Not sure one should judge the quality of a judgement on any topic on the basis of whether or not the other side joins in debate on a particular website. Life is short and they may just feel they have already said what was necessary and in an accessible way.

There is a large and quite demanding literature on the topic of breathability (and it certainly does include capillarity as an element). If you really want to challenge "the idea of breathability" to quote Phil Heath isn't the onus on you to review that literature? But it is a Masters Topic with supervising skills in systematic review at the very least and with German essential. If you want to rely on just what even Phil Heath says about breathability just think existing joist ends, sitting in a solid wall - colder now you have added insulation internally. If the insulant is closely applied to the joist and is hygroscopic, has good capillarity and a surface that encourages evaporation (yes of course ventilation will help!! along with warmth and lower water vapour pressure in room air) may be the moisture in that joist end can be dispersed. If the insulant is closely applied probably with a vapour excluding memebrane and has none of those properties the joist end cannot dry out - arrrrgh!!!!

Me thinks there is an issue here and statements like "breathability should not be a key factor in choosing insulation" are not good enough.

Title "Making the right choices for insulation" and refers to two articles from Cambridge Architectural Research (copies available on request) about a study funded by Kingspan, that show that "no bulk air flow occurred" through an existing breathing wall. In essence he is saying that "bulk air exchange" through ventilation is "more important that diffusion" for keeping humidity within bounds. A truism that I imagine all would agree with. However he then goes on to assert that breathability is "largely irrelevant" whereas longevity should be the key factor when choosing insulation.

I still want to know what would happen to joist ends and masonary sitting behind "breathing" versus impervious insulation - may be a review of published data can answer that question or may be measurement in situ is the only way. Who has measurments/can do measurements - moisture and mold please.

Posted By: bot de pailleDid strawbale construction form part of the research that informed the study?

Also I believe that there is recent research which seems to indicate that hemp lime/walls perform better than would be expected as a result of various combined factors, including such characteristics as hyrdroscopic and vapour permiability.

I thought that came down to the fact that you can build a gap free and non-slumping wall from hempcrete walls? In other words, the material is better than standard practice at reducing bulk air movement. We started looking at hemp when we were planning our house. Five years later I'm still waiting to see much more than experimental homes. It would be wonderful if this material could move forwards, but the signs so far aren't good despite very promising test results.

Posted By: bot de paille
Comparing Kingspan petroleum based products aagainst natural insulation materials is like comparing apples and oranges to say the least. They are two totaly different approaches which will behave differently and require their own best practices.

Indeed.

I would have thought that modern approaches to bulk air movement would quite possibly dwarf any effect of breathability. Passive or mechanical ventilation of various types are far more efficient at ensuring that stale air pockets are reduced to a minimum and zones of high humidity are kept under control. Compared to a traditional house with uncontrolled ventilation, the effect of the wall's breathability must be much reduced?

"I thought that came down to the fact that you can build a gap free and non-slumping wall from hempcrete walls? In other words, the material is better than standard practice at reducing bulk air movement. We started looking at hemp when we were planning our house. Five years later I'm still waiting to see much more than experimental homes. It would be wonderful if this material could move forwards, but the signs so far aren't good despite very promising test results."

Like I say the research seems to suggest that lime/hemp mixtures work on several levels due to the way the materials absorbe and release moisture, regulate humidity levels within the wall and the thermal mass properties which all add up to a thermal performance higher than would be suggested from only studying U-values. I wil have to dig out the link.
I would be interested to know what signs arnt so good despite very promisong test results for lime hemp, though this doesnt have much to do with breathability :)

Posted By: TunaI was under the impression that moisture problems inside the wall are significantly less of an issue where the humidity levels in the building are well managed?

To some extent yes, regardless of whether you do that with mechanical ventilation or by opening windows. But the wall still needs to be well-designed and built, whether it's "breathable" or not. The main effect of regulating the indoor humidity is to prevent surface condensation and mould/rot growth by stopping the humidity getting too high.

In a 'correctly ventilated' (whatever that is) domestic building , aren't the moisture levels relatively close to those outside - at least in the UK? I appreciate there's a temperature difference, but doesn't that just mean that domestic interiors have a lower relative humidity?

No, because what matters for vapour transport is the physical vapour pressure, not the relative humidity. Relative humidity is important for humans (and also for organic building materials, and microorganisms etc). Inside a building the RH is best kept between say 30% and 60% for comfort and since the temperature is also kept relatively constant at say 20 C for example that means the physical vapour pressure is between 700 Pa and 1400 Pa all year round. In winter in the UK outside RH is typically high, between say 70% and 100% but the temperature is lower, say 0 C so the vapour pressure is between 400 Pa and 600 Pa. Vapour is continually produced indoors by breathing, cooking, washing etc.

On a slightly different aspect, has anybody actually seen the CAR research reports that the article is supposed to be based on? I requested copies from Kingspan a week ago but I haven't had so much as an acknowledgment.

Cheers, Dave

I'm starting to round in tighter circles on this this one.

The Phil heath document reads well with a clear unashamed bias (as you would expect) that I have no problem with. I get a very strong feeling that something is missing however & I can't quite put my finger on it. The pictures on page 26 showing the 'consequences' of different insulation methods seems too supportive of his case. If it were properly true why can't I hear buildings falling down all around me?

I'm sure that he is confusing/combining pathways of interstitial (probably the wrong word for moisture moving about within the fabric) moisture transport with problem locations where if there were infiltration gaps where if there were warm wet air meeting a cold surface. The amounts of water involved (and their consequences for the structure) are very different. The text is also a little confusing on the 'breathability' thing and if you skim read it (introduction read properly, pick out a few bits of text from the main body, look a pictures & read conclusion) you are left with the direct impression that breathable construction is a significant factor in internal air quality and that only by using low impact materials can you achieve this. Whilst I strongly agree that using low impact materials can only be regarded as a good thing I am left with a feeling of being hoodwinked with regard to the control gaseous water in the internal environment AND water in the structure.

The other documentation -baubilogy or whatever, presents a few other points which are buzzing away in head somewhere. Firstly a nice clear 'ventilation through walls is a load of tosh'

quote(http://www.baubiologie.de/downloads/english/breathing_wall.pdf):

"As discussed above, it is a
misconception to assume that walls could “breathe” air. Despite their varying
degrees of porosity, the air pressure difference between outdoor and indoor air
is never high enough to promote a significant air exchange through exterior
walls; for a properly installed building envelope only 0 up to a maximum of 4%
of the required air exchange can be achieved this way. If air does get through a
wall, it is not through the wall itself but through poorly sealed joints, cracks and
other building component connections. This, however, is the least desirable way
to supply fresh air because it promotes high heat loss in winter, makes for very
unpleasant drafts, and potentially invites moisture problems."

I believe from the many discussions here and this thread the the last part of the last sentence is the only significant source of 'problem' building fabric moisture (at the moment!).

Another issue I find very confusing is the presence, or absence of a vapour impermeable layer. My question here is does it matter if one 'side' has an impermeable covering (dulux on your internal walls or sandtex externally). My gut feeling, i.e. that informed by years of received wisdom, is that attempting to seal an external surface which is hygroscopic (stone, wood, brick, render etc) has been established as a generally bad move) the seal is never complete or permanent and rain gets trapped behind with the commonly seen problems. But if your external surface is properly sealed (granite, glass,cement render over solid closed cell insulation, SIPS etc) there are only issues where construction fails. Internal surfaces have been sealed for many, many years however and I am not aware of 'common' problems here. It seems to me that if one surface is sealed and the rest of the structure is 'breathable' there should be no problem and the the same is true if the whole structure is impermeable or indeed permeable.

from baubiology again:

"The actual amount of water vapor an exterior wall can shuttle to the outside of a
building is rather low though it is important for drying out walls and thus for the
avoidance of moisture and mold damage. During winter when outside
temperatures are low in northern and moderate climates, only about 1 to 2% of
the indoor moisture can make it through, for example, a brick wall.v Again, it is
obvious that the majority of the moisture that is usually generated inside a home
needs to be removed through active ventilation of windows and/or mechanical
ventilation systems."

Moisture buffering is also interesting (works well in my bathroom) but it seems to it is a property which can be exploited both in a 'breathing' & non breathing construction:

from baubiology (haw meny ways can I spell this in one post!)

"Please note that this important short-term (several hours) moisture buffering
effect only relies on the first 1 to 2 cm of the interior wall surface. Thus almost
any wall structure can benefit from the moisture buffering effect by, for example,
adding a clay plaster or wood wainscoting."

The baubiology article finishes with this (actually a bit on smell follows):

'It is unclear why the “breathing wall concept” continues to persist when it is
riddled with so many misconceptions. What is clear, however, is that any building
envelope has to meet two major challenges: First, not to let any water in.
Second, if water does get in, to let it out again. In contrast to the widespread
use of vapor barriers, building biology favors the so-called flow-through design
that is transparent to water vapor diffusion but windproof and protected against
condensation water. It allows water vapor to freely pass through the wall
assembly’s components without condensing and supports drying through
capillary activity.'

A useful (ish) comment but coloured by the organisations aims & objectives (as is Phil Heath's).

Haveing taken part here, read the stuff linked to here and that I have access to at home I am left asking:

A. What is wrong with sealing the building fabric internally as long as the remainder of the fabric is able to wick away moisture should any get in through the inevitable gaps which is the situation in nearly all UK properties (thinking Dulux)?.

B. What is wrong with wrong with sealed construction if none of the materials in the core of the fabric allow the passage of moisture (SIPS).

C. What is wrong with vapour open construction (cob, stone, wood & warmcell etc etc) where the whole fabric allows the passage of moisture.

and finally...

D. Surely A & C above are actually compatible to some extent.

Now going to work on my hand made oak door latches (inspired by those Lutchens put in at Lindifarne Castle) & do some lime plastering.

S.

Thanks Peter

I think your criticism of B may be applied to all three if we assume it is a construction/post construction fault which allows air movement to create a moist spot at a suitably cool point within the fabric. In the case of SIP's this would be towards the outside of the panel or at a similar point at a bad junction?

S.

But isn't a SIP type construction just 'A' done a different way? (the insulation is structural rather than fixed to the structure). The inner face of the SIP is wood (vapour open), foam (more or less vapour closed) outer wood Vapour open, then cavity then facing (vapour open). The only part unable to 'breath' is the foam (as in A) anthing else that needs to can.

I'm not bangin' any drum just trying to get through the assumptions.

S

Posted By: djhOn a slightly different aspect, has anybody actually seen the CAR research reports that the article is supposed to be based on? I requested copies from Kingspan a week ago but I haven't had so much as an acknowledgment.

It's been a few days since I posted this, with no response. Does that mean that nobody has seen the CAR reports?

In the meantime, I've written again to Kingspan and asked them to confirm at least that I'm writing to the correct place but I've still had no response whatsoever. It seems pretty poor to write an article which bases its conclusions on reports that you promise to make available but then don't.

Can somebody else please request copies, just in case I've done something silly in my request?

Keith, have you got copies?

Just requested copies now. Interesting than no-one has a copy yet.

It does not seem to be available online for uni research purposes as yet either.

Nice find Sky.

That does mirror the content of the article. I agree with most of what is written other than points 2 and 3 on page 9, where I think both 'manufacturers equally misrepresent the situation.

For the conspiracy theorists here's a direct quote of the Cambridge Study Conclusion. I see nothing wrong with Phil Heath's interpritation of the study contents:

Conclusion
Sound construction practice is essential, in both conventional and “breathable” constructions.
Interstitial condensation is avoidable by correct placement of materials: this emphasizes the
importance of adequate data on the thermal and permeability characteristics of the materials
used. If alternatives to conventional practice are used, the construction should be modelled to
ensure dewpoint conditions are not attained within the building element. Air movement through
“breathable” panels will not attain levels sufficient to transport away moisture that has
condensed within them due to poor design, or to remedy water ingress due to building failure.
The key to creating and maintaining comfortable and healthy indoor conditions lies in good
thermal design, linked with adequate provision for ventilation through controllable routes.

There is also a list of references backing up the Cambridge study further


Boardman, B, (2008)HOME TRUTHS: A low carbon Strategy to Reduce UK Housing Emissions
by 80% by 2050, University of Oxford’s Environmental Change Institute
British Standards Institute (2002), BS5250: Code of practice for control of condensation in
buildings, BSI
Cawthorne, D. and H. Mulligan (1997). Strategic implications of large, dynamically insulated
buildings in cities. Proc. International Conference on Passive and Low Energy Architecture.
Kushiro, Japan, January 1997.
Chartered Institute of Building Services Engineers (1986), Guide, Volume C Reference Data
Crowther, D.R.G, and N.V. Baker (1993). Breathing walls: facts and fiction. Proc. 3rd. European
Conference on Architecture, Florence, Italy, 17-21 May 1993.
Department for Communities and Local Government (2006). Code for Sustainable Homes: A
step-change in sustainable home building practice, OPSI
Imbabi, M.S. and A. Peacock (2003). Smart breathing walls for integrated ventilation, heat
exchange, energy efficiency and air filtration. Invited paper, joint ASHRAE/CIBSE conference,
Edinburgh.
Oreszczyn, T., I. Ridley, S.H. Hong, P. Wilkinson (2006).. Mould and winter indoor relative
humidity in low income household in England. Indoor and Built Environment, 1 Apr. 2006, pp.
125-135.
ODPM, (2006) Approved Document L1. Conservation of Fuel and power in new dwellings, OPSI

I can report that following Keith's intervention, Kingspan have found my request and my reminder, which had both been ignored "Through oversight". They also asked me not to further circulate the document they sent me, which I regard as very cheeky given that it's one of their marketing documents. They haven't yet replied to another query I made earlier about a completely separate subject, so perhaps oversight is just a part of their corporate philosophy.

Having now read the Green Building magazine article, the background paper and the 'white paper' that skywalker pointed out, I have to say that I found them all more significant in what they didn't say than in what they did. For example, as Mike says, the conclusion of the CAR report says "Interstitial condensation is avoidable by correct placement of materials" but the report didn't discuss that and indeed the various calculations specifically excluded air movement past the edges of slabs between timber frame members and it didn't consider, so far as I can see, the permeability of the timber frame. The papers discussed breathability in relation to internal surface condensation, whereas I think the baubiologie fraternity emphasise hygroscopic behaviour rather than 'breathability' (i.e. permeability) in relation to internal condensation. Breathability, they consider, is related to interstitial condensation.

I found the most telling statement in the white paper "A mineral fibre manufacturer has made specific claims and allegations". With that in mind, the whole content is clear. There's nothing wrong or controversial but there's not much to be learned either. A storm in a teacup.

So if no one is arguing with:

Posted By: Mike George

Air movement through
“breathable” panels will not attain levels sufficient to transport away moisture that has
condensed within them due to poor design, or to remedy water ingress due to building failure.
SI

What exactly is the point of breathability then?

My A & C above:

Posted By: skywalker

A. What is wrong with sealing the building fabric internally as long as the remainder of the fabric is able to wick away moisture should any get in through the inevitable gaps which is the situation in nearly all UK properties (thinking Dulux)?.

B. What is wrong with wrong with sealed construction if none of the materials in the core of the fabric allow the passage of moisture (SIPS).

C. What is wrong with vapour open construction (cob, stone, wood & warmcell etc etc) where the whole fabric allows the passage of moisture.

and finally...

D. Surely A & C above are actually compatible to some extent.

Are clearly worded wrongly. There is no such thing as breathable construction; just construction using vapour open or closed materials. Both forms of construction work as long as the building is properly constructed and maintained and dew point position is outside of the fabric of the building.



S.

Blimey

Breathable construction is a load of old tosh!

Wool insulation isn't (made of wool), it is just more or less wooly!

What else are going to kill off today!

S.