Fri, 08 May 2026 08:34:40 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4940#Comment_4940 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4940#Comment_4940 Sun, 22 Jul 2007 23:52:30 +0100 steveleigh
I do not think you understand how an MVHR system works with a super airtight building envelope. The whole idea of breathing walls is proven not workable in the real world. The term "Breathing Wall" is complete nonsense environmentally speaking. The very term "Breathing wall" means the building envelope will eventually expire after using massive amounts of energy in the process of breathing in and out water molecules. Maybe it should be renamed as a "Decaying wall". Breathing walls do allow moisture to 'pump' into the insulation causing untold problems, rot, damp, 70% less effective insulation to mention a few. Its only moisture that rots things. If no moisture passes in and out of a material then it does not rot. Simple. Correct me if I'm wrong but you are saying exactly the opposite. Are you encouraging all walls to have content of water within its structure? I think that is the very last thing a wall needs. Moisture = decay and Dry = durability, long life and sustainability.

There is no pressure to force vapour into the insulation, no path is formed because the exterior skin is impermeable. Unlike a breathing wall system whereby water molecules can travel in or out depending on the pressure. Sealed airtight means no water molecules travelling through the wall because there is no pressure. The impervious skin can be maintained airtight with this system because all the places which can leak air, mainly abutments to windows and doors, can be clearly seen and therefore easily maintained "100%" airtight . The whole point of the system is to be in control of water molecules with MVHR. With breathing walls there is no direct way to control indoor moisture and vapour and air barriers often leak inside walls because of the inevitable decay of petrochemical sealing mastics and tapes and building movement.

...."The stainless steel ties are thermal bridges and seem to go through the vapour barrier.".... This is true Tony. However, approx 4 x 1mm diameter thick stainless steel wire every square metre. A square metre is million square millimetres. The thermal bridging per square metre is less than 0.004% due to the circular shape of the wire. The insulation manufacturers consider this to be zero thermal bridging.

..."leaving the choice of insulation to somebody else is unbelievable".... We do this all the time with flat roofs, the contractors, owners or architects specify the insulation to building regulations they fit it and we just turn up and cover it with impervious render. It is not cost effective to ride around the country with vans full of insulation. We will have to do things differently with thermal cladding because we will (contractors) be doing the whole job.

Cheers Steve]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4941#Comment_4941 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4941#Comment_4941 Mon, 23 Jul 2007 00:03:42 +0100 steveleigh
Impervious render simply buts into the window and eliminates all the associated air barrier problems. It forms an easily maintainable mastic seal.

Cheers Steve]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4952#Comment_4952 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4952#Comment_4952 Mon, 23 Jul 2007 13:23:21 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4961#Comment_4961 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=4961#Comment_4961 Mon, 23 Jul 2007 18:47:20 +0100 steveleigh
I think you need to understand how airtight the impervious membrane is. It is easy to work with and we can perform seamless joints with the material and maintain a watertight/airtight membrane. Even if damaged we can easily repair it to airtight integrity. You could build an aircraft structure out of this material and it would remain airtight. It is very versatile and it is not like the materials we are used to in the building trade. It has exceptional performance characteristics far more than you've ever come across. Its molecular structure is so dense it will not allow water molecules to pass through it. Even in a freeze thaw test cycling over a period of 10 days and it still has original mass. Its like putting your house in a seamless stainless steel jacket with out the problems inherent with with stainless steel i.e. welding issues and fatigue fractures.

I'll try describe what I would believe would happen in a house which is cladded with an impervious membrane in simple terms. I don't mind being corrected. Mark Brinkley's web site says (www.housebuildersupdate.co.uk) there is 10000 litres of water contained in an average detached house building fabric. Ok say a house produced 3000 litres of water a week after opening doors, showers, boiling water etc. If MVHR extracted 5000 litres per week. Where would the other 2000 litres come from? I think the water would come from the building fabric because no water molecules are coming through the walls or the roof. Therefore, the occupant can tweak their MVHR for their own comfort to different levels. It is then possible to maintain a low enough moisture content in the envelope that it will not encourage rot, mould etc. It doesn't really matter what moisture content is in the insulation because the ocupant is managing the full moisture content of the building. Do we need vapour barriers? Surely if moisture gets in the insulation then we want to get it out so it doesn't gather there causing rot, mould etc. Moisture doesn't become a danger if it is managed properly. With a normal breathing wall system it is impossible to manage.

The Canada comments do not make sense to me because technology is not country specific. It is company specific and if we want it they'll sell it. Canada are just early adopters of this technology because they felt a stronger need due to their climate.

Personally I think the ultimate wall build up would be 9 inch concrete block wall as humidity buffer and thermal mass with Impervious cladding on the exterior. Then there would be no issues with detailing for vapour barriers and air barriers inside walls. It would simplify the way houses are built. It would let the builders go back to laying blocks and we will come along and upgrade the structure to passive house standard. This sounds reasonable to me. What do you think?


Cheers
Steve]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5234#Comment_5234 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5234#Comment_5234 Wed, 01 Aug 2007 07:49:47 +0100 steveleigh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5265#Comment_5265 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5265#Comment_5265 Fri, 03 Aug 2007 00:11:13 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5497#Comment_5497 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5497#Comment_5497 Fri, 10 Aug 2007 08:14:23 +0100 steveleigh
A good example of ‘a building in a "polyethylene bag" which is on the cold side of the insulation’ would be a jumbo jet. Travelling at 35,000 feet packed with people it is plain that there is a large moisture producing mechanism via peoples breath and freezing temperatures exist outside a very thin insulated envelope and yet no streaming walls and comfortable temperatures prevail. How does this compare with our leading edge house building technology?

We need sealed buildings which will remain airtight and consistently perform to aircraft standards but instead of recycled air, which is the case in aircraft, we can have filtered fresh air provided by a well designed MVHR system.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5498#Comment_5498 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5498#Comment_5498 Fri, 10 Aug 2007 08:46:21 +0100 Mike George
I think the concern is that without a totally impervious mambrane on the warm side of the insulation, moisture will migrate into the fabric and eventually condense on the outer [cold] leaf of the building.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5499#Comment_5499 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5499#Comment_5499 Fri, 10 Aug 2007 09:18:41 +0100 steveleigh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5501#Comment_5501 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5501#Comment_5501 Fri, 10 Aug 2007 09:39:20 +0100 Mike George https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5505#Comment_5505 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5505#Comment_5505 Fri, 10 Aug 2007 09:54:07 +0100 fostertom
Putting the impervious membrane outboard of the insulation, with or without an additional internal vapour barrier (which must remain 100% perfect for the life of the building or fail completely) and with or without internal dehumidification or MHVR, is begging for problems. It's hopelessly non failsafe. Aircraft only have to last short life, are maintained regardless of cost, and actually produce the nastiest health-sapping climate that we ever consent to stay in for any period of time.

That's not only because the economics of cheap air travel depend upon the stingiest possible introduction of fresh air, recirculation maximised to the limit, dehumidified and chemically treated - it's so energy-intensive compressing sparse 6-mile-high air to normal density. The air-gulping superchargers on 2000bhp (6-second standing-start quarter mile) V8 dragsters used to be adapted from ex-DC3 cabin compressors - and they were only for 2-miles high air.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5508#Comment_5508 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5508#Comment_5508 Fri, 10 Aug 2007 11:12:11 +0100 fostertom
External encapsulation - asking for trouble. This idea of rigidity/encapsulation seems to be embedded in ASMET/Roofcrete circles. Not only the structural rididity of ASMET monocoque, but now the analagous hygrothermal encapsulation. It's a high-risk approach because all is well while the system (structure, membranes) functions 100%, but it fails utterly when the slightest thing goes wrong. "Pride (read rigidity) goeth before a fall". Paradoxically, it does seem that Roofcrete as a roof membrane has structural properties quite the opposite - resilient and repairable. - but hygroscopically I'd never use Roofcrete without through-ventilation beneath, so that its dangerous effect as an encpsulation layer is taken out of the picture. John Maniex told me of the problems experienced with Roofcrete on the Downland Gridshell, exactly on this issue.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5524#Comment_5524 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5524#Comment_5524 Fri, 10 Aug 2007 18:34:57 +0100 steveleigh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5528#Comment_5528 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5528#Comment_5528 Fri, 10 Aug 2007 20:33:14 +0100 Mike George https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5591#Comment_5591 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5591#Comment_5591 Mon, 13 Aug 2007 07:51:02 +0100 steveleigh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5595#Comment_5595 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5595#Comment_5595 Mon, 13 Aug 2007 09:27:57 +0100 Mike George Posted By: steveleighTony questioned moisture (if there is some excess moisture in a well designed MVHR system) condensing on the inside of an exterior cladding. This is not a problem with EPS insulation and a cladding product which is not degraded by moisture, it will simply run down and drain out of the wall via a drain valve.

Steve, my concern is the same as tony's. Isn't there always moisture in the air, no matter how well you control it with MVHR? What happens when the occupants open and close doors, windows etc. Without a vapour barrier on the warm side of the insulation, moisture will migrate to the cold surface of the external cladding. Is EPS totally unaffected by moisture? What holds it in place? Is it glued? or held between timber studs? Is there any timber in the construction? Are all of the component parts unaffected by moisture?

I am not sure that a simple drain is good enough, you are assuming that all of the moisture will run out via gravity when you want it to, surely some will remain on the surfaces of the component materials. The effect of external temperature on the fabric will surely mean that any moisture will constantly be changing from liquid to vapour and possibly even ice.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5607#Comment_5607 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5607#Comment_5607 Mon, 13 Aug 2007 15:06:15 +0100 steveleigh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5609#Comment_5609 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=5609#Comment_5609 Mon, 13 Aug 2007 15:58:59 +0100 Mike George https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=7499#Comment_7499 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=320&Focus=7499#Comment_7499 Mon, 01 Oct 2007 14:52:29 +0100 steveleigh