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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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Products: 100% Airtight passive house – insulation, windows etc. advice needed!

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    • CommentAuthorsteveleigh
    • CommentTimeJul 22nd 2007 edited
     
    Tony

    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 :bigsmile:. 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
    • CommentAuthorsteveleigh
    • CommentTimeJul 23rd 2007 edited
     
    Henry,

    Impervious render simply buts into the window and eliminates all the associated air barrier problems. It forms an easily maintainable mastic seal.

    Cheers Steve
    • CommentAuthortony
    • CommentTimeJul 23rd 2007
     
    I don't agree with breathing walls either but I disagree with you notion that MHVR solves all the problems. It does not. If there is any way for the water vapour in the internal air in the house to get into the insulation there will be a risk of condensation within the insulation system. The colder it is outside and the warmer it is in the house the greater the risk. The vapour barrier will have to be perfect like it is in Canada for there not to be a problem and it will have to remain perfect. I don't ever see vapour barriers installed over here anywhere like as well as they do it in Canada and theirs are inspected and tested ours are not.
    • CommentAuthorsteveleigh
    • CommentTimeJul 23rd 2007 edited
     
    Tony,

    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
    • CommentAuthorsteveleigh
    • CommentTimeAug 1st 2007 edited
     
    .
    • CommentAuthortony
    • CommentTimeAug 3rd 2007
     
    It seems to me that your system is essentially encapsulating a building in a "polyethylene bag" which is on the cold side of the insulation. As such I cannot see how it can be approved by anyone -- who are the LBC? Even with MHVR moisture in the air within the building is going to condense on the inside of your stuff and start wetting everything near it -- exactly like living in a caravan but not being able to see the condensation running down the walls because it will be doing it in places that cannot be seen. I do not think that you understand what I have been trying to explain to you about moisture in the air.
    • CommentAuthorsteveleigh
    • CommentTimeAug 10th 2007
     
    Tony if you fit a MVHR with humidistat in a caravan the walls would not stream with moisture.

    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.
  8.  
    Steve,

    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.
    • CommentAuthorsteveleigh
    • CommentTimeAug 10th 2007 edited
     
    .
  10.  
    Steve, I am open to the idea of this working, but I do not see how it can. Is there any certification we can see which backs up the LABC discussion?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 10th 2007 edited
     
    steveleigh, without a doubt ASMET has to be turned inside out - impervious structure/membrane (if any) on the inside, insulation outboard, breathable outer skin.

    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.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 10th 2007
     
    Yes i know steveleigh, I was just refering to what we'd discussed elsewhere - same principle.

    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.
    • CommentAuthorsteveleigh
    • CommentTimeAug 10th 2007 edited
     
    .
  14.  
    Steve, a shame that you do not want to continue the debate. It was just getting interesting
    • CommentAuthorsteveleigh
    • CommentTimeAug 13th 2007 edited
     
    .
  16.  
    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.
    • CommentAuthorsteveleigh
    • CommentTimeAug 13th 2007 edited
     
    .
  18.  
    Okay, I guess time will tell whether the advice you have been given is correct, I hope it works. One last question, you have listed some of the elements that make up the structure, ie ASMET with EPS mechanically fixed [to the ASMET?] What are the other elements of construction to enable an internal finish, Is there any timber at all? or are we talking laminated plasterboard backed up with mechanical fixings?
    • CommentAuthorsteveleigh
    • CommentTimeOct 1st 2007 edited
     
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