Green Building Forum - Breathing Walls is Proven Not Workable in the Real World

Breathing Walls is Proven Not Workable in the Real World

Pingy — Fri, 03 Aug 2007 16:44:54 +0100

I picked up this comment on a different thread (http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&page=2#Item_6) and would like to know where the evidence is that proves breathing walls do not work. If it's true then should I be better off using the highly efficient petro-chemical derived insulants and not worry about having 'natural' breathable insulants?

Breathing Walls is Proven Not Workable in the Real World

tony — Fri, 03 Aug 2007 22:03:44 +0100

One problem is that many so called breathing walls have a vapour barrier somewhere inside the insulation so only the wall can breathe in and out from outside and not the house. Traditional masonry constructions do breathe moisture in and out -- more out than in. Timber frames usually have a vapour barrier so cannot do this indeed it would cause them to prematurely decay if they tried to transport moisture outwards. Many homes have so many drafts that they literally do breathe in great gulps of cold air all winter long and blow out great mouth-fulls of warm -- expensive. True breathing walls can work -- most lime and natural constructions can buffer out peaks of high internal moisture concentrations and release them slowly as the levels of humidity reduce.

What do you mean by a breathing wall?

Breathing Walls is Proven Not Workable in the Real World

Pingy — Fri, 03 Aug 2007 22:50:48 +0100

I mean breathing wall as marketed by Excel Industries (Warmcell). They call it their Enhanced Vapour Transfer (EVT) Technology. Sounds appealing when you read their literature. Has anyone got any first hand experience with this structure system?

Breathing Walls is Proven Not Workable in the Real World

Pingy — Fri, 03 Aug 2007 22:57:13 +0100

Tony, is the reason why breathing walls don't work in the real world because of what you've said, ie. they have a vapour barrier installed, thereby stopping the walls breathing?

Breathing Walls is Proven Not Workable in the Real World

tony — Fri, 03 Aug 2007 23:09:31 +0100

They just sound good. I used to think it sounded nice too but now think all it is is a sales pitch.

Breathing Walls is Proven Not Workable in the Real World

Terry — Sat, 04 Aug 2007 00:39:17 +0100

My understanding of a breathing structure is where you have an internal membrane which has a high resistance to vapour to stop vapour getting into the structure. Any vapour that does get in is then encouraged to pass through to the outside by having an outer layer which has a low resistance to vapour. A breathing structure is not one where there is a regular transfer of air through the building fabric
The inner membrane also doubles as an airtight (not vapour tight) layer, which implies ventilating to deal with moisture build-up etc. Lime as well as fermacell/sasmox board manufacturers lay claim to helping to deal with moisture changes as Tony describes.

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sat, 04 Aug 2007 08:05:44 +0100

If there is a membrane of low vapour permeability within the structure then it ain't a breathing wall - unless you know something about wearing a plastic bag over your head that I don't know.

Breathing Walls is Proven Not Workable in the Real World

fostertom — Sat, 04 Aug 2007 11:45:59 +0100

Biff's right, Terry - your with-membrane description is just the industry-standard of the last 20yrs. With an inboard vapour membrane, whether it's a full vapour barrier (very challenging to achieve) or just a gappy so-called vapour check, its resistance is so relatively high that you automatically can hardly fail to have outer layers of lower vapour resistance.

'Breathing' as described by Warmcell etc is different in principle - the powerful inner vapour resistance is avoided - the rule-of thumb is the inner-layer resistance is about 5-10 times that of the outer layer, ideally a steady gradient of resistance-values outward. Some say the ratio can be as low as 3:1. Ply/OSB inner sheathing and MR plasterboard or breather felt outer sheathing will generally achieve this - but calc those values every time! Don't go and spoil it with e.g. cement render - that will probably have higher resistance than the inboard layers.

An inner membrane isn't going to function as an airtight membrane without all sorts of non-standard detailing and unless consistently careful site work can be guaranteed.

Breathing Walls is Proven Not Workable in the Real World

Pingy — Sat, 04 Aug 2007 23:13:59 +0100

Going back to my original question is there any evidence to sustantiate the views about "Breathing Walls" being "Decaying Walls"? Or is it just the fact that everyone knows it's not possible to achieve an inner airtight membrane?

Breathing Walls is Proven Not Workable in the Real World

tony — Sat, 04 Aug 2007 23:31:45 +0100

Go on then tell us what you mean by a breathing wall please.

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sun, 05 Aug 2007 08:11:19 +0100

A wall that only uses materials of relatively high vapour permeability. Lime mortared masonry, lime render, lime or clay plaster, strawbale, strawboard, clayboard, wattle and daub, mud and stud, clay lump, earth, clay paints, limewash, whitewash etc.

No plastic.

Breathing Walls is Proven Not Workable in the Real World

tony — Sun, 05 Aug 2007 09:25:07 +0100

Thx Biff but i was asking Pingy!

Since you answered Biff, what about Victorian terraced? 1960's masonry cavity walls? modern masonry? I think they all breathe do you?

Breathing Walls is Proven Not Workable in the Real World

fostertom — Sun, 05 Aug 2007 10:08:56 +0100

Biff, can we add plasterboard, breather membranes, OSB/ply etc - anything of medium-to-high vapour permeability? Let's not put the idea about that breathing walls means only the traditional materials you listed. E.g., once multifoil insulations get proper accreditation, hopefully later this year, new versions are waiting that will combine vapour permeability with airtightness in a quantifiable way (as well as accessory products that will make airtightness easy).

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sun, 05 Aug 2007 11:12:06 +0100

I don't think vapour permeability should be muddled up with airtightness. They are very different issues. One is about stopping the draughts (in some folks eyes to such an extent that humans can't breathe). The other is about diffusion of water vapour through apparently solid, air-tight, structures. It's this latter aspect that is the matter of a building's 'breathability'. Unfortunately the science its pretty tricky, and not made simpler by incomprehensible units that are not standard between different countries. Even a thin thing like a layer of paint can be controversial. So called 'breathable' paints may be better than a standard alkyd resin but aren't nearly as vapour permeable as limewash or linseed oil paint.

Yes, doubtless there are lots of vapour permeable modern materials, but I don't know a lot about them. Old houses, typically, are mortared and plastered with lime, and the way the structure handles moisture is very different from the way a 1960s or modern wall, made with Ordinary Portland Cement, does.

Breathing Walls is Proven Not Workable in the Real World

fostertom — Sun, 05 Aug 2007 11:54:28 +0100

Yes Biff, badly put, I didn't mean to muddle airtightness with vapour permeability (or rather, its inverse, resistivity). I meant -

Most present multifoils, being peppered with quilting stitch holes, are both air- and vapour-transparent i.e. high permeability/low resistance to both (the vapour resistance they quote is for the bits between the holes - daft!).

The other types of multifoil, which have no holes because either spotwelded, or only held along the edges, are both airtight and vapour-tight i.e. low permeability/high resistance to both, like a sheet of polythene.

I'm saying multifoils are on the way that, like breather felt, combine the apparent opposites, in a quantified way:
vapour-breathability i.e. high permeability/low resistance to water vapour
with airtightness i.e. low permeability/high resistance to air.

Note that 'vapour resistance' refers only to water vapour, and 'air' is actually just a mixture of vapours, which permeate at different rates through any material. So a 'breather' membrane is only an 'airtight' membrane whose micro-holes have been fine-tuned to preferentially let H2O vapour-phase molecules through (and therefore probably CO2 and host of other vapours) but block nitrogen and oxygen molecules, as well as H2O liquid-phase molecules.

Breathing Walls is Proven Not Workable in the Real World

tony — Sun, 05 Aug 2007 14:19:43 +0100

Suddenly started to get interesting -- so a breather membrane only lets water vapour through? -- a lime plastered wall will let moisture in and out but not air or oxygen?

Sounds very much to me like Biff should have long since suffocated! Yet we hear him talking nice stuff all the time -- can someone pleaseexplain this phenomenon.

Breathing Walls is Proven Not Workable in the Real World

fostertom — Sun, 05 Aug 2007 14:38:16 +0100

Oxygen comes in the window, not thro the walls - surprised?

Breathing Walls is Proven Not Workable in the Real World

tony — Sun, 05 Aug 2007 15:57:26 +0100

Then why is Biff scared of suffocating in an airtight house?

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sun, 05 Aug 2007 16:33:43 +0100

Gosh. We still seem to be talking about air-tightness and breathability on the same thread.

As I may have mentioned before, I sleep with the window open 11 months of the year and the bathroom window is open even longer. I have wood stoves which would not work if air did not leak into the house as fast as it goes up the chimneys. The windows are double glazed but what fraught excluders there are are there to exclude draughts, not make them air tight. So I don't see much point in going overboard on the air tightness front.

I can't think why one should use multifoils, with or without perforations, but that is definately another thread.

I don't know much about 'breather membranes' and am surprised to learn that they have been finely tuned to allow water vapour through in prefernce to oxygen and nitrogen. Damn clever these builders' merchants. A lime plastered wall would, I imagine, let pretty much anything in or out, if slowly. Much like a Goretex jacket. The rain is shed but your sweat can dry out. But I wouldn't rely on even Goretex to keep me dry when dinghy sailing.

Breathing Walls is Proven Not Workable in the Real World

fostertom — Sun, 05 Aug 2007 19:23:36 +0100

Posted By: tonyThen why is Biff scared of suffocating in an airtight house?

I would be too - but then I'd arrange controlled ventilation (as it is I can see plenty of daylight round my farmhouse's windows!)

Posted By: biffvernonA lime plastered wall would, I imagine, let pretty much anything in or out, if slowly.

Not necessarily - sure to be selective, like anything permeable. Can only help, if we get to understand better how this works, then maybe tradition and 'modern' can work even better together than they can apart. Don't play the 'don't know much about', Biff - too much good sense there!

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sun, 05 Aug 2007 22:45:23 +0100

Just remind me what MNs/g-1 means,
or perm-centimeter (g/24 hrÂ·m2Â·mm HgÂ·cm) or perm-inches (grain/hrÂ·ft2Â·in HgÂ·in).

Breathing Walls is Proven Not Workable in the Real World

Pingy — Sun, 05 Aug 2007 22:51:22 +0100

To answer Tony's question.....

Posted By: tonyGo on then tell us what you mean by a breathing wall please.

I have read a lot of articles about how important it is to continue to allow old buildings to "breathe". Many of these articles use examples of how people have "improved" these buildings by coating the walls either on the outside or inside (or both) with impervious materials resulting in damp problems. This not only is bad for the building but also the health of the occupants. Okay I admit there could be a host of other reasons why the damp problems arise but the articles always seem to suggest that when the buildings are restored (improved?) using traditional materials such as lime, clay, etc. then the damp problem go away and the buildings become more pleasant places to be.

The ability of these natural materials to regulate humidity within the building is how I imagine a breathing wall to be. From a health point of view this sounds a lot more preferable than the 'plastic bag' house which seems to be linked with the increase in allergies.

The thing is when these old buildings were built there wasn't any thought about insulation. To insulate to a high level and still maintain this breathability is why I'm asking questions on this forum. If you can convince me it really isn't necessary then that's fine, please feel free to suggest how best to insulate an old building to ensure the building fabric is preserved and the living environment is a healthy one.

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Sun, 05 Aug 2007 23:01:17 +0100

Spot on Pingy, that's why insulation like Thermafleece is such a good idea. It doesn't compromise the way the old building functions yet keeps you as cosy as a Herdwick on a lakeland fell.

Breathing Walls is Proven Not Workable in the Real World

Mark Brinkley — Mon, 06 Aug 2007 06:57:21 +0100

What we are talking about here is essentially the interplay of water, air movement and heat within the building fabric. We know they are related, but we don't yet fully understand how. This leaves the way open for dozens of "theories", which all sound plausible, but are mostly unverifiable. IMHO, we still have a long way to go before we have definitive answers to these questions.

Think about it. Breathing walls, humidity buffering, vapour barriers, breather membranes, lime v cement, natural materials v synthetics, even Actis and the multifoils. They all sit in the gap that exists between theoretical physics and our limited understanding of what actually happens on site.

Breathing Walls is Proven Not Workable in the Real World

biffvernon — Mon, 06 Aug 2007 07:19:00 +0100

The profit motive sometimes blinds folk to physics.

Breathing Walls is Proven Not Workable in the Real World

fostertom — Mon, 06 Aug 2007 08:35:25 +0100

Nice summary, Mark. Add to that, as well as U value, thermal massiveness, decrement ............

Breathing Walls is Proven Not Workable in the Real World

tony — Mon, 06 Aug 2007 18:53:57 +0100

Pingy, my strong preference would be to add insulation on the outside of the walls (external insulation) Where would wou prefer the insulation to go?

Breathing Walls is Proven Not Workable in the Real World

Pingy — Mon, 06 Aug 2007 22:18:31 +0100

Tony, it would be great to externally insulate the building but unfortunately I would not be allowed by the planning department. The building has some historical interest (not listed though) and the whole reason for being able to get planning permission was to preserve it's external appearance.

Breathing Walls is Proven Not Workable in the Real World

tony — Mon, 06 Aug 2007 22:44:24 +0100

I m not sure that I agree with the notion that that means that you may not do external insulation It should be possible to do it and mimic the external appearance. Would you be allowed to make external repairs to the walls if that were needed? What is the facing of the walls made of?

Breathing Walls is Proven Not Workable in the Real World

Pingy — Mon, 06 Aug 2007 23:09:16 +0100

The building is red brick with a welsh slate roof.