Green Building Forum - Article challenging the benefit of breathability Tue, 19 Dec 2023 05:55:29 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62520#Comment_62520 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62520#Comment_62520 Tue, 22 Sep 2009 18:02:57 +0100 Mike George Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62530#Comment_62530 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62530#Comment_62530 Tue, 22 Sep 2009 18:45:08 +0100 tony Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62533#Comment_62533 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62533#Comment_62533 Tue, 22 Sep 2009 19:26:26 +0100 Mike George 2. Agree, but the important point for me is the circumstances under which moisture passing through fabric can cause damage. I have seen it suggested that some insulations exacerbate interstitial condensation problems, even that some cause it. This I think is wrong, as it is not any particular insulation which can cause problems, it is only when they are used or installed incorrectly, ie in a construction method not tested and approved by the manufacturers This point is well made in the article I think
3. Agree completely, but some products are promoted as having additional benefits which are, shall we say, unproven. I've not read the full Cambridge study yet but will be requesting a copy to see more detail of the conclusions.
4. Again, I agree that walls 'breathe' in the sense suggested, but would suggest that this is irrelevant, at least in new construction. It' the choice of components which make up the whole building element which is important.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62534#Comment_62534 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62534#Comment_62534 Tue, 22 Sep 2009 19:41:54 +0100 CWatters Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62544#Comment_62544 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62544#Comment_62544 Tue, 22 Sep 2009 21:43:35 +0100 fostertom http://markbrinkley.blogspot.com/search/label/Ventilation especially 3.7.07 and 6.7.07. "there is about 100 times more bound water in the structure and furnishings in a house than there will ever be free floating water vapour in the air" "a detached house ... could be holding as much as 10 tonnes of bound water ... 10m3 in volume, about the size of a small bedroom" "All this bound-water doesn’t have to stay bound. When conditions dictate otherwise, it can either absorb more water or it can release water via evaporation. This does rather depend on the surfaces surrounding the materials".

It's the ins and outs of the water already in the structure that causes trouble - is it better to let it come and go unobstructed, or trap it in various cells and compartments, or worse still, force all the traffic to pass through the few permeable bits e.g. through the studs and rafters because the Cellotex in between them is impermeable? Plenty of evidence that that situation causes saturation of the timber, even if the overall humidity levels are nothing special.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62548#Comment_62548 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62548#Comment_62548 Tue, 22 Sep 2009 22:03:49 +0100 Mike George Posted By: fostertomPlenty of evidence that that situation causes saturation of the timber, even if the overall humidity levels are nothing special.

Thanks Tom, but can you post a link to some evidence of where Timber has been saturated [in a scenario where manufacturers guidance has been followed such as via a BBA Certificate]]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62552#Comment_62552 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62552#Comment_62552 Tue, 22 Sep 2009 22:32:44 +0100 fostertom Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62557#Comment_62557 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62557#Comment_62557 Tue, 22 Sep 2009 22:55:34 +0100 biffvernon Posted By: CWattersI thought trickle vents provided as much as 3 air changes an hour How much air passes through one of those infernal gimmicks depends on which way the wind is blowing. Or at least on the pressure differential across the vent. And, of course, whether someone has opened or closed the little flap. Someone will, at some time, have either opened or closed it, and then probably forgotton about it. At any given moment in time there maybe a 0.5 probability that any given trickle vent will be open, or closed. Or maybe not.]]> Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62558#Comment_62558 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62558#Comment_62558 Tue, 22 Sep 2009 23:05:35 +0100 tony Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62559#Comment_62559 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62559#Comment_62559 Tue, 22 Sep 2009 23:09:14 +0100 jamesingram open or closed , not much trickling going on there!]]> Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62560#Comment_62560 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62560#Comment_62560 Tue, 22 Sep 2009 23:47:44 +0100 fostertom
It's an old trick - set up a ridiculous proposition then knock it down. Don Quixote. The study proves what we all know - internal water vapour generation has to be removed by ventilation, or bulk air exchange as they call it, whether deliberately or by fabric leakage. No-one expects 'breathing' construction to achieve that, without ventilation. Well, there's a little speculation that it might help, indeed possibly even selectively diffuse-out pollutants - but that's not what breathability is meant for. So a research project to prove that bulk air exchange accounts for 95% of humidity reduction by water-vapour removal, and that 'moisture transfer by diffusion is an irrelevance' is not news. That's as far as the research project went - the second half of the article is just the author's 'common-sense' aka sales chat.

The whole risk of 'moisture may become trapped when some insulation products are fixed externally to a wall' is covered by the pious hope that 'it should generally be expected that the construction material in question is given time to dry out ...' The true purpose of breatheable construction, to allow the free passage, in and out through the fabric, in a fail-safe way, of the large seasonal flows of atmospheric (and residual constructional) water vapour, which dwarf the internal production of water-vapour, is glossed over, dismissed, and unreasearched. The article says nothing about the wisdom of weakly, patchily blocking such powerfully-driven bulk flows with impervious materials, leaving an unconsidered permeable remainder to carry the full traffic. My unresearched feeling is that it's a recipe for partial stagnation, pockets of high moisture accumulating by the familiar one-way pump mechanism, far from the possibility of re-evaporation.

Finally, nothing to do with the research project, we get the old scare of 'slump' and 'moisture ingress'. No mention of the brittle failure, shrinkage and blowing-agent loss that degrades the type of materials that Kingspan flog.

Let's not confuse this with the subject of hygrocopicity of insulants, which is something else again, and can definitely average-out and moderate peaks of internal humidity, by diffusion - but even then 'bulk air exchange' is still completely necessary, to remove the nett internal production of water vapour.

PS the PS to the article mentions an experiment that's supposed to have discredited the 'dynamic insulation' idea - yet another 'something else again'. The experiment appears to have grossly and ignorantly confused vapour permeability with bulk-air permeability. How could anyone expect a Findhorn 'breathing wall' house to provide the kind of bulk-air permeability (in-only because of maintained internal low pressure) upon which 'dynamic insulation' relies? As they say - 'no airflow occurred through the panel' No wonder the 'dynamic insulation' effect didn't show up!

This is really poor stuff.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62569#Comment_62569 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62569#Comment_62569 Wed, 23 Sep 2009 07:56:17 +0100 Mike George Posted By: fostertomI'll see if I can - it was a Canadian study on this subject, Grd Fl over 'crawl space', that you posted, that first alerted me. Do you remember what that was?

Wasn't that mineral wool? Pretty sure it wasn't PUR.

Also we are talking about the UK here, not North America where seasonal conditions are rather more varied- UK recommended construction would need to be carfully considered in this context berfore being used there.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62571#Comment_62571 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62571#Comment_62571 Wed, 23 Sep 2009 07:59:41 +0100 Mike George Posted By: fostertom
This is really poor stuff.

LOL. Ditto my second post in reply to Tony]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62572#Comment_62572 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62572#Comment_62572 Wed, 23 Sep 2009 08:00:35 +0100 Mike George Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62621#Comment_62621 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62621#Comment_62621 Wed, 23 Sep 2009 18:29:00 +0100 ali.gill http://www.wufi-pro.com/

Also Neil Mays short article on breathability is here
http://www.natural-building.co.uk/art_how_to_prevent_water_damaging%20_buildings_and%20_health.htm

Tom - I think this is the article (or 'building science insight')
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces
much much more here and on the links to the left
http://www.buildingscience.com/doctypes/digest]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62686#Comment_62686 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62686#Comment_62686 Thu, 24 Sep 2009 10:17:07 +0100 skywalker
All the NBT blurb says is it is a good idea to get your head around what is meant by breathability and list a bunch of unsubstantiated 'facts' (I'm sure many are correct but there are no references or links to supporting documentation). Unfortunately is also goes on about 'Healthy Buildings' a weasel phrase which is open to misinterpretation by both tree hugger and industrialist alike.

I remember the 'crawlspaces' document well. It provides a hugely positive endorsement for the use of PUR under floors (but does not approach what you do at the edges of course - too hard).

Watching from the fence with great interest (I have lovely breathable lime plastered walls and a superb PUR insulated roof & love them both dearly).

A bit sad really.

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62694#Comment_62694 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62694#Comment_62694 Thu, 24 Sep 2009 11:36:32 +0100 fostertom Posted By: skywalkerI remember the 'crawlspaces' document wellCan you remember any clues that wd allow you to search for it?]]> Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62696#Comment_62696 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62696#Comment_62696 Thu, 24 Sep 2009 12:30:42 +0100 Mike George http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces?full_view=1

Original discussion here http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2813&page=1#Item_8]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62699#Comment_62699 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62699#Comment_62699 Thu, 24 Sep 2009 13:01:56 +0100 skywalker
It is in the links provided by Ali.

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62700#Comment_62700 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62700#Comment_62700 Thu, 24 Sep 2009 13:08:55 +0100 Mike George
Soooo, no clear evidence so far of the interstitial condensation problems alleged of PUR then?

And nothing more refuting the article in detail?]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62702#Comment_62702 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62702#Comment_62702 Thu, 24 Sep 2009 13:14:41 +0100 fostertom
Posted By: skywalkerI remember the 'crawlspaces' document well. It provides a hugely positive endorsement for the use of PUR under floors
But not between the joists, as a simple substitute for the glass wool. They say put what you like between; the vital thing is foil-faced PUR right across beneath the joists. Actually, not even specifically that; it's any kind of insulation between, plus vitally any kind of insulation under, plus a VCL on the underside of all that. Whereas in Britain we'd automatically put the VCL on the topside of all that. That's because, for Washington DC, they deem the summer external high-humidity to be the crucial thing, not as in UK, the winter internal high-humidity.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62704#Comment_62704 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62704#Comment_62704 Thu, 24 Sep 2009 13:23:33 +0100 Mike George
Also, I have not seen a certified method of using PUR between suspended floors - so I don't go along with using it in such a scenasrio, especially adding a full sheet underneath the joists- Timber suspended floors require good sub floor through ventilation in my experience, and the underside of the joists should be exposed to it.

I haven't seen a construction type like this advocated by any PUR manufacturer. Do you know of any Tom?]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62705#Comment_62705 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62705#Comment_62705 Thu, 24 Sep 2009 13:29:41 +0100 skywalker
From the article:

"The average dew point of the exterior air during the summer months in Washington, DC is 65 degrees. Let’s bring this air into the crawlspace—so therefore the dew point of the air in the crawlspace is 65 degrees. Recall that the top of the floor joist is 75 degrees. The floor joist sees the dew point of the air in the crawlspace (we can ignore the vapor permeance characteristics of the fiberglass batt insulation since it is so vapor open—just pretend that we have air rather than insulation here—but not just any air—air with a huge temperature drop— “insulating air”), but because the floor joist is 75 degrees at this location, the relative humidity at this location is 70 percent yielding a wood equilibrium moisture content of 13 percent. The floor joist is “dry” at the top and “wet” at the bottom. Why wet at the bottom? The surface of the wood is cold, below the dew point of the air in the crawlspace and therefore condensation forms on the wood. At fiber saturation the moisture content of wood is 28 percent (go to Figure 3 again).'

So the vapour barrier in the solution is on the cold side.

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62706#Comment_62706 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62706#Comment_62706 Thu, 24 Sep 2009 13:35:11 +0100 skywalker
Warm roof upside down?

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62709#Comment_62709 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62709#Comment_62709 Thu, 24 Sep 2009 13:49:15 +0100 skywalker
Sorry Made me laugh

I'll get my coat

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62710#Comment_62710 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62710#Comment_62710 Thu, 24 Sep 2009 13:49:34 +0100 Mike George Posted By: skywalkerThe Article may set the scenario in summer but the issue is the same as here higer temp & humidity air from the inside meeting colder saturated air from the outside.

From the article:

"The average dew point of the exterior air during the summer months in Washington, DC is 65 degrees. Let’s bring this air into the crawlspace—so therefore the dew point of the air in the crawlspace is 65 degrees. Recall that the top of the floor joist is 75 degrees. The floor joist sees the dew point of the air in the crawlspace (we can ignore the vapor permeance characteristics of the fiberglass batt insulation since it is so vapor open—just pretend that we have air rather than insulation here—but not just any air—air with a huge temperature drop— “insulating air”), but because the floor joist is 75 degrees at this location, the relative humidity at this location is 70 percent yielding a wood equilibrium moisture content of 13 percent. The floor joist is “dry” at the top and “wet” at the bottom. Why wet at the bottom? The surface of the wood is cold, below the dew point of the air in the crawlspace and therefore condensation forms on the wood. At fiber saturation the moisture content of wood is 28 percent (go to Figure 3 again).'

So the vapour barrier in the solution is on the cold side.

S.


Also from the article

The ground in crawlspaces is cold,1 much colder than the outside air during the summer months. In an irony not appreciated except by building science geeks ventilation air in the summer months in most parts of North America brings moisture into crawlspaces and deposits this moisture on surfaces that are below the ventilation air dew point. In the good old days this was the ground—or the ground cover which of course is at the same temperature as the ground. It was not typically the floor framing. And who cared if the ground or the ground cover was wet as long as the wood framing was not.

Sky, I don't think we get conditions like this in the UK in Summer. I have never seen damage caused to sub floor timbers by condensation in a well ventilated sub-floor. Only damage caused in poorly ventilated floors.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62712#Comment_62712 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62712#Comment_62712 Thu, 24 Sep 2009 13:51:06 +0100 Mike George Posted By: skywalkerI haven't seen a construction type like this advocated by any PUR manufacturer. Do you know of any Tom?

Warm roof upside down?

S.

No, in a warm roof ALL of the insulation is outside of the structure.

Where insulation is between the rafters, the cold side usually requires a clear ventiated gap of at least 50mm, although some say this is unnecessary where a breather membrane and counter battens is used exernally - I always go for the air gap personally, as well as a VCL on the warm side of the insulation.

A warm 'floor' would be impractical in retrofitting floors in my opinion.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62714#Comment_62714 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62714#Comment_62714 Thu, 24 Sep 2009 14:06:41 +0100 skywalker
Apologies to Tom & Mike - as ever happy to be corrected (only way to learn).

However looking at the Kingspan site, http://www.insulateonline.com/ Insulate between and over 'sarking' insulation is one of their proscriptions for an unvented roof & I am sure Cellotex/Xtratherm etc would be the same. All they show is a membrane over the top to prevent ingress (or sell more membrane) & suggest the need for a warm side VCL or use of vapour check plasterboard be assessed!(be calm Tom don't shoot the messenger).

S.]]>
Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62715#Comment_62715 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62715#Comment_62715 Thu, 24 Sep 2009 14:10:22 +0100 Mike George Article challenging the benefit of breathability http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62717#Comment_62717 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62717#Comment_62717 Thu, 24 Sep 2009 14:11:17 +0100 skywalker
:bigsmile:]]>