Green Building Forum - How airtight is EWI when done right? Tue, 19 Dec 2023 05:52:08 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255334#Comment_255334 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255334#Comment_255334 Tue, 07 Mar 2017 13:34:23 +0000 ringi
What if the EPS was put on in the normal way without sealing with expanding foam, but the render was still done to a reasonable standard?]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255336#Comment_255336 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255336#Comment_255336 Tue, 07 Mar 2017 13:42:01 +0000 MikC How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255337#Comment_255337 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255337#Comment_255337 Tue, 07 Mar 2017 15:10:46 +0000 djh How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255340#Comment_255340 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255340#Comment_255340 Tue, 07 Mar 2017 19:30:09 +0000 gravelld
But I guess most EWI "systems" have a modern render which, apparently (!), don't crack.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255341#Comment_255341 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255341#Comment_255341 Tue, 07 Mar 2017 20:19:16 +0000 fostertom How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255342#Comment_255342 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255342#Comment_255342 Tue, 07 Mar 2017 21:45:12 +0000 djh Posted By: fostertomNot having a lump to hand to suck at, is EPS itself airtight, never mind the joints?
I don't believe so, no. But nobody is supposing that it is AFAICT?]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255344#Comment_255344 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255344#Comment_255344 Tue, 07 Mar 2017 21:49:35 +0000 djh Posted By: gravelldDepends on the render too, because we're concerned about long term air tightness, not just passing a test.

But I guess most EWI "systems" have a modern render which, apparently (!), don't crack.
If the render cracks, you simply repair it. But external render is susceptible to far more influences that are likely to crack it than is internal plaster, which is one factor in the preference for internal airtightness barriers. But again, it is the connections that are likely to be most problematic.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255353#Comment_255353 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255353#Comment_255353 Wed, 08 Mar 2017 09:14:59 +0000 gravelld
Good point as to another reason why internal plaster is preferred.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255354#Comment_255354 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255354#Comment_255354 Wed, 08 Mar 2017 09:17:31 +0000 gravelld https://www.aecb.net/forum/index.php?topic=2630.msg10700#msg10700]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255357#Comment_255357 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255357#Comment_255357 Wed, 08 Mar 2017 10:42:31 +0000 fostertom Posted By: gravelldPaul Jennings on this subjectA gd link, what with other comments (not properly answered there)!]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255359#Comment_255359 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255359#Comment_255359 Wed, 08 Mar 2017 10:54:28 +0000 fostertom Posted By: ringiassume that ... the renter is put on with careYes, tenant behaviour can outwit best intentions!

Posted By: djh
Not having a lump to hand to suck at, is EPS itself airtight, never mind the joints?

I don't believe so, no. But nobody is supposing that it is AFAICT?
Yes, I think they are supposing that.
Ringi's OP Q is in two parts - the second part is about just the finish render alone, as contributor to airtightness.
The first part is also about the contribution of the EPS - and improving that by 'all the gaps between EPS sheets are sealed with expanding foam'.
I'm suggesting (suddenly realising?) that sealing the gaps (my longtime insistence) may in fact be futile if the EPS itself is air permeable.

My priority, in sealing the gaps, wasn't to do with airtightness as such - I assume the EWI doesn't contribute to that reliably - but in preventing inside-to-outside thermal bypass convection through the joint gaps, even if they're only fag-paper width.
Now maybe realising that the entire EPS face is one big convection path from inside to outside!]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255362#Comment_255362 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255362#Comment_255362 Wed, 08 Mar 2017 11:15:04 +0000 MarkyP How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255363#Comment_255363 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255363#Comment_255363 Wed, 08 Mar 2017 11:55:24 +0000 DarylP ]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255365#Comment_255365 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255365#Comment_255365 Wed, 08 Mar 2017 12:19:49 +0000 djh Posted By: fostertomMy priority, in sealing the gaps, wasn't to do with airtightness as such - I assume the EWI doesn't contribute to that reliably - but in preventing inside-to-outside thermal bypass convection through the joint gaps, even if they're only fag-paper width.
Now maybe realising that the entire EPS face is one big convection path from inside to outside!
Things don't have to be airtight to resist convection. Think about wool insulation, of all types. As another example, there is reason to suppose that there is some convection in straw bales, but it's not much (different k-values for different straw orientation in the bales).

FWIW, I did just put my mouth up to a piece of EPS and blow. It's hard to be completely sure, but I think some air was passing through the EPS. In the interests of science, I suggest that somebody repeats the experiment!]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255366#Comment_255366 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255366#Comment_255366 Wed, 08 Mar 2017 12:30:27 +0000 fostertom
Posted By: djhThings don't have to be airtight to resist convection
Why haven't I thought this through before? So then why have I been insisting on filling the gaps between EPS blocks, even fag-paper thickness, to prevent inside-to-outside convection - when the EPS itself has plenty of such gaps - albeit convoluted, not straight-through? What does the Brains Trust think?]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255367#Comment_255367 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255367#Comment_255367 Wed, 08 Mar 2017 12:37:06 +0000 fostertom Posted By: MarkyPassuming the render creates an air tight skin, is convection possible through pore spaces in EPS and a fag paper gap between boards?Convection's not same as non-return through-passage of air.

Convection can occur even when one or both faces of the sample (e.g. EPS block) are airtight, if one face is warmer than the other.
Buoyancy causes denser colder air to gravitate to displace lighter warmer air, in a circular motion returning on itself.
That can obviously happen in a vertical-plane inside-to-outside joint, perhaps less so in a horizontal one - and we're suggesting here that it can also happen in the intersticies of a EPS block.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255368#Comment_255368 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255368#Comment_255368 Wed, 08 Mar 2017 13:47:14 +0000 Ed Davies Posted By: djhFWIW, I did just put my mouth up to a piece of EPS and blow. It's hard to be completely sure, but I think some air was passing through the EPS. In the interests of science, I suggest that somebody repeats the experiment!Tried with vacuum cleaner sucked up against a block of EPS with a pressure sensor in the block, wrapped in plastic sheet. The pressure sensor is quite capable of measuring the pressure increase, at about the level of its own noise, when I bring it downstairs yet didn't see any decrease as set up here. Still, there wasn't an obvious decrease when I put the vacuum cleaner nozzle right in the box either, which did surprise me. OK, the plastic sheet was hardly sealed round the edges but I'd still have expected some drop in pressure. It's quite a powerful vacuum and I suspect it sucks more than Tom or Dave.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255372#Comment_255372 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255372#Comment_255372 Wed, 08 Mar 2017 14:30:12 +0000 Peter_in_Hungary With EWI if there are gaps behind the EPS and a path top to bottom or gaps in the EPS wall then convection current can be set up from the bottom to the outside somewhere. (or from a lower gap in the EPS wall to a higher gap). But in any event IMO there won't be sufficient space within the EPS for convection to work as a closed volume, an exit for the warmer air as well as an input will be needed.
So IMO any breathability of EPS should not be a concern for heat loss but any gaps that allow through flow of air would be a concern. The normal thin coat render with the glass mesh embedded I would have though would be sufficiently robust and flexible not to crack with normal conditions, and even then a crack would have to coincide with an air passage in the underlying EPS. The thin coat render is surprisingly (to me anyway) flexible. There was a problem locally last year where several houses had the EWI render damaged by egg sized hail stones where the hail knocked off bits of render where they struck. The mesh remained intact and the biggest problem with the repair was matching the colour of the top coat (batch number differences) The same hail storm destroyed more roofs than damaged EWI.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255374#Comment_255374 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255374#Comment_255374 Wed, 08 Mar 2017 14:43:20 +0000 djh Posted By: Ed DaviesI suspect it sucks more than Tom or Dave.
I resemble that remark! And I'm not going to get into discussions of who sucks and who blows :devil:

Your EPS, Ed, looks like packaging, which I think is typically a finer (less expanded?) variant than EPS70. I don't know whether that would make any difference.

Tom, convection isn't the only force that drives air movement. Air pressure changes, such as wind, also drive movement, either by forcing air all the way through barriers or by alternately compressing and expanding the air within a cavity.

Not leaving cavities in construction helps by reducing the volume of air that can be moved by such forces, providing less opportunity for heat and moisture movement, although there have to be continuous barriers as well.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255377#Comment_255377 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255377#Comment_255377 Wed, 08 Mar 2017 15:06:19 +0000 fostertom Posted By: Ed Davieswith a pressure sensor in the block, wrapped in plastic sheetHow dya mean 'in the block' - do you mean in the bag? Why should air in the bag show any pressure change (as air is sucked from the bag?) when the bag is extremely free to deflate to equilibriate pressures?

Does this sample of packaging-grade EPS actually have a sealed melted or tight from-the-mould surface rather than cut as building-grade EPS is?

Posted By: Ed DaviesIt's quite a powerful vacuum and I suspect it sucks more than Tom or Dave
In volume no doubt but in static vacuum possibly less. My muscular mouth is a very effective vacuum chamber! - far stronger than my lungs in blowing mode.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255379#Comment_255379 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255379#Comment_255379 Wed, 08 Mar 2017 15:20:44 +0000 skyewright Posted By: fostertomMy muscular mouth is a very effective vacuum chamber! - far stronger than my lungs in blowing mode.
Muscular as it might be, I rather doubt it's a match for a decent vacuum cleaner. Our 'Henry' wants to pick up carpets & rugs even on the half power 'eco' setting...]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255380#Comment_255380 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255380#Comment_255380 Wed, 08 Mar 2017 15:20:57 +0000 MarkyP Posted By: fostertomConvection's not same as non-return through-passage of air.

Convection can occur even when one or both faces of the sample (e.g. EPS block) are airtight, if one face is warmer than the other.
Buoyancy causes denser colder air to gravitate to displace lighter warmer air, in a circular motion returning on itself.
That can obviously happen in a vertical-plane inside-to-outside joint, perhaps less so in a horizontal one - and we're suggesting here that it can also happen in the intersticies of a EPS block.

I realise convection isn't just a draught moving through the EPS. But my understanding of convection is that the air pocket size is highly signifnicant in the potential for heat to move through an air space. Like PiH said. So does convection actually happen at a level that is even remotely signficant in tiny spaces? Can a convection path really establish in a highly irrelgular, sub millimetre air pathway across an EPS board?

And here's another thought - how are r-values calculated for EPS? How does the test avoid this convection? Or is it unavoidable and therefore the quoted R-value includes this tiddly bit of convection?]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255382#Comment_255382 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255382#Comment_255382 Wed, 08 Mar 2017 15:43:46 +0000 fostertom Posted By: MarkyPhow are r-values calculated for EPS? How does the test avoid this convection? Or is it unavoidable and therefore the quoted R-value includes this tiddly bit of convection?Good question - and throw in highly significant internal radiation across gaps.

R or lamda values are indeed a composite - certainly not just conduction - and as such contain many assumptions, the most important fallacy being the 'steady state' one, which simply doesn't exist in natural heat-transfer situations (or even in the test hot-box) any more than it does in weather patterns.

Once that real-world transience (incl high frequency micro-oscillations) is admitted, the real insulativeness (outside the hot-box) of conventional insulations is worse than advertised and that of anything using radiant-barrier (e.g. multifoil) or radiant-absorber (e.g. aerogel, graphited EPS) techniques in better, in reality.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255390#Comment_255390 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255390#Comment_255390 Wed, 08 Mar 2017 18:04:29 +0000 djh Posted By: MarkyPCan a convection path really establish in a highly irrelgular, sub millimetre air pathway across an EPS board?
Not by itself no. The boundary layer drag would prevent it. But if a temperature difference establishes different pressures on either end of a narrow channel, then the air might be forced through it if there is sufficient pressure. So it might complete a convection circuit.

The lambda values of insulation are determined using a guarded hot plate. There's a brief description at https://www.ibp.fraunhofer.de/content/dam/ibp/en/documents/Fl-174-01-Flyer-Plattanapparat-Mai2011-Etcm1021-92195.pdf
There's an interesting article at https://en.wikipedia.org/wiki/Thermal_conductivity_measurement that shows alternate ways that could be used if the building world could be dragged screaming into the twentieth (sic) century. [No disrespect intended to those who design the guarded hot plates]]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255400#Comment_255400 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255400#Comment_255400 Wed, 08 Mar 2017 19:02:20 +0000 fostertom That would mean no need to squirty-foam fill all EWI EPS joints (not an accepted industry thing anyway, just perfection (prob instigated by me) on GBF), just bigger ones (how big)?

To be clear, this is a question about recirculating convection, separate from any consideration of straight-through air passage.

Convection could happen even with good airtightness; straight-through only with poor airtightness.

But to preclude straight-through air passage through the EWI, the airtightness doesn't have to be in the EWI - it can be inboard, outboard or as I prefer it, in the OSB tea cosy in the middle of the sandwich.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255402#Comment_255402 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255402#Comment_255402 Wed, 08 Mar 2017 19:14:34 +0000 Peter_in_Hungary
Of course straight through convection is another matter which is why I won't accept any 'dot and dab' fixing of EPS but insist on a continuous line top and bottom of the EPS sheets as a minimum.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255407#Comment_255407 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255407#Comment_255407 Wed, 08 Mar 2017 19:57:47 +0000 gravelld Posted By: fostertomSo PiH and djh, are we saying that a) narrow joints between EWI blocks and b) the intersticies of EPS are small enought to guarantee (recirculating) convection negligible?
That would mean no need to squirty-foam fill all EWI EPS joints (not an accepted industry thing anyway, just perfection (prob instigated by me) on GBF), just bigger ones (how big)?

To be clear, this is a question about recirculating convection, separate from any consideration of straight-through air passage.

Convection could happen even with good airtightness; straight-through only with poor airtightness.

But to preclude straight-through air passage through the EWI, the airtightness doesn't have to be in the EWI - it can be inboard, outboard or as I prefer it, in the OSB tea cosy in the middle of the sandwich.[I might have lost track of this thread] Agreed, but the OP is about how airtight is EWI, as a result I think straight-through air passage is important, because other air barriers can be breached, e.g. outbound render, as I suggested above, regardless of whether the render can be fixed or not.

There's no problem seen in redundancy (of air tightness) is there? It's a common strategy in lots of industries.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255408#Comment_255408 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255408#Comment_255408 Wed, 08 Mar 2017 20:00:51 +0000 fostertom Posted By: Peter_in_HungaryIf you take the 2G /3G limits of spacingAh but that's a trade-off between better insulation (more thickness of hopefully still air) and less convection (less thickness). I'd guess there's considerable convection at those pane spacings but their effect is out-voted by the extra thickness of insulative (semi-still) air. I'm sure it's not 'no convection' at those pane spacings.

That trade-off doesn't apply within EWI, when any convection at all is an uncompensated negative.

Posted By: Peter_in_Hungarystraight through convection
For clarity, let's not call that convection - I've been saying 'straight-through passage of air' - any better idea?]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255412#Comment_255412 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255412#Comment_255412 Wed, 08 Mar 2017 20:34:23 +0000 Peter_in_Hungary Posted By: fostertom
Posted By: Peter_in_HungaryIf you take the 2G /3G limits of spacing
Ah but that's a trade-off between better insulation (more thickness of hopefully still air) and less convection (less thickness). I'd guess there's considerable convection at those pane spacings but their effect is out-voted by the extra thickness of insulative (semi-still) air. I'm sure it's not 'no convection' at those pane spacings.
That trade-off doesn't apply within EWI, when any convection at all is an uncompensated negative.

As maybe but you are not going to get anywhere near 19mm gaps in EWI (I hope) maybe 8 - 10 mm between the wall and the EPS and single digit mm between the EPS sheets, and then you will have rough uneven surfaces at the wall which will inhibit convection.

Posted By: fostertom
Posted By: Peter_in_Hungarystraight through convection
For clarity, let's not call that convection - I've been saying 'straight-through passage of air' - any better idea?

I don't mind what it is called - but it is heat loss using air as the transport medium and driven by the (greater) buoyancy of the higher temperature air.]]> How airtight is EWI when done right? http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255418#Comment_255418 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255418#Comment_255418 Wed, 08 Mar 2017 21:52:46 +0000 ringi
We could do with someone with the correct kit building small bad quality block or brick room and seeing how much better the air tightness is after the EPS is added, then again after it is foamed, then after the render is put on.]]>