The vapor barrier..Is it proven ??

[Mikael_L]

I agree with you 100% in the first half of your long post.

Then when you get to the "fantastic" cellulose insulation, I have a few comments.
(No serious dispute )
But now I'm a bit short on time, I'll try to get back to it this evening.

I am an educated building engineer (In Finland, this means a 4-5 year engineering education after a 2-3 year vocational school or matriculation exam). I took all the voluntary courses in heat and moisture physics and have always been interested in the area even though I haven't directly worked with it.

This is how I've understood the problem:
In warm air, the vapor pressure is much greater at the same relative humidity as in cold air. This means that moisture migrates from warm to cold. Even when the relative humidity is higher on the cold side.
Inside a modern house, there are many moisture sources. We humans evaporate moisture and we cook, shower, and dry clothes. All that moisture wants to seek its way out through the walls and roof.
The underlying physics with vapor contents and vapor pressure at the molecular level can be somewhat understood..... but I can't explain it in a hurry like this, so can we accept the phenomenon?

The dew point in a construction is the point where the temperature has dropped so low that the indoor air can no longer hold the given moisture amount in gas form, so some of the moisture precipitates as liquid water.
In all insulated buildings, the dew point will be within the construction for a significant part of the year. The thicker the insulation, the further inside the structure the dew point lies during the major part of the year.
Rock wool and glass wool are mineral materials. This means they do not contain hygroscopic (moisture-absorbing) cell structures with the ability to absorb water and transport it further. This means that moisture that condenses at the dew point in a construction with these cheap insulation materials cannot be transported to the surface and dried. It results in the moisture being retained and accumulating inside the structure.
To prevent this, the inside is lined with plastic. Theoretically, it's a perfectly ideal solution that entirely prevents any moisture from reaching the dew point. Practically, everyone who has ever worked in construction and renovations knows that the plastic is always full of holes and that tapes and sealants come loose over time. The plastic itself seems to age and connections and corners are very rarely tight.
That's why we get sick buildings, more or less. A well-made moisture barrier reduces the risk, but the risk is always there. Especially in today's super-insulated houses.

Cellulose-based insulation has the ability to absorb water. Since the moisture content in a hygroscopic material always strives to even out, some of the moisture will always be transported to the surface and evaporate. Gradually, the moisture dries out.
That's why one can manage without a vapor barrier in such constructions. The interior boards and some paper that slows most of it down are sufficient. In such moisture-permeable construction, it is important that the exterior is as permeable to moisture as possible. Windshield gypsum is, in other words, totally banned. Porous wood fiber-based wind protection boards have greater moisture permeability and better lambda value. This means less condensation on the inside and also that the condensation moisture that still occurs finds it easier to travel to the surface and evaporate.

My personal opinion is that today's super-insulated houses are a dead end. Especially the standards that apply in Finland.
With these enormous insulation thicknesses (25 cm in walls and 45-50 cm in roofs), it is impossible to build moisture-safely. Until someone presents a better solution, I believe we will be forced to compromise on insulation requirements in the future simply because no human society can afford to tear down and renew all houses at 30-40 year intervals.
If at the same time one thinks a bit about how to design the house to avoid window walls, unnecessary exterior doors, and patio doors without vestibules and other completely insane solutions and settles for slightly fewer heated square meters, it is possible to achieve reasonable energy consumption also with slightly thinner insulation.

 

[Mikael_L]

I completely agree with the last part. The moisture is 100% dependent on the temperature difference, the heat is directly crucial for the issue since the heat goes through all materials, one cannot solve moisture migration just by fixing the houses

I understood nada from this post ... ?

But that heat goes through all materials doesn't mean moisture goes through all materials, they are very different physical things. But the two affect each other.

 

[Mikael_L]

the wallpaper paste found in most properties is diffusion tight,

No. It is generally extremely diffusion open.

heat is not a particle but a wave, which means that physics is obsolete in the usual way and transitions to radiation that does not follow a fixed particle's behavior.

Heat is atomic and subatomic movement in material. Heat radiation is electromagnetic radiation. Heat is also transferred through conduction, not just radiation. Yes, even through convection of various types. Physics is absolutely not obsolete. On the contrary, if you really want to understand the mechanisms, a good basic physical intuition and knowledge are valuable.

so there is much we don't know when it comes to how moisture arises, how it behaves in different materials, etc.

We know an extreme amount about this. We have slightly less knowledge about how it interacts in mixtures of materials. We have the least knowledge about how theory stands in practice, when careless builders neglect to tape joints or seal all parts, or when there are double tight layers in various places, etc. It is, therefore, the construction phase that is the biggest problem.

In my opinion, the heat goes through the vapor barrier and causes the cooler air to precipitate its water vapor due to a collision between warm and cold air, and this results in condensation in the insulation,

You've written this wrong, but I think you're thinking correctly. The warm and humid air passes through the wall construction, i.e., when the vapor barrier is missing, and there, in a colder section of the wall, the water is precipitated. This is evidence that the vapor barrier "is necessary."

Hammarby sjöstad is proof of this, the million program is another, newly built villas with similar issues, newly built multi-family houses with single-step facades (ok, another type of problem) the list could be made as long as possible.

Hammarby sjöstad was a catastrophic build primarily because too much moisture was built into the construction process itself. It was allowed to rain on building materials that were then built in, no concrete structures were allowed to dry out sufficiently, etc. A really worthless project that should have received some sort of reverse Nobel Prize for worst executed contract. Single-step sealed facades have mainly the problem that a very diffusion-resistant layer has been placed on the exterior, instead of closest to the warm side of the wall. Much like placing the vapor barrier on the outside of the house instead of the inside. Foolish, simply put. Moreover, all knowledgeable people already knew this beforehand, but money in the companies' pockets was a stronger argument.

But I didn't start this thread to get help with things I already know but to get scientific evidence, and there's no one who has been able to upload such or send it to me... therefore a vapor barrier is a joke and a false pretense. If I'm wrong, send me a document from KTH, Chalmers, or Gävle or Örebro universities. Then I'll believe it’s beneficial; otherwise, it's a lie.

You've received some links in the thread. Do you bother to read them? There are many studies done by SP, universities, Boverket, etc. Then you could also take and learn basic physics, and then you can also figure out that it’s correct.

There are two camps here. Those who know physics, calculate the whole thing, who conduct controlled studies, and/or check and trust other such studies.

The other camp consists of people who don't know a lick of physics, who never believe in what has been scientifically concluded. These people also usually trust heavily in the outcome of a single incident ("My grandmother's house is 200 years old and still perfectly sound, without a single piece of plastic there") but disregard large studies that involve larger quantities of researched objects, or controlled studies. It's like saying that just because a relative won on a scratch-off, it would mean everyone wins, if they're just smart enough to buy a scratch-off.