Green Building Forum - How airtight is EWI when done right? Fri, 17 Jul 2026 22:28:40 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255420#Comment_255420 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255420#Comment_255420 Wed, 08 Mar 2017 22:07:15 +0000 fostertom Posted By: ringiI was thinking that if the foam gun is pushed ALL the way to the back of each joint between EPS sheets then the foam would seal round each sheet to the wall, so stop air movements behind the sheets of EPS.Exactly - and all the fixing cement kept well away from block edges so no danger of it squishing into the joint.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255421#Comment_255421 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255421#Comment_255421 Wed, 08 Mar 2017 22:13:12 +0000 fostertom Posted By: Peter_in_Hungarydriven by the (greater) buoyancy of the higher temperature air [I'd add, within the wall sandwich]then let's call it convection.
But straight-through air passage is not that - it's driven by internal stack effect (which OK is buoyancy but in a different way) - and crosswise wind pressure (which isn't) - let's call that something else, for clarity. Well I will, anyway.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255424#Comment_255424 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255424#Comment_255424 Wed, 08 Mar 2017 22:32:30 +0000 Ed Davies Posted By: fostertomand crosswise wind pressureWhat do you think drives wind, then? Convection works on quite a lot of different scales.

Actually, I think that in the convection/conduction/radiation sense convection is any heat transfer by movement of a fluid though, yes, often it means movement driven by the increased buoyancy of a fluid as it's heated or cooled.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255426#Comment_255426 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255426#Comment_255426 Wed, 08 Mar 2017 22:40:14 +0000 Ed Davies Posted By: djhYour 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.Yes, it's packaging EPS. I have to admit I haven't seen insulation EPS up close (from less than a few metres away) so I don't know how much different it is: if my experiment had been at all conclusive that'd have been the next question.

Posted By: fostertomHow 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?
Yes, the block originally fitted round the end of a computer or something and the pressure sensor was inside that, surrounded by the plastic. Bit difficult to see in the photo as it's white on white but it's on the centre strut between the two holes in the EPS. I expected the bag to give at least some resistance to any inflow of air so to see some pressure drop if air was being sucked through the EPS.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255428#Comment_255428 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255428#Comment_255428 Wed, 08 Mar 2017 23:52:56 +0000 gyrogear Posted By: fostertomstraight-through air passage

how about "air-transparency" or simply "air leakage" ?

=========
Also, on a different note, per the refrenced link, "I have recently been air leakage testing several houses that have been externally insulated for a local council. I'm afraid that 100mm of external EPS insulation has a negligible effect upon the airtightness of a property."

OH DEAR ! This came as a shock to me, as I was rather hoping I'd have pretty good airtightness...

(However, I suspect that the quote refers to a renovation context...).

So how about EWI applied from new ? Would anybody be prepared to hazard a guess for me :shocked:

(for my present house, 1983) (I was not there at the time !)

We have only *50* millimeters of EPS.
Regarding external covering, it is *extremely tough* and difficult to decide what material it is - it looks like "cement board", perhaps 4 mm thick, covered with a "stippled facade paint".

Regarding the blockwork, the quality of the joints looks amazingly good (to my untrained eye) - even in the Crawlspace and Garage...

Our internal walls (two gables + North facade) are all uninsulated and have about a half-inch of plaster (beige-ish) covered with a plasticy stippled paint. The south facade wall (corresponding to back of slate cladded section) seems to be simply bare blockwork, with heavy paint.

(our walk-in basement walls are lined with plasterboard - I still have to do some trial holes to see what insulation is behind there...).

I tested the North wall plaster - it looks to be about a half-inch with - admittedly - some "light" cracking at the roof-wall junction... (which I will be addressing soon as (anathema...) I intend to add some limited IWI...).

I hope I have stayed on-subject re "how airtight is EWI" ?

Cheers,

gg]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255436#Comment_255436 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255436#Comment_255436 Thu, 09 Mar 2017 00:33:32 +0000 djh Posted By: gravelldThere's no problem seen in redundancy (of air tightness) is there
No but neither is there any value in conventional thinking. There's no way to test multiple layers and its very easy to make mistakes by sloppy thinking or sloppy workmanship. Having said that, for my small bits of timber-framed wall and for my roof, I have a membrane backed up by warmcel, which may give me some free reliability but nobody will ever know.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255441#Comment_255441 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255441#Comment_255441 Thu, 09 Mar 2017 01:17:38 +0000 ringi Posted By: fostertom
I was thinking that if the foam gun is pushed ALL the way to the back of each joint between EPS sheets then the foam would seal round each sheet to the wall, so stop air movements behind the sheets of EPS.
Exactly - and all the fixing cement kept well away from block edges so no danger of it squishing into the joint.

Why not use fixing foam to glue the EPS to the brickwork?]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255444#Comment_255444 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255444#Comment_255444 Thu, 09 Mar 2017 08:37:52 +0000 Peter_in_Hungary Posted By: gyrogearAlso, on a different note, per the refrenced link, "I have recently been air leakage testing several houses that have been externally insulated for a local council. I'm afraid that 100mm of external EPS insulation has a negligible effect upon the airtightness of a property."

Unless the air leak test was done before the application of the EWI and again afterwards - with nothing else done at the same time then it is impossible to attribute any change as being due to the EWI. Unless new tests are done after every individual remedial action you will never know what action made the (greatest) difference.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255451#Comment_255451 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255451#Comment_255451 Thu, 09 Mar 2017 09:55:38 +0000 djh Posted By: Peter_in_HungaryUnless new tests are done after every individual remedial action you will never know what action made the (greatest) difference.
Indeed, and if I was doing a renovation, I'd be very tempted to build myself an airtightness testing fan to allow me to do those repeated tests.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255457#Comment_255457 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255457#Comment_255457 Thu, 09 Mar 2017 12:08:04 +0000 fostertom Posted By: djhbuild myself an airtightness testing fanYeah! anyone know of a set of instructions/sources etc?]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255460#Comment_255460 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255460#Comment_255460 Thu, 09 Mar 2017 12:11:47 +0000 tony How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255461#Comment_255461 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255461#Comment_255461 Thu, 09 Mar 2017 12:17:45 +0000 gyrogear Posted By: Peter_in_HungaryUnless the air leak test was done before the application of the EWI and again afterwards - with nothing else done at the same time then it is impossible to attribute any change as being due to the EWI. Unless new tests are done after every individual remedial action you will never know what action made the (greatest) difference.

Very good point, PIH, thanks !

gg]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255463#Comment_255463 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255463#Comment_255463 Thu, 09 Mar 2017 12:53:20 +0000 fostertom Posted By: ringiWhy not use fixing foam to glue the EPS to the brickwork?You might need an awful lot of it, and you'd be on your own as far as suitability/durability etc. The system suppliers provide cementitious stuff and you use tons of it.

Wouldn't large dobs of even fixing foam still do enough expanding to push blocks out of line? That's certainly a tendency when it's used in smaller dobs for fixing EPS to dead-flat e.g. OSB (is recommended for that situation). Better there to use a 2 x 30% coverage 'spider web' of spray contact adhesive, for instant grab.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255464#Comment_255464 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255464#Comment_255464 Thu, 09 Mar 2017 12:57:59 +0000 gravelld Posted By: fostertom
Posted By: djhbuild myself an airtightness testing fan
Yeah! anyone know of a set of instructions/sources etc?Often repeated and discussed on BuildHub.]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255465#Comment_255465 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255465#Comment_255465 Thu, 09 Mar 2017 12:58:55 +0000 gravelld Posted By: Peter_in_Hungary
Unless the air leak test was done before the application of the EWI and again afterwards - with nothing else done at the same time then it is impossible to attribute any change as being due to the EWI. Unless new tests are done after every individual remedial action you will never know what action made the (greatest) difference.Pretty sure this is what Paul Jennings would suggest and *probably* has experience of :wink:]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255467#Comment_255467 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255467#Comment_255467 Thu, 09 Mar 2017 13:01:51 +0000 gravelld Posted By: djh
Posted By: gravelldThere's no problem seen in redundancy (of air tightness) is there

No but neither is there any value in conventional thinking. There's no way to test multiple layers and its very easy to make mistakes by sloppy thinking or sloppy workmanship. Having said that, for my small bits of timber-framed wall and for my roof, I have a membrane backed up by warmcel, which may give me some free reliability but nobody will ever know.Sorry, so I understand, where's the conventional thinking here? I thought convention was not to bother with any of this, throw some blocks up and collect the ECO grant. :wink:

Of course, all layers would require assurance of quality. It's no good having redundant computers on a 747 if they are running Windows.

I also agree that until it's measurable it's also very hard to trust either way, but sometimes some things aren't measurable, because of any number of constraints and you do have to begin trusting in best practice even without SMART outcomes. Although definitely measure if you can and the results are reliable!]]> How airtight is EWI when done right? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255487#Comment_255487 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14960&Focus=255487#Comment_255487 Thu, 09 Mar 2017 20:57:48 +0000 djh Posted By: gravelld
Posted By: fostertom
Posted By: djhbuild myself an airtightness testing fan
Yeah! anyone know of a set of instructions/sources etc?
Often repeated and discussed on BuildHub.
and at least twice here]]>