the world away from PIR, I specify it on a daily basis but the OP pointed out a concern to which there is some truth.

 

[champagnecharly]

Seems that the gasses used are changeable with older boards using cfc gasess as the blowing agent. then there was a move to hcfc and from their to Pentane and HFC.
More information here.
http://www.epic.uk.com/assets/epic_identification_and_disposal.pdf


If 97% of the volume of the foam is trapped gas. The loss of the same can reduce the performance considerably and seemingly more than the difference between XPS and PIR? OR was your point that degraded PIR was equivelent to new XPS based on researched figures?