Condensation on the frame of new aluminium windows

[typonaut]

In none of your examples are you actually removing the water vapour that is causing the condensation. Water vapour in your home is created by very simple things.....Breathing, cooking, baths, showers etc. If water vapour is trapped in your house it WILL condensate on any Cold point. The only way of getting water vapour out of your property is to allow ventilation, usually by opening a window, or you could fit an extractor fan that are widely available to use in Double Glazing.

You know what, I actually understand that point, because that's precisely the point I'm trying to make: you cannot actually get rid of water vapour in the air, because it is a natural part of the environment. Well, you can get rid of it, with condensers, etc, but you can't also live in the same space (because you being there and breathing will put water vapour back into the air).

But, the science is (wow, look it up, see if I am not lying) that water vapour in the air, or humidity, only condenses upon cooling (otherwise it would not be "water vapour" it would be "water", or as we are currently concerned, condensation). So, what you need to do in order to prevent condensation is to stop the air cooling or to warm the surfaces (this is effectively what you when you blow air over glass to clear it of misting). This is why radiators are generally placed under windows.

The neat trick of humidity is that the air has a higher capacity for water vapour the warmer that air is (ie when it cools it condenses - that's how condensers work). It follows from this that, if you do not have condensation all over your property, you only have localised condensation, then you need to eliminate the cool spots that are causing the condensation.

Now, you don't know the inside of my flat, and I do, so I can tell you, with some confidence, that the only cool spots are on the aluminium window frames. If these are insulated with the use of uPVC, then the next cool spot will be the glazing itself. My experience so far is that the glass very seldom shows any condensation, even when it is very cold.

An analysis of this FACT, seems to suggest that, at worst, I'll get a few more degrees of outside chill before I get condensation on the glass. At best I may eliminate it.

You can try a little experiment yourself. Take two identical glasses, put one in the fridge and one in your general living space, leave them for 24 hours. Now take the one that has been in your general living space and breath on it - the probability is that you will get no condensation. Take the one from the fridge, and it will probably start showing condensation as soon as you expose it to a warm room - if not, just breath on it and you will see condensation.

What you have just demonstrated is localised cooling, which can be eliminated.

In answer to your questions on Aluminium vs Upvc...Aluminium is a metal and inherently colder than upvc.

This I would really like to see. Please take a piece of uPVC and a piece of raw aluminium, place them in the same environment for 24 hours, then take a thermometer and measure the temperature of each. What you will find is that they are at exactly the same temperature.

The reason aluminium "feels" cooler than uPVC is that the former is a good conductor of heat (and electricity) while the latter is not. The reason uPVC windows perform better than aluminium is again due the the conductivity properties of each compound.

As for putting a trim over the existing Aluminium, i'm afraid i can not see this helping that much, as the base frame will still be cold, so the ' trim ' will also be colder…

Again you are failing on the science here, and also ignoring the FACTS I have already presented. If you put a uPVC trim over aluminium you instantly reduce the aluminium's ability to conduct heat – or at least you insulate the warm air from the cold aluminium, which prevent condensation. Conduction is the reason the aluminium feels cold. The aluminium is transferring the cold from outside to its inside surfaces (or rather it is conducting the heat away from the inside surfaces - but we won't dwell on that issue).

I already know that using such a trim does work, because I KNOW that part of the frame that the double-glazed units sit in is raw/anodised aluminium, and this part is covered by a uPVC trim. This part does not suffer condensation issues.

What you are essentially arguing is that there is no such thing as localised cooling, and that this cannot be eliminated. I trust that I have already proven that this is wrong.

You are also basically arguing that even if you had triple or quadruple glazing you would still get condensation, or that uPVC frames would not make a difference - which is also obviously false.

I accept that if you have a damp home, you will get condensation on cold spots. But that is nothing like the same thing as trying to tackle localised cooling on surfaces that are known to be good conductors.

What I am asking is whether anyone can point me towards sources for the uPVC trim, not really whether you grasp the science or not.

 

[crank39]

We can point you to 101 different pvc trim retailers, in fact just google 'building plastics', I'm sure you'll feel like a fat kid in a sweet shop once your in there, so good luck and hope it all goes well for you.

What you won't find in there is the correct type of pvc trim, ali windows were sometimes cloaked in a pvc trim on the inner side, I believe the correct term was 'composite', but that type of pvc clipped on or slid on the ali extrusion and was hollow or chambered so in effect it was touching the ali in minimal places.

It seems as though you've come here asking for advice on how to cure your 'localised' condensation with an hair brained idea that covering the ali with pvc will do the job just hoping that we all agree effectively answering your own question

If you think pvc windows purely by their design don't suffer from condensation then you are absolutely 100% wrong, I can show 11 photos right now of condensation/mould damage around 3 pvc windows that I looked at last Friday, if you need more evidence and if I can arsed I'll download another 100 jobs for you to look at that I've seen in the last 4 years

Good luck with your trims any how!

 

[typonaut]

If you think pvc windows purely by their design don't suffer from condensation then you are absolutely 100% wrong…

I never wrote or implied that. What someone else wrote was that uPVC suffers less than aluminium. I think that's obvious, and the reason for that is that uPVC does not conduct anywhere near as well as aluminium. That's really my only point here.

…I can show 11 photos right now of condensation/mould damage around 3 pvc windows that I looked at last Friday, if you need more evidence and if I can a***d I'll download another 100 jobs for you to look at that I've seen in the last 4 years

I did not realise that you were an expert in the field. But perhaps you can answer the question that's currently nagging: what is the ideal level of humidity in a home so as to avoid condensation?

 

[AronSearle]

Some people on this forum are obsessed with ventilation. Condensation can be caused by nothing other than excessively cold surfaces, low humidity in a house still won't stop condensation forming on a coke can taken out of the fridge. If condensation is forming nowhere else except for the windows, blame the windows. Just because you can fix it by increasing ventilation doesn't mean it's the correct fix. without fancy heat recovery equipment, more ventilation will mean more heat loss, and yes that does defeat the point of getting flash new windows.

Modern windows have to achieve certain thermal values, but IIRC they don't have to avoid cold bridges, just an overall u-value.

Sorry OP, seems you got crap windows. Likely not much you can do if the supplier acts disinterested as they will likely still pass whatever standard they need to pass.

The suggested fixes of plastic trims, or other, will increase surface temperatures and so reduce condensation. The difficulty is making sure you don't miss any spots and seal it properly to avoid condensation forming behind the trim.

In this case ventilation will stop condensation, but the problem is cold bridging, so ventilation is not solving the actual problem, just a symptom.

 

[AronSearle]

I can show 11 photos right now of condensation/mould damage around 3 pvc windows that I looked at last Friday

Made in Britain I assume.

Can't stand the shoddy workmanship of cheap crap windows in this country.

 

[ronniecabers]

Some people on this forum are obsessed with ventilation. Condensation can be caused by nothing other than excessively cold surfaces, low humidity in a house still won't stop condensation forming on a coke can taken out of the fridge. If condensation is forming nowhere else except for the windows, blame the windows. Just because you can fix it by increasing ventilation doesn't mean it's the correct fix. without fancy heat recovery equipment, more ventilation will mean more heat loss, and yes that does defeat the point of getting flash new windows.

Modern windows have to achieve certain thermal values, but IIRC they don't have to avoid cold bridges, just an overall u-value.

Sorry OP, seems you got crap windows. Likely not much you can do if the supplier acts disinterested as they will likely still pass whatever standard they need to pass.

The suggested fixes of plastic trims, or other, will increase surface temperatures and so reduce condensation. The difficulty is making sure you don't miss any spots and seal it properly to avoid condensation forming behind the trim.

In this case ventilation will stop condensation, but the problem is cold bridging, so ventilation is not solving the actual problem, just a symptom.

So people on the forum are obsessed with Ventilation, may I suggest you read the document from the GGF that a link was provided earlier in the thread, the first suggestion to AID condensation is ventilation. So you are implying the GGF do not know what they are talking about??
You always have to accept a certain amount of water vapour within a property, especially without expensive heat exchangers, that is a fact due to the nature of how it is formed, there is no counter arguement to this. Condensation is indeed , just excessive water vapour coming into contact with a cold surface, that we can all agree on. What is also very apparant is that MODERN uPvc is designed to keep heat in your property, it is NOT designed to eliminate condensation, never has been , this is just a by product and even then it will only help , it will never eliminate , as the inner pane of glass is retaining heat due to the coatings used on the glass and the use of heat retention gases , such as Argon and Xenon. Modern Upvc frames also have many ' air breaks ' within the internals of the frames you can not see ( unless you cut up a frame ) and thus help to keep the house warmer via ,as has been mentioned , ' thermal ' breaks. Older frames , especially Aluminium, suffer much more as when they were manufactured the technology and benefits were not fully understood as to what could be achieved. I , personally, would never sell aluminium frames for a domestic customer due to the increased chance of Condensation on the colder metal surface ( due to cold transference from outside ) , I cannot 100% ( or even 50% ) say about the make up of a modern Aluminium Frame has or has not the same ' air breaks ' within the frame or not , and in the case of the OP, as the frames are so new , I would be asking questions to the supplier as to the internal make ups, but be prepared to be questioned on whether you have washing drying within the property, whether you have extractor fans on when cooking or bathing....all these activities increase the level of water vapour.
As for Plastic trims over Aluminium frames , by all means try, but I do not think you will find any difference whatsoever, and will be wasting your time and money.
On a side note , if you do not ventilate your property , I would be willing to bet a hard earned cup of tea, that you will have black mould growing within your property somewhere, and blackmould around a window , is not necesarily a sign of a poorly made window , there are far too many variables...such as quality of fitting , cold spots within the cavity, and back to our favourite water vapour collecting on a cold patch

 

[AronSearle]

the first suggestion to AID condensation is ventilation.

Yes? doesn't mean it is always right. We can only work on facts provided by the OP, those facts indicate the problem of condensation is only happening on the window frames = crap windows. He may have purchased cheap alloy windows, he may have purchased premium, it is not right to blame lack of ventilation when it is only (according to facts provided) happening with the new window frames.

Recommended internal humidity levels for a home range from 30-55%, Lower than 30% is considered unhealthy and uncomfortable for human health. Given an average of 40% humidity, perfectly acceptable, condensation will form on surfaces with temperatures of 8C or lower (and 55%H = 11c). If the windows allow enough cold bridging and surface radiation to allow these temperatures, it is an issue of poor window design, not ventilation or excessive humidity

Such surface temperatures have been seen on single glazing, and poorly made or designed windows and window surrounds.

So you are implying the GGF do not know what they are talking about??

No just you. Their guidance is general, and provides no specifics about humidities or acceptable surface temperatures, they also say in their guidance about cold bridging on aluminium windows, so please read the guidance you want to use as a weapon of knowledge.

If condensation is only forming on the window frame, it is not reasonable to instantly assume internal humidities are high, but rather that the window has a poor design and construction that allows excessive cold bridging.

 

[typonaut]

AronSearle, thanks for posting, I was beginning to think I couldn't get anyone to understand the basic point I was trying to make.

Recommended internal humidity levels for a home range from 30-55%, Lower than 30% is considered unhealthy and uncomfortable for human health. Given an average of 40% humidity, perfectly acceptable, condensation will form on surfaces with temperatures of 8C or lower (and 55%H = 11c). If the windows allow enough cold bridging and surface radiation to allow these temperatures, it is an issue of poor window design, not ventilation or excessive humidity.

I did a little experiment today with a scientific digital thermometer that I happen to have. In the middle of the living room the temperature was 21°C, on the window sill it was 16° and just outside the window it was 14°. I couldn't measure the temperature of the aluminium frames or the parts that are covered in uPVC (because the device doesn't work on a contact basis like that). What surprised me was how close the window sill temperature was to the outside temperature - almost as if the double-glazing was doing virtually nothing to insulate the room from the weather outside.

I also did a little research on humidity and dew points, and found, as you wrote, it doesn't take much of a temperature drop in order for condensation to form. In my test, on a mild day, if we guessed that the humidity in the room might be at 50%, then the 5° drop at the window sill will increase the humidity there to around 75%. It doesn't take much imagination to realise that, if the windows are really doing that poor a job, then on a cold day condensation is going to form very easily - even if you are at the lower end of recommended humidity to start with.

Just to be clear, the windows in this flat are around 20 years old. If I was able to I would probably just replace them - but they are the responsibility of the freeholder, and I can't really do anything with them other than in non-structural ways.

There are two different posters asking similar questions in this thread - the other poster, with a similar problem, had newer windows.

 

[ronniecabers]

the first suggestion to AID condensation is ventilation.

Yes? doesn't mean it is always right. We can only work on facts provided by the OP, those facts indicate the problem of condensation is only happening on the window frames = crap windows. He may have purchased cheap alloy windows, he may have purchased premium, it is not right to blame lack of ventilation when it is only (according to facts provided) happening with the new window frames.

Recommended internal humidity levels for a home range from 30-55%, Lower than 30% is considered unhealthy and uncomfortable for human health. Given an average of 40% humidity, perfectly acceptable, condensation will form on surfaces with temperatures of 8C or lower (and 55%H = 11c). If the windows allow enough cold bridging and surface radiation to allow these temperatures, it is an issue of poor window design, not ventilation or excessive humidity

Such surface temperatures have been seen on single glazing, and poorly made or designed windows and window surrounds.

So you are implying the GGF do not know what they are talking about??

No just you. Their guidance is general, and provides no specifics about humidities or acceptable surface temperatures, they also say in their guidance about cold bridging on aluminium windows, so please read the guidance you want to use as a weapon of knowledge.

If condensation is only forming on the window frame, it is not reasonable to instantly assume internal humidities are high, but rather that the window has a poor design and construction that allows excessive cold bridging.

So I do not know what I am talking about, yet all I did ( and have done ) is say that ventilation helps with condensation , exactly what GGF said.

Firstly I am going to ask two questions and would like your input on them...
1/ I am in my kitchen , boiling some potatoes, the room is starting to fill up with water vapour ( very visible as its steam! ) , and therefore my windows and walls are beginning to Condensate, I think , ah, I'll put on the extractor fan, thus VENTILATING the room, and lo and behold the quantity of water vapour reduces, visibly and I can no longer see any steam....What happened there then?

2/ I have a Tumble Dryer that has a vent on it ( a non condensing dryer ) ...why would I have to put the vent out of a window?

Going back to the OP, who seems to have vanished it would appear, they asked if they should go back to the supplier of the windows or investigate the cause of the Condensation. Well there are a couple of things, which I did point out in my post, which AronSearle, you are ignoring, firstly , Is there anything causing excessive moisture ( eg Drying Clothes etc ) and secondly how well the windows are fitted. The second point is very hard to prove , but if , and I mean a Big If, the windows have not been fitted correctly then there is a possibility of Heat transference around the window itself, therefore making the windows colder. Without further explanation and investigation you CAN NOT say that the windows are , in your words , Aron, ' crap ' , as that is your opinion on very limited information . That would be like me saying your haircut was crap , as I have no real information on it! You do not know if the OP had condensation on the windows previously, if so the windows are not at fault.

Windows will always be the coldest point of a house , due to how thick they are, hence why typonaut, you have readings that are closer to ouside temperature. My walls are nearly 3ft thick and made of solid stone, there is no way on this planet that a window frame that is 60mm , 70mm or even the depth of a Upvc Sliding sash at 150mm , is going to keep as much heat in. If you stuck a heater on your window sill , yes , the temp of the window would rise , and the condensation would vanish from the window, but all you have done is remove the water vapour back into the air, and it will find another cold spot to ' condensate ' on .

The key to all of this is managing the water vapour in your property, the simplest and cheapest way is through ventilation , albeit , in winter not ideal. Extractor fans in bathrooms and kitchens are also very useful. I have no knowledge of how Heat Exchangers work, or how expensive they are, but bet they are not cheap.

Typonaut , just to clarify, your windows are 20 years old...new windows WILL NOT eliminate condensation ( it will aid with the visible signs on the windows , but it doesn't disappear as if by magic, the airbourne vapour is still there, until you either let it out , or dry it out ),as trimming over the existing windows also won't, you need to deal with the causes of water vapour.

If you wish to have a water vapour free house , and thus no risk of condensation ever....brick up all your doorways and windows and any other opening, turn off your water supply, seal the house up so no air can get in ( or out ) and walk away...even then I bet you get some in there...
Water Vapou is every where...inside , outside, we breath, animals breath, we sweat, we cook, we bathe.....You are never going to eliminate that risk of condensation.

Water Vapour ..........Cut down the quantity produced, let it out the property or dry it out.....simples!

 

[typonaut]

Typonaut , just to clarify, your windows are 20 years old...new windows WILL NOT eliminate condensation ( it will aid with the visible signs on the windows , but it doesn't disappear as if by magic, the airbourne vapour is still there, until you either let it out , or dry it out ),as trimming over the existing windows also won't, you need to deal with the causes of water vapour.

I think the problems here are twofold: first you don't seem to be able to understand that condensation can be dealt with other than through ventilation (which kind of negates the idea that better performing windows have fewer problems with condensation) and that although you seem to be able to grasp that humidity is a normal part of life in the home, you don't seem to be able to recognise that a temperature drop at what was "normal" humidity leads to condensation.

That is to say that 50% humidity at 20° leads to condensation at around 10°. If you have a localised cooling problem, then it can mean that condensation in that area is just an indicator that humidity in other areas of your home is in the *normal* range.

If you can eliminate the localised cooling, then you may eliminate the condensation. At worst, you will avoid condensation for a few degrees more - because you have at least slowed down the heat transfer.

 

[AronSearle]

If you wish to have a water vapour free house , and thus no risk of condensation ever

Uh uh, straw-man arguments and misunderstanding of condensation physics. Condensation happens when internal surfaces are cold vs internal humidity and temperatures. And no, I am not talking of specific examples of boiling water in kitchens, or unventilated tumble dryers. The issue at hand is overall average conditions, not temporary peaks during showers/cooking.

Well designed thermally efficient windows, will maintain inner surface temperatures high enough to avoid condensation. The problem with this country is that far to many of the windows we manufacture are cheap and rubbish, often we see good double or triple glazing, but very poor frame designs with inconsistent thermal breaks (or none). Made worse by poor fitting, often with badly fitted or missing insulated cavity socks.

When condensation is only forming on the window, or window surrounds, it does not mean internal humidities are excessive, but rather internal surface temperatures are too cold.

You can stop condensation forming on a cold can of drink by ventilation, doesn't mean you should.

I did a little experiment today with a scientific digital thermometer that I happen to have. In the middle of the living room the temperature was 21°C, on the window sill it was 16° and just outside the window it was 14°. I couldn't measure the temperature of the aluminium frames or the parts that are covered in uPVC (because the device doesn't work on a contact basis like that). What surprised me was how close the window sill temperature was to the outside temperature - almost as if the double-glazing was doing virtually nothing to insulate the room from the weather outside.

I also did a little research on humidity and dew points, and found, as you wrote, it doesn't take much of a temperature drop in order for condensation to form. In my test, on a mild day, if we guessed that the humidity in the room might be at 50%, then the 5° drop at the window sill will increase the humidity there to around 75%. It doesn't take much imagination to realise that, if the windows are really doing that poor a job, then on a cold day condensation is going to form very easily - even if you are at the lower end of recommended humidity to start with.

Yea, it is a bugbear of mine.

Lot's of poor windows out there, where condensation can occur with humidity levels in the mid 30's% when outside temperatures hit near zero.

Look at some of the Nordic windows, their standards are much higher and designing out thermal bridging to avoid condensation is more widely practised and expected (think about how cold it gets there and how much better the windows have to be to avoid condensation). In fact their windows are generally so much better, that the problem of external condensation is more widely known and understood, not many of our windows are thermally efficient enough to encounter that problem, and the few times I have dealt with people who have encountered it here, were completely baffled and surprised.

I've also encountered a situation where the window had top quality triple glazing, but cheap alloy frames. They had external condensation on the glazing on some days, and internal condensation on the frame on cold days, it was such an absurdly poorly made window.

 

[ronniecabers]

The issue is to do with peaks of humidity levels....can't you see that! If you have extra water vapour being added to the building through bathing etc...where does it go?
Condensation Physics in a nutshell, are warm moist air settling on cold surfaces , forming water droplets. So to you average conditions are when nobody is doing anything in the property, to completely ignore bathing, cooking 'peaks ' etc is very shortsighted

Also You did not answer either of my questions so I can only guess you can not answer them!

Can I ask how you know , and under what knowledge , you say the windows manufactured in this country are cheap and rubbish?
Do you know the make up of modern Upvc, Aluminium and Wood windows for a fact, to say they are rubbish?
, are you going to go to the likes of Anglian Windows and Everest and tell them their product is rubbish , are you going to tell all their customers that the product they purchased is rubbish?

The condensation is only forming on the window, or window surrounds because they are cold....yep I agree with that , because as I stated you are never going to get a window to offer the same thermal properties of a wall...but the underlying issue is the amount of Humid air...
Cut down the amount of Humid air and your condensation levels will also drop...quickest , cheapest and easiest solution is ventilation

You also go onto to say that Nordic windows are much better , that they have the problem of external condensation...Well I have a surprise for you....Modern day UPVc windows in the UK ALSO suffer from external condensation and have done since at at least 2010 when the Building regulations stated that Windows had to have Energy Ratings.
Your last comment about triple glazing.....external condensation ...window doing job...internal condensation...this is not absurd if the level of water vapour/humidity in the property is very high.

If you are so dead set against ventilating a property Aron, can I ask firstly what are your suggestions on how to resolve it , using the tools at hand, How can a homeowner with so called ' inferior ' windows eleiminate the condensation?

Then can I draw you to a comment you made yourself , another post on this very forum , not a week ago.

, so you need to lower the humidity levels, can be done by further ventilation, lots of topics on this so search the forum.

This one statement is what every other person has been saying and yet you have come on here and said that everyone of us is hung up on ventilation...well I am not too sure what to think about your complete contradiction....................

 

[typonaut]

The issue is to do with peaks of humidity levels....can't you see that! If you have extra water vapour being added to the building through bathing etc...where does it go?
Condensation Physics in a nutshell, are warm moist air settling on cold surfaces , forming water droplets. So to you average conditions are when nobody is doing anything in the property, to completely ignore bathing, cooking 'peaks ' etc is very shortsighted

This is a complete mischaracterisation of how condensation can and does form. It may be the case that peak humidity does cause condensation, and then this disperses, or can disperse, through ventilation.

But, condensation can also form in a room where the average humidity is in the "normal" range - ie 30-55%. This is due to localised cooling, not because the humidity in the room is too high.

As I demonstrated above, the temperature in the centre of a room could be 21°, but at a window sill it can be 16°. That temperature drop in itself takes 50% humidity in the middle of the room to around 75% at the window sill. I think we can also assume that the actual temperature at the aluminium frame is somewhat below that of the air close to the frame, so increases humidity yet further (not to condensation point on that particular day, but one should be able to understand how that could be achieved).

What you'll note from above is that there was only 2° difference between the window sill and external temperature. I did that experiment in the morning, which may account for that small change. Late this afternoon the room temperature is again 21°, the sill is 18° and the external temp is 12. So there is probably something to be said about the peak condensation point being early in the morning.

 

[ronniecabers]

The issue is to do with peaks of humidity levels....can't you see that! If you have extra water vapour being added to the building through bathing etc...where does it go?
Condensation Physics in a nutshell, are warm moist air settling on cold surfaces , forming water droplets. So to you average conditions are when nobody is doing anything in the property, to completely ignore bathing, cooking 'peaks ' etc is very shortsighted

This is a complete mischaracterisation of how condensation can and does form. It may be the case that peak humidity does cause condensation, and then this disperses, or can disperse, through ventilation.

But, condensation can also form in a room where the average humidity is in the "normal" range - ie 30-55%. This is due to localised cooling, not because the humidity in the room is too high.

As I demonstrated above, the temperature in the centre of a room could be 21°, but at a window sill it can be 16°. That temperature drop in itself takes 50% humidity in the middle of the room to around 75% at the window sill. I think we can also assume that the actual temperature at the aluminium frame is somewhat below that of the air close to the frame, so increases humidity yet further (not to condensation point on that particular day, but one should be able to understand how that could be achieved).

What you'll note from above is that there was only 2° difference between the window sill and external temperature. I did that experiment in the morning, which may account for that small change. Late this afternoon the room temperature is again 21°, the sill is 18° and the external temp is 12. So there is probably something to be said about the peak condensation point being early in the morning.

Condensation is caused when water vapour comes into contact with cold surfaces and condenses to form dampness or water droplets. Air can contain varying amounts of water vapour; warm air can hold more water vapour than cold air.
Condensation in homes - NHBC Home
www.nhbc.co.uk/NHBCPublications/.../filedownload,31929,en.pdf

peak condensation in your house , as all houses are different, could well be due to the lack of air movement in that particular room , as most ( admittedly not all ) people are asleep overnight and not moving....

 

[typonaut]

In fact their windows are generally so much better, that the problem of external condensation is more widely known and understood…

I had to think about that for a moment - how could you get external condensation!? So, I figure that this is most likely to happen early in the day, the external glazing has cooled overnight, the external air is warming up and increasing its moisture capacity, but comes into contact with the cooler glazing (which is warming more slowly than the air, and isn't being warmed from internal sources because it is more efficiently insulated).

Would that be the scenario?