Green Building Forum - Article challenging the benefit of breathability

Green Building Forum - Article challenging the benefit of breathability Wed, 03 Jun 2026 06:08:57 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62829#Comment_62829 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62829#Comment_62829 Fri, 25 Sep 2009 19:44:00 +0100 chuckey Even if the first coats of paint are "vapour permeable", this won't be noted in the houses handbook( Cos' there won't be one) so will be over painted with a paint of the right colour rather then VP.
It is better to build with a vapour proof membrane as this would have been designed in from day one rather then just sort of appear over time.
Frank]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62830#Comment_62830 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62830#Comment_62830 Fri, 25 Sep 2009 20:45:47 +0100 fostertom Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62834#Comment_62834 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62834#Comment_62834 Fri, 25 Sep 2009 21:58:07 +0100 Tuna
It seems to me that the 'breathability' debate is massively confused by having the term cover a multitude of properties of any given construction technique, and being related to a multitude of sins. Is it mean to be a measure of the 'healthiness' of a material, of the condensation risk, of the resistance to external moisture penetration, of the ability to contribute to moisture extraction from an occupied building or something else? The one term breathability seems to be applied to all of these and suggests to me the term is overloaded - leading to confusion.

Perhaps someone could confirm if I've read the NHBC document linked to earlier correctly. It talks about systemic failures, but in the few cases where the failure was attributed to moisture condensing out from internal sources, my understanding is that the problem occurred where there was a gross failure of the structure - poor sealing or detailing around joints that subsequently allowed large volumes of air to pass through the structure. In these cases the recommended use of a vapour control layer was a substitute for correct jointing of materials and detailing around penetrations, rather than a means to manage the vapour permeability of the materials of the walls themselves?

It's interesting to me as we approach the internal fit out of our home. With SIPs carefully jointed, an MHVR and external air gaps between roof and wall cladding, Kingspan suggest a VCL is not necessary. It makes sense to me, but there are many contradictions in the debate that seem to muddy the waters.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62839#Comment_62839 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62839#Comment_62839 Fri, 25 Sep 2009 23:04:36 +0100 bot de paille Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62840#Comment_62840 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62840#Comment_62840 Fri, 25 Sep 2009 23:07:57 +0100 bot de paille Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62841#Comment_62841 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62841#Comment_62841 Fri, 25 Sep 2009 23:35:12 +0100 fostertom Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62844#Comment_62844 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62844#Comment_62844 Sat, 26 Sep 2009 08:06:43 +0100 Mike George Posted By: chuckeyI think the concept of a breathable wall is totally theoretical. Going into any supermarket to buy decorating materials, you will quickly find that they are all more or less impermeable. Coloured printed wallpaper is all plastic faced now and if you go down the emulsion route, three coats of this (done initially by the builder) will snooker any "breathability" at day one, add another coat every 5 years and the wall soon becomes impermeable to vapour.
Even if the first coats of paint are "vapour permeable", this won't be noted in the houses handbook( Cos' there won't be one) so will be over painted with a paint of the right colour rather then VP.
It is better to build with a vapour proof membrane as this would have been designed in from day one rather then just sort of appear over time.
Frank

Posted By: TunaFascinating discussion.

It seems to me that the 'breathability' debate is massively confused by having the term cover a multitude of properties of any given construction technique, and being related to a multitude of sins. Is it mean to be a measure of the 'healthiness' of a material, of the condensation risk, of the resistance to external moisture penetration, of the ability to contribute to moisture extraction from an occupied building or something else? The one term breathability seems to be applied to all of these and suggests to me the term is overloaded - leading to confusion.

Perhaps someone could confirm if I've read the NHBC document linked to earlier correctly. It talks about systemic failures, but in the few cases where the failure was attributed to moisture condensing out from internal sources, my understanding is that the problem occurred where there was a gross failure of the structure - poor sealing or detailing around joints that subsequently allowed large volumes of air to pass through the structure. In these cases the recommended use of a vapour control layer was a substitute for correct jointing of materials and detailing around penetrations, rather than a means to manage the vapour permeability of the materials of the walls themselves?

.

These two posts just about sum it up for me. Whether a wall is designed to be breathable or not; whether its timber frame or masonry; whether its clear cavity or solid is irrelevant. Its hourses for courses and all will do the job well if suited to the conditions on site.... BUT...its about converting good detailing into practice- unfortunately, we don't seem to be very good at this in the UK, and I think this is at least partially due to the bullshit and hype some manufacturers use in their selling techniques. There are many examples which we routinely discuss here- things which distort and confuse the reality - its all about selling volume to them.

So getting back to the original question - Is there a claim that breathabilty makes for healthy internal air quality - and if so is it correct?]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62845#Comment_62845 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62845#Comment_62845 Sat, 26 Sep 2009 09:37:48 +0100 marktime Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62848#Comment_62848 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62848#Comment_62848 Sat, 26 Sep 2009 10:14:18 +0100 CWatters
http://www.oikos.com/library/breathingwalls/index.html

Indoor Air Quality, Healthy Buildings, and Breathing Walls
By: J.F. Straube1 and V. Acahrya2

Quote: This paper reviews the three basic design strategies for IAQ, and the role of breathing walls. The physics of breathing walls are discussed, and the ways in which such walls can improve IAQ are outlined.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62849#Comment_62849 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62849#Comment_62849 Sat, 26 Sep 2009 10:14:37 +0100 skywalker
"Healthy House" sectionP50 "Breathing vapour permeable constructions: If water vapour can pass through the building fabric relatively easily, high humidity levels will be slowly lowered."

Whilst correct it seems unlikely that this process happens over timescales relevant to the occupants & should be dwarfed by appropriate ventilation. As established here the breathability of the structure is about protection of the structure rather than about direct effects on internal air quality.

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62852#Comment_62852 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62852#Comment_62852 Sat, 26 Sep 2009 11:02:01 +0100 CWatters Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62853#Comment_62853 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62853#Comment_62853 Sat, 26 Sep 2009 11:02:56 +0100 bot de paille Posted By: fostertomSo what better name could we give to walls/roofs etc that don't rely on strong inboard VCLs but instead minimise vapour resistance, >

"Atmungsfaehig"]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62854#Comment_62854 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62854#Comment_62854 Sat, 26 Sep 2009 11:32:00 +0100 fostertom Posted By: Mike GeorgeSo getting back to the original question - Is there a claim that breathabilty makes for healthy internal air quality - and if so is it correct?Is that all that the original question was? In my opinion, Phil Heath's article, being "... an old trick - set up a ridiculous proposition then knock it down", I readily agree that 'breathability' defined in that spurious way is nonsense - except perhaps marginally e.g.

Posted By: marktimeDoes breathability reduce the possibility of mould spore presence?

and as a robust system that will endure and perform its function for the building's lifetime, unlike the VCL membrane-based systems.

That refers to breathability using standard non-hygroscopic insulants/materials. However, breathability as a necessary factor in any use of hygroscopic insulants/materials, that's a different matter. Hygroscopics certainly make for healthy internal air quality.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62855#Comment_62855 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62855#Comment_62855 Sat, 26 Sep 2009 13:12:06 +0100 skywalker
So paraphrasing Tom (i think) the breathability, or otherwise, of the wall is irrelevant to air quality. How Hygroscopic the inner surface is clearly makes a big difference however, at least in my case.

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62861#Comment_62861 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62861#Comment_62861 Sat, 26 Sep 2009 19:40:45 +0100 Mike George Posted By: marktimeCould your question be put another way, MG. Does breathability reduce the possibility of mould spore presence?

No, it could not. Reducing the possibility of mould spore is not exclusive to whether a wall is breathable or not. The wall construction is merely one part of the equation.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62862#Comment_62862 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62862#Comment_62862 Sat, 26 Sep 2009 19:46:38 +0100 Mike George Posted By: fostertom

Posted By: Mike GeorgeSo getting back to the original question - Is there a claim that breathabilty makes for healthy internal air quality - and if so is it correct?

Is that all that the original question was? In my opinion, Phil Heath's article, being "... an old trick - set up a ridiculous proposition then knock it down", I readily agree that 'breathability' defined in that spurious way is nonsense - except perhaps marginally e.g.

Not following you Tom,

Are you saying that the article is not about whether breathable construction can have, and I quote, "a significant impact on the health of both the building and its occupants"? Seems pretty clear to me.

Or that this claim is not being made "in some quarters" as Phil Heath infers?

Where's the old trick?]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62864#Comment_62864 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62864#Comment_62864 Sat, 26 Sep 2009 20:05:21 +0100 skywalker
Suggests that VCL's arose as a reaction to very poor construction techniques. Could this be the same for the assumptions made in the generation of condensation risk assessments the Euler diagrams represent mentioned by Tom (sorry if this is not quite right).

Given that we have no one arguing for a link between vapour permeable construction as a significant factor in internal air quality is it logical to to ask if it should always be regarded as 'dangerous' to use highly vapour resistant materials in construction. I am thinking of my 'Wasp' bricks which share qualities with engineering bricks and are certainly much less permeable/hygroscopic than say stock bricks or the LBC flettons (of any flavour) I remember from darn sarf (early days in a small builders yard in Blackfen!).

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62881#Comment_62881 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62881#Comment_62881 Sun, 27 Sep 2009 08:12:33 +0100 skywalker
http://www.proctorgroup.com/index.asp?tm=26

Not picking on Proctors specially.

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62906#Comment_62906 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62906#Comment_62906 Mon, 28 Sep 2009 09:50:33 +0100 GBP-Keith
With knowledge of both sides of the coin, I believe that most any builder could create healthy and warm buildings.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62907#Comment_62907 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=62907#Comment_62907 Mon, 28 Sep 2009 10:10:19 +0100 fostertom Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63112#Comment_63112 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63112#Comment_63112 Wed, 30 Sep 2009 09:33:03 +0100 skywalker
Unfortunately the link is broken (the only one that is) but Neil May has this blurb in his promotional material (or is that shameless marketing huffing & puffing ;) ) page.

'A technical document suggesting that managing moisture with in a buildings construction is key to energy efficiency, health of occupants and longevity of the building.'

Could be an interesting read if anyone has a copy.

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63113#Comment_63113 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63113#Comment_63113 Wed, 30 Sep 2009 09:44:57 +0100 Peter Clark
http://www.natural-building.co.uk/PDF/Case%20Studies/Breathability_in_buildings.pdf

Peter]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63117#Comment_63117 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63117#Comment_63117 Wed, 30 Sep 2009 10:26:34 +0100 skywalker
Had a quick scan through (again - heave skimmed it before), loads of useful data. From the diagrams it still seems to make the assumption that a significant pathway for water in the internal air is out through the fabric. Although the text is supportive of the view that this is not the case.

Need to read this properly!

S.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63128#Comment_63128 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63128#Comment_63128 Wed, 30 Sep 2009 12:23:52 +0100 Peter Clark
http://www.baubiologie.de/downloads/english/breathing_wall.pdf

I also found this interesting;

http://www.breathing.com/pdf/indoor%20air%20quality.pdf]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63193#Comment_63193 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63193#Comment_63193 Thu, 01 Oct 2009 16:31:10 +0100 bella 1. Has breathability "sprung to light recently"? Surely not
2. Does showing that "bulk are exchange" is the major mode of removing moist air from an enclosed space really challenge the "idea of breathability".
3. Aren't the issues to do with what goes on behind the insulation at critical points (external or internal) such as timber frames, joist ends and other timber structures? Ditto masonary?
4. If you really wanted to know whether there was a functional difference that mattered between insulant materials that allowed the movement of water vapour, absorbed and held moisture and provided for ready evaporation wouldn't you investigate, under varying conditions, the substrate to which the material was attached rather that the overall moisture load of the building? Does the Cambridge study tell us?]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63197#Comment_63197 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63197#Comment_63197 Thu, 01 Oct 2009 16:59:42 +0100 Peter Clark Posted By: skywalkerMight be a good idea to get the simple stuff right first

I am in danger of becoming a Neil May bore I know but he seems to me to be saying something important..
What about his take on 'hackability' and robustness of design and implementation, mentioned in this:

http://www.nbtconsult.co.uk/articles/why_build_better.pdf

Something similar was mentioned in respect of the princes Foundation eco house on this thread:

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=4010&page=1#Item_20

Make the building envelope in a simple way, so it is practical to do it well, and design it in such a way that the wall, floor roof etc. can look after itself, without depending on a membrane or a fan or anything else. Hence the emphasis on simple construction details/materials with the three breathability properties, the wall will look after itself to an extent, even if it is not built with a great amount of care, or maintained well.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63204#Comment_63204 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63204#Comment_63204 Thu, 01 Oct 2009 19:37:58 +0100 fostertom Posted By: Peter Clarkthe three breathability propertiesWhat are these?]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63216#Comment_63216 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63216#Comment_63216 Fri, 02 Oct 2009 01:52:34 +0100 ali.gill Breathability in Buildings
"It is not only about how water moves through structures (water vapour permeability), but also about the ability of materials to absorb and release water as vapour (hygroscopicity) and about the ability of materials to absorb and release water as liquid (capillarity)."
http://www.natural-building.co.uk/PDF/Case%20Studies/Breathability_in_buildings.pdf

Some guy called fostertom responded directly to it and commented on each of 'the three breathability properties', as follows..
"V gd summary Peter, except breathability doesn't require hygroscopicity (or caplllarity) in its materials.
Hygroscopicity is something else, very beneficial, which doesn't benefit the interior (or anything) if there's a significant VCL between it and the interior.
So the hygroscopicity thing requires breathability, but breathability doesn't require hygroscopicity.
Not sure how capillarity is ever beneficial - that's materials' ability to attract, soak up and transport liquid water - is that ever good? Whereas hygroscopicity is materials' ability to do the same for water vapour."

I guess you failed to convince Peter.
In Neil's paper he breaks down the role of each of the 'three breathability properties' but your response indicates that you've not read the paper or at least are not convinced by what it says.

IMHO - And you should be able to attest to this living in a cob farmhouse Tom is that breathability is not just a one way passage of water vapour through the fabric of the building but the ability of the wall to absorb and release excess moisture as conditions dictate. I've read in a cob book that clay plaster is more effective than mechanical ventilation in dispersing excess moisture in a bathroom...It is absorbed into the wall then released through meeting equilibrium as the property is heated and ventilated through both passive and active measures.

According to BRE 'Understanding Dampness' mould spores are a risk at around 18%rh so if the wall absorbs moisture to a reasonable depth as in a cob wall or thick clay plaster then the moisture dissipates throughout the material rather than being restrained by the thickness of a plasterboard, (especially if lined with foil or pur/foam insltn). If card backed p'brd then the mould very often accumulates on the back.

And it should be remembered that this isnt just a decorative nuisance. Mould spores are believed to be carcinogenic with around 1/4 of all UK properties suffering from some form of dampness related defect affecting the interior.

Lets be honest , we're all just skimming the surface on this and unless one is prepared to spend at least two weeks reading multiple papers, website articles and delving into the British Standards on hygroscopicity of building materials then we're not going to come to any conclusive outcomes.
I find this to be a frustrating aspect of the forum. How about if we push a bit more structure into it and use an open source project management software for specific panel members/volunteers to stay focused, share subject material, study the same particular field and create a single paper (maybe using a wiki site for easy editing) that would allow for the creation of a consensus document.
Mike George has been involved in this collaborative document creation malarchy more than me so i'd be interested to hear what you think Mike.]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63217#Comment_63217 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63217#Comment_63217 Fri, 02 Oct 2009 06:52:09 +0100 Mike George Posted By: ali.gill
Lets be honest , we're all just skimming the surface on this and unless one is prepared to spend at least two weeks reading multiple papers, website articles and delving into the British Standards on hygroscopicity of building materials then we're not going to come to any conclusive outcomes.

I agree. Unless of course someone has allready gone through the studying process in such a specific area [not me!]It's this kind of expertise I try to tap into here. On the flip side of this argument is that those with a decent allround knowledge of building performance can often 'smell a rat' when shall we say 'exagerated' claims are made, especially by those with a vested interest.

It seems to me that in such cases, those who are telling porkies are often found out by their reluctance to raise their heads above the parapet. Is that the case here? If Mr Heath is wrong, surely the experts in the field of breathability would have defended their side of the debate by now? Perhaps they cannot.

Posted By: ali.gillI find this to be a frustrating aspect of the forum. How about if we push a bit more structure into it and use an open source project management software for specific panel members/volunteers to stay focused, share subject material, study the same particular field and create a single paper (maybe using a wiki site for easy editing) that would allow for the creation of a consensus document.
Mike George has been involved in this collaborative document creation malarchy more than me so i'd be interested to hear what you think Mike.

I think that's a great idea for those who have the time and motivation to get involved. Very difficult for me in the rat race life I seem to lead at the moment. And of course you would need to be sure that industrial bias where kept out. How whould you do that? For example, I have worked for product manufacturers, how do you know my views would not be slanted in their favour?]]> Article challenging the benefit of breathability https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63224#Comment_63224 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4579&Focus=63224#Comment_63224 Fri, 02 Oct 2009 09:51:14 +0100 Peter Clark Posted By: ali.gillI believe that Peter is referring to the three factors in the Neil May document that he posted midway down on page 2.
Breathability in Buildings
"It is not only about how water moves through structures (water vapour permeability), but also about the ability of materials to absorb and release water as vapour (hygroscopicity) and about the ability of materials to absorb and release water as liquid (capillarity)."
http://www.natural-building.co.uk/PDF/Case%20Studies/Breathability_in_buildings.pdf" >http://www.natural-building.co.uk/PDF/Case%20Studies/Breathability_in_buildings.pdf

Yes, I was referring to :

capillarity ()absorption/ desorption of water as liquid)

hygroscopicity (absorption/ desorption of water as vapour)

vapour permeability ( the ability of a material to allow water vapour to pass through it)

Posted By: Mike Georgethose with a decent all round knowledge of building performance can often 'smell a rat' when shall we say 'exagerated' claims are made, especially by those with a vested interest.

This is the kind of comment that I very much welcome. I must say that when I read what Neil May has written, I cannot see it as shameless drumming up of trade. He appears to me to write from the heart and to have made many good points that others have not understood or addressed.

However, he clearly has a vested interest and I have very little practical building experience. So if someone with experience smells a rat, I would like to hear about that, in detail, in a rational polite discussion, that will allow us, or me at least, to see things more clearly.]]>