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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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    • CommentAuthordaveking66
    • CommentTimeJan 4th 2021 edited
     
    Does anyone have any experience of using Isolair or Pavatherm-Combi, the Pavatex alternatives to Pavadentro, now discontinued?

    I’m planning an IWI project for a Victorian solid brick property using a breathable ‘open moisture’ system
    and am trying to find the most suitable product. Steico Therm is another Contender and seems similar to Pavatex Products. Can anyone tell me if there are any fundamental differences, and the pros and cons of the different systems.
    • CommentAuthortony
    • CommentTimeJan 5th 2021
     
    They work ok so long an no silly floor goes or has gone and repointed with cement mortar
    • CommentAuthorjfb
    • CommentTimeJan 6th 2021
     
    Pavadentro used to have a mineral layer that was supposed to minimize interstital condensation risks though I never quite understood how it worked. Not sure if the other ones from Pavatex do the same.

    I went for steico therm (not tongue and grooved) for cost reasons - much cheaper when I looked. I went for 60mm thick not any more to reduce chances of interstital condensation (with 500mm rubble walls). It seems to have worked very well.

    Is the original lime render still in tact or covered by wallpaper/paint/gypsum? You will need to get back to a flat layer of breathable render (the airtight layer as well) to provide an suitable base for the IWI boards. Anything subfloor I would use EPS.
    What are your plans at ceiling level? Best to run the boards continuously up the wall around the joists.
    I ended up mixing my own hydraulic lime/sand render for finishing over the woodfibre rather than use recommended bagged (expensive) version and it has worked well. But that may depend on who's doing it and how they want to do it.
    Wiring - may need some rethinking as sockets will move away from the wall as they are. You can always chase cable into the woodfibre if needed.

    Sorry I don't know much more about the competing products but if you need more info on installation ask away.
    • CommentAuthorkristeva
    • CommentTimeJan 6th 2021
     
    Posted By: jfbPavadentro used to have a mineral layer that was supposed to minimize interstital condensation risks though I never quite understood how it worked. Not sure if the other ones from Pavatex do the same.

    I went for steico therm (not tongue and grooved) for cost reasons - much cheaper when I looked. I went for 60mm thick not any more to reduce chances of interstital condensation (with 500mm rubble walls). It seems to have worked very well.

    Is the original lime render still in tact or covered by wallpaper/paint/gypsum? You will need to get back to a flat layer of breathable render (the airtight layer as well) to provide an suitable base for the IWI boards. Anything subfloor I would use EPS.
    What are your plans at ceiling level? Best to run the boards continuously up the wall around the joists.
    I ended up mixing my own hydraulic lime/sand render for finishing over the woodfibre rather than use recommended bagged (expensive) version and it has worked well. But that may depend on who's doing it and how they want to do it.
    Wiring - may need some rethinking as sockets will move away from the wall as they are. You can always chase cable into the woodfibre if needed.

    Sorry I don't know much more about the competing products but if you need more info on installation ask away.


    I'll probably be utilising IWI soon and will probably opt for Steico Therm, I'm interested to hear about your lime/sand render finish. Was it one coat, did you use any fibre mesh? How much cheaper than something like Lime Green Solo?
  1.  
    I used a fair bit of Pavadentro over the years. Basically the mineral layer meant you could go up to 100mm (subject to a WUFI calc) where with other products 80 might be the max. I liked it, though Pavatex products were always more than Steico and Gutex. I really like the Baumit lime plasters. So much lighter to use for an old bloke! (and an old bloke who isn't a plasterer).

    I plastered about 50m2 of Isolair recently. Seems fine.


    I know someone who used 100mm of Diffutherm as IWI before Pavadentro was available and they had no probs. Sheltered location, though, I think. Back to a condensation risk analysis as a fundamental starting-point.

    Some of the apparent differences involve the manufacturing processes - 'dry' vs 'wet', but I cannot remember enough detail to give it here.
    • CommentAuthorjfb
    • CommentTimeJan 7th 2021
     
    "I'll probably be utilising IWI soon and will probably opt for Steico Therm, I'm interested to hear about your lime/sand render finish. Was it one coat, did you use any fibre mesh? How much cheaper than something like Lime Green Solo? " - Kristeva

    I really should learn how to use the quote function - anyone enlighten me?!

    Definitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.

    For an outhouse I did it in one go. It has ended up a little weaker than the house but I think that is more down to not using an identical sand. (I used a medium and fine washed sand for the house and a fine washed sand for the outhouse).

    I remember looking at the Lime Green Solo (never used it though) as that was what was recommended. i can't remember how much cheaper it worked out but it was quite a bit. Roughly if a bag of lime 3.5 is £10 and you use 1/3 bag to 2/3 sand to equate to a bag of lime solo (£20?) you can see the difference. Downside is bagged is more uniform but so long as you are gauging your mixes all should be good.
    • CommentAuthorEd Davies
    • CommentTimeJan 7th 2021
     
    Posted By: jfbI really should learn how to use the quote function - anyone enlighten me?!
    Select the text you want to quote, press the quote button in the top right of the post you're quoting from then, when you come to press “Add your comments”, make sure that “Format comment as” is selected to Html. If it's selected to Text the blockquote tags, etc, will be displayed literally.
    •  
      CommentAuthordjh
    • CommentTimeJan 7th 2021
     
    Posted By: jfbDefinitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.

    Note that historically mesh wasn't available. People used up to 30% of horsehair in the mix instead. The current equivalent (some people still use horsehair) is polypropylene fibres in the mix. Mesh is fine, so is fibre, or a combination. Anything to increase the tensile strength of the plaster, just like concrete.
    • CommentAuthorkristeva
    • CommentTimeJan 7th 2021
     
    Posted By: jfb"I'll probably be utilising IWI soon and will probably opt for Steico Therm, I'm interested to hear about your lime/sand render finish. Was it one coat, did you use any fibre mesh? How much cheaper than something like Lime Green Solo? " - Kristeva

    I really should learn how to use the quote function - anyone enlighten me?!

    Definitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.

    For an outhouse I did it in one go. It has ended up a little weaker than the house but I think that is more down to not using an identical sand. (I used a medium and fine washed sand for the house and a fine washed sand for the outhouse).

    I remember looking at the Lime Green Solo (never used it though) as that was what was recommended. i can't remember how much cheaper it worked out but it was quite a bit. Roughly if a bag of lime 3.5 is £10 and you use 1/3 bag to 2/3 sand to equate to a bag of lime solo (£20?) you can see the difference. Downside is bagged is more uniform but so long as you are gauging your mixes all should be good.


    Thanks for this.

    It's interesting how complex this IWI is and subject to opinion, I had a builder over today, he's been in the game 30 years and is a conservation specialist working with old houses. I wanted to ask him about replacing some joists but he took a look round the rest of the house. He turned his nose up at my wood fibre idea and said that external walls only need to breathe from one side and should be closed the other. In fact he said its damaging for a wall to be vapour open on both sides! He recommended tanking my walls and then dot & dab Cellotex. I noted the fact he also said this was partly due to time factors and he wanted his clients back in their house as soon as possible.
    • CommentAuthorkristeva
    • CommentTimeJan 7th 2021
     
    Posted By: djh
    Posted By: jfbDefinitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.

    Note that historically mesh wasn't available. People used up to 30% of horsehair in the mix instead. The current equivalent (some people still use horsehair) is polypropylene fibres in the mix. Mesh is fine, so is fibre, or a combination. Anything to increase the tensile strength of the plaster, just like concrete.


    Thanks, that's really interesting. You can get horse hair quite easily and I would imagine its a little easier to use that mesh.
    •  
      CommentAuthordjh
    • CommentTimeJan 7th 2021
     
    Posted By: kristevaYou can get horse hair quite easily and I would imagine its a little easier to use that mesh.

    Our plasterer used polyprop fibres. They're just mixed in with the lime etc. I believe it's normal not to use any in the top layer, but any that do stick out of the surface can just be burned off.

    He turned his nose up at my wood fibre idea and said that external walls only need to breathe from one side and should be closed the other. In fact he said its damaging for a wall to be vapour open on both sides!

    That's a very old-fashioned view. The 'Technical Paper 15' link that somebody posted recently explains how it's a contraint that's needed if you're relying only on Glaser condensation analysis.
    • CommentAuthorjfb
    • CommentTimeJan 8th 2021
     
    Posted By: Ed Davieselect the text you want to quote, press the quote button in the top right of the post you're quoting


    testing! I think my issue was that I wasn't signed in -thanks for the pointers Ed
    • CommentAuthorjfb
    • CommentTimeJan 8th 2021
     
    Posted By: kristevaThanks, that's really interesting. You can get horse hair quite easily and I would imagine its a little easier to use that mesh.


    I forgot to say that I used fibres in all render coats apart from the finish coat (sometimes the the fibres can end up visible) as well as mesh.
  2.  
    Posted By: jfb"
    Definitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.


    This is how I did my lime plastering. I only did the first layer and mesh though and had a specialist lime plasterer come in and do the top coat - I didn't have much faith in my plastering skills to put the top layer on public display :)

    Saying that, the plasterer complemented my base coats and said I should have a go at doing the top ones too. Maybe when I do the next room on the list.

    For my ceilings I just did one coat with mesh. Once it went off a little, I went over it with a damp sponge and roughed it up, giving it a uniform 'sandpaper' type finish and taking out any trowel marks. The coarseness looks good against our exposed beams and joists and it toned down with a couple of layers of clay paint.

    It cost quite a bit to get the plasterer to put on the fine top coat of lime, so I dread to think how much it would have been to get him to do the whole job. It's funny how we learn these new skills when there is no alternative. The only time the air turned blue was when I first did a ceiling and had loads of plaster falling onto me and just could not get the mesh into the ceiling - it also kept falling onto me and covered me with lime. The problem was caused by trying to cover the ceiling with one long piece of mesh, rather than cutting it into smaller pieces and troweling them in an overlapping pattern.

    The lime plaster I bought had synthetic hairs in it, which turned out to be a good idea as I over ordered and so some of the bags have been there 5 years as I have done a room at a time and used them up. If I had horse hair in there I think the lime would have dissolved it by now!

    p.s. for the person who is thinking of not using a mesh. I wouldn't if I were you, especially on ceilings with heavy footfall. A mate of mine did that and he's forever filling in cracks in his walls and ceilings. I've not had a single crack in over 5 years in the room I did first.
    • CommentAuthorkristeva
    • CommentTimeJan 8th 2021
     
    Posted By: jfb
    Posted By: kristevaThanks, that's really interesting. You can get horse hair quite easily and I would imagine its a little easier to use that mesh.


    I forgot to say that I used fibres in all render coats apart from the finish coat (sometimes the the fibres can end up visible) as well as mesh.


    Cheers jfb.

    I don't plan to go too thick either, probably 40mm, or like you, 60mm.

    Did you make up your own render as well, or did you use Lime Green Duro?
    • CommentAuthorkristeva
    • CommentTimeJan 8th 2021
     
    Posted By: Pile-o-Stone
    Posted By: jfb"
    Definitely use a mesh (4mm grid if I remember right). For my house I did it in two goes - one layer, put mesh on and a little scratch, then finish coat. This has worked very well.


    This is how I did my lime plastering. I only did the first layer and mesh though and had a specialist lime plasterer come in and do the top coat - I didn't have much faith in my plastering skills to put the top layer on public display :)

    Saying that, the plasterer complemented my base coats and said I should have a go at doing the top ones too. Maybe when I do the next room on the list.

    For my ceilings I just did one coat with mesh. Once it went off a little, I went over it with a damp sponge and roughed it up, giving it a uniform 'sandpaper' type finish and taking out any trowel marks. The coarseness looks good against our exposed beams and joists and it toned down with a couple of layers of clay paint.

    It cost quite a bit to get the plasterer to put on the fine top coat of lime, so I dread to think how much it would have been to get him to do the whole job. It's funny how we learn these new skills when there is no alternative. The only time the air turned blue was when I first did a ceiling and had loads of plaster falling onto me and just could not get the mesh into the ceiling - it also kept falling onto me and covered me with lime. The problem was caused by trying to cover the ceiling with one long piece of mesh, rather than cutting it into smaller pieces and troweling them in an overlapping pattern.

    The lime plaster I bought had synthetic hairs in it, which turned out to be a good idea as I over ordered and so some of the bags have been there 5 years as I have done a room at a time and used them up. If I had horse hair in there I think the lime would have dissolved it by now!

    p.s. for the person who is thinking of not using a mesh. I wouldn't if I were you, especially on ceilings with heavy footfall. A mate of mine did that and he's forever filling in cracks in his walls and ceilings. I've not had a single crack in over 5 years in the room I did first.


    Thanks for the info. How much did the plasterer cost you if you don't mind me asking, was he a specialist lime plasterer?

    I must say I admire your tenacity to tackle a ceiling. It looks like I'll be over-boarding some of mine with plaster board. Most of my lime ceilings are in good shape but have cracks, does anyone know the best way to deal with this? Would a joint compound suffice.
    •  
      CommentAuthorfostertom
    • CommentTime5 days ago edited
     
    Posted By: djh
    said that external walls only need to breathe from one side and should be closed the other. In fact he said its damaging for a wall to be vapour open on both sides!

    That's a very old-fashioned view
    and completely wrong, if relying on the 'breathing' principle.

    You can rely instead on the internal vapour barrier principle, which is still the conventional wisdom thanks to the long rule of the faulty Glaser method' but if you do, that vapour barrier has to be superhumanly complete and fault-free forever, otherwise it might as well not be there. Think of a bucket of water with 'only' one small pinhole - it won't be long before all the water has passed through it to 'the other side'.

    Infinitely safer to rely on the 'breathing' principle, which puts small resistance to the passage of water vapour in all directions. For one thing, fluctuating vapour pressures equilibriate water vapour to 'breathe' both in and out, both diurnally and seasonally, not just outward as Glaser assumes.

    With 'breathing' construction it's essential to run a WUFI check for the layers of the construction relative to local climate, or to rely on previous checks for that combination. When I did that for all sorts of 'breathing' constructions, for southern England climate, I found that it confirmed that a wall or roof slope that is free to 'breathe' in as well as out performed very much better than the same but with internal vapour barrier, whether that was weak or 100% complete and perfect. In particular, the old green building 'breathing' rule of thumb for that there should be a 3 to 1 or 5 to 1 ratio, a gradient of vapour resistance from weak inside to even weaker outside, made no significant difference, for better or worse.

    Freedom to re-dry inward as well as outward is vital to the health of any wall, especially in the IWI case which puts the outer wall in danger of permanent interstitial condensation, accumulating year by year. If it can re-dry completely at least once every summer, then it doesn't accumulate. Being able to re-dry inward as well as outward doubles (?) the chance of that complete summer re-drying.
    • CommentAuthorEd Davies
    • CommentTime5 days ago
     
    Posted By: fostertomYou can rely instead on the internal vapour barrier principle, which is still the conventional wisdom thanks to the long rule of the faulty Glaser method' but if you do, that vapour barrier has to be superhumanly complete and fault-free forever, otherwise it might as well not be there. Think of a bucket of water with 'only' one small pinhole - it won't be long before all the water has passed through it to 'the other side'.
    Why does the internal vapour barrier have to be perfect if vapour can escape to the outside?

    Think of a bucket of water with 'only' one small pinhole sitting in a larger tank which has more and larger holes in it. There won't be much water lying in the tank.
    •  
      CommentAuthorfostertom
    • CommentTime5 days ago edited
     
    If the imperfect vapour barrier is inboard of a construction that happens to be like one designed to be 'breatheable', then less harm because yes the leaking
    Posted By: Ed Daviesvapour can escape to the outside
    (so why bother with the vapour barrier? which only serves to halve (?) the wall's re-drying potential).

    But if designing to be Glaser-safe, with no thought of 'breatheability', instead relying on and figuring in negligible vapour passage from the room into the wall, then an imperfect vapour barrier risks interstitial condensation. Maybe not if lucky, but for sure the construction won't be working as the Glaser calc assumes.

    What if the leaking bucket is continually replenished (internal vapour pressure is maintained) and the larger tank has no outlet (poor re-drying potential and/or dew point is reached inboard of the outside)?
    • CommentAuthorEd Davies
    • CommentTime5 days ago
     
    Posted By: fostertomso why bother with the vapour barrier?
    Because it's primarily an air-tightness layer which happens to also stop water vapour.
  3.  
    Posted By: jfb

    I went for steico therm (not tongue and grooved) for cost reasons - much cheaper when I looked. I went for 60mm thick not any more to reduce chances of interstital condensation (with 500mm rubble walls). It seems to have worked very well.


    What are your plans at ceiling level? Best to run the boards continuously up the wall around the joists.


    Hi JFb,

    Thanks for that, I’m hoping the loft insulation will mean I won’t need to do the ceiling. As it’s an eaves room, I have a short section of pitched ceiling (1000mm) between the wall and the ceiling though. The pitched section is
    lathe and plaster with nothing but a layer of roofing felt between the roof tiles. Any recommendations how I tackle this? Do I just use steico therm again with lime
    Plaster? I’m conscious the joists may not align with the sides of the room and am a bit concerned about getting a fixing on the edge of the boards.
  4.  
    Posted By: daveking66The pitched section is lathe and plaster with nothing but a layer of roofing felt between the roof tiles. Any recommendations how I tackle this? Do I just use steico therm again with lime

    It depends on the type of roofing felt. If it is the breathable type that the manufactures specs say can be full filled i.e. no gap needed between insulation and felt then you could stuff loose fill insulation in the gap.
    or
    take off the tiles etc. and do it from the top - hmm perhaps too much work.
    or
    take down the lath and plaster and insulate from underneath then reboard - messy
    or
    IWI with the Steico Therm
    •  
      CommentAuthorfostertom
    • CommentTime4 days ago edited
     
    Posted By: Ed Davies
    so why bother with the vapour barrier?
    Because it's primarily an air-tightness layer which happens to also stop water vapour.
    Exactly, so why not call it that and design it to be airtight but vapout open?

    The TV expose and scandal that nearly did for the early (1970s?) UK timber frame industry, proving terrible interstitial condensation, was answered by adoption of internal 'vapour barriers', in accordance with Glaser theory, which assumed, plausibly at the time, that the problem was diffusion of water vapour originating from internal cooking, washing etc, to places within the wall where it met dew point temperature. Mainly wrong on several counts.

    These cheap polythene barriers worked then, not because they were vapour barriers, but because they were air barriers. The passage of water vapour, originating not uni-directionally from within, but equally, diurnally and seasonally, bi-directionally from without as well, to places at dew point temperature, was overwhelmingly by carrying in bulk air movements, not so much by diffusion. To this day, air leakage is a far bigger danger than diffusion.

    So cheap polythene 'vapoiur barriers' were a vast improvement on none, for a while, until insulation levels rose over the decades, when the dangers of non-permable elements of the construction, and lack of inward re-drying potential, again began causing interstitial condensation. Glaser was discredited and more sophisticated ways of modelling, like WUFI, came in. But still Glaser is enshrined in Building Regs and in mainstream builders' conventional wisdom.

    And still even on GBF, people muddy the waters by talking about vapour barriers when they mean air barriers!
  5.  
    Posted By: fostertom
    Posted By: Ed Davies
    so why bother with the vapour barrier?
    Because it's primarily an air-tightness layer which happens to also stop water vapour.


    And still even on GBF, people muddy the waters by talking about vapour barriers when they mean air barriers!



    Hi Fostertom,

    Are they not one and the same?? As air will almost always be carrying moisture (especially air travelling from within the building), any barrier blocking air will also be blocking moisture?

    Have I got this right?
    •  
      CommentAuthordjh
    • CommentTime4 days ago edited
     
    Posted By: daveking66Are they not one and the same?? As air will almost always be carrying moisture (especially air travelling from within the building), any barrier blocking air will also be blocking moisture?

    Have I got this right?

    Afraid not. Air permeability and water vapour permeability are different characteristics. They depend both on chemical properties and on physical properties. Things that are air barriers but not water vapour barriers are quite common - they're often called 'breathable membranes'. Things that are water vapour barriers but not air barriers are much rarer and don't have the same practical importance but they do exist. (sorry, can't remember an example right now)

    edit: actually one example that does have some importance is plastic piping (is it PE or PB?) which lets oxygen through whilst containing water and therefore needs an aluminium layer incorporating to stop that. Otherwise corrosion in central heating systems.
    • CommentAuthorEd Davies
    • CommentTime3 days ago
     
    There might be some “intelligent” membranes which block water vapour and other components of the air differently (not sure) but, AFAIK, the main difference between air and vapour permeability is purely a matter of the quantities of the gases being allowed through. Letting a small amount of gas through for a given pressure would be considered vapour permeable but the quantities might be so small that it's considered airtight compared with the background leakage of even a well-built house.

    Example, VP400 [¹] “Highly vapour permeable, but completely airtight”. According to the product brochure it has a vapour resistance of 0.08 MNs/g (or 0.08 GNs/kg in SI units).

    50 pascals, the standard air test pressure, is 50 newtons per square metre so operating for an hour is 50 × 3600 = 180 kNs/m². Divide that by the resistance of the membrane to see that it'd let through 180e3/0.08e9 = 0.00225 kg/(m²·h). Air at normal sorts of temperature and pressure has a density of about 1.25 kg/m³ so that'd be an flow of about 0.00225/1.25 = 0.0018 m³/m²/h.

    Compare that with typical houses which have air permeabilities of the order of 1 to 10 m³/m²/h, so 100 times greater, and it appears, for practical purposes, completely airtight even assuming the same permeability for water vapour molecules and the other molecules in the air.

    [¹] http://www.protectmembranes.com/protect-vp400-plus-lr-vapour-permeable-underlay/p/1
    • CommentAuthorEd Davies
    • CommentTime3 days ago
     
    Posted By: djhedit: actually one example that does have some importance is plastic piping (is it PE or PB?) which lets oxygen through whilst containing water and therefore needs an aluminium layer incorporating to stop that. Otherwise corrosion in central heating systems.
    How do you know that plastic piping without an aluminium layer wouldn't let out water vapour just as much as it lets in oxygen? Are the quantities of oxygen let in enough that the amounts of water vapour going the other way would be noticeable, bearing in mind the much higher partial pressures of oxygen in the atmosphere than equilibrium vapour pressures of water, even central-heating temperature water?
    •  
      CommentAuthorfostertom
    • CommentTime3 days ago edited
     
    Very good to to see clarity in principle illustrated by figures and calcs.

    But actually AFAIK, for a given material, its air permeability will be the sum (or weighted mean?) of its different permeabilities for each of its constituent gases. Air is 78% nitrogen, 21% oxygen, 1% argon, only 0.04% CO2 (400 parts per millon), and even smaller %ages of other trace gases. All modified by greatly variable %age of water vapour, from negligible to 4%.

    The 'size' and other characteristics of the molecules of each of these, differ greatly, and this affects the permeability of a given material for each of them. So barrier materials can be designed physically and chemically to be at least somewhat selective in their permeability for, for example, oxygen, or water vapour, relative to the mixture of gases as a whole which makes up 'air'.

    This kind of selectivity shouldn't be confused with the different kind of selectivity of 'intelligent' vapour membranes such as Intello. The latter work by actively changing their physical properties depending on the current concentration of water vapour - more water vapour and the membrane's fibres swell up, thus throttling its permeability to 'air' and thus to water vapour as well.

    So when Intello fulfils its purpose, to increase its resistivity to water vapour when there's more of it around, it also becomes more airtight as well - maybe counter-productive. I don't think even WUFI takes that into consideration - WUFI's treatment of all-important bulk air movement is a recent add-on and incredibly unsophisticated compared to its treatment of water vapour permeation.

    Intello etc may have a role in the very different climate of central Europe but is best omitted (and its high cost) altogether (as well as 'dumb' vapor barriers) in maritime UK.
    • CommentAuthorLF
    • CommentTime3 days ago
     
    Water is a small fast molecule and permeates faster than oxygen and nitrogen. Then you need a driving force, just as heat needs temperature difference. Air is the same inside and out. Moisture often higher inside than out so it will try permeate. You just do not want it to condense as it gets colder.
    •  
      CommentAuthorfostertom
    • CommentTime3 days ago
     
    Posted By: LFMoisture often higher inside than out so it will try permeate
    Or, often, the reverse, diurnally and seasonally. At any rate, its vapour pressure is particularly likely to be different +/- from that of the other components of 'air' as a whole, just as its %age 0-4% is uniquely variable.
   
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