The vapor barrier..Is it proven ??

[Ribons]

Yes, if it's set up that way, the vapor barrier won't handle it either (moisture/water behind the boards). Obviously, no one is reacting to the wallpaper paste in my arguments; if you have a layer that is diffusion-tight, then the moisture can't be transported through it... right? And then the vapor barrier is just a thing that serves no purpose, right? And if now the moisture can pass through all 6 layers before the vapor barrier completely unaffected, there should be an inland lake behind the boards. And then the insulation should be dry to at least 75% of it. right? But according to the measurements I've participated in (with a moisture meter that measures 100mm into the way showed that it should have been dry in the middle of the insulation, right?) but no, the moisture content was extremely high for certain properties on the facades I measured. (For a light concrete wall, the moisture content should be between 30-36 in moisture content (this is the material's own moisture that it has in its nature as they say), but the content has in some cases been up to 50-80 in moisture content, which is extremely high (not the worst I've seen). These properties are in the Million Program, and it differs a bit between the different directions, but are quite normal moisture values. Concrete has lower, about 5-10 in content, wood should have 8-12 to feel good, and light concrete 30-35. Some values for those of you who know.

...but lots of people HAVE problems with moisture and mold, so it's not working in practice...

But your question is if it works in theory. And I think it does. It would surprise me if there wasn't a scientifically written document explaining how the plastic film is supposed to work.

It's important to distinguish between theory and practice!

That your house works without foil can be due to many things, including ventilation and how much moisture load you give it. I'm quite sure you can create a climate that will cause almost any house to become moisture damaged. Max heat, full shower and water boiling, and no ventilation. Build a little Japanese indoor spa in the living room where you serve freshly cooked rice to 20 sweaty sauna-bathing sumo wrestlers and you'll see that none of the building methods we've discussed can prevent moisture damage... Now it's Friday!

 

[Ribons]

v not if you've missed my question? but I wanted to have proof (scientific comparison between two different construction methods and get the vapor barrier proven) I don't need to prove anything just because I have a question, right?

 

[JohanLun]

v didn't know if you missed my question? but I wanted evidence (scientific between two different construction methods put against each other and get the vapor barrier proven) I don't need to prove anything just because I have a question or do I?

But... what you're saying is that you have a vapor barrier in the form of wallpapers and boards, so really no one disputes that something should prevent moist air from penetrating and condensing in the walls. You agree with that, right?

The discussion about material choice is another matter, and there I believe more of us agree with you that plastic, as it's installed today, often has a poorer function than intended (and maybe is saved by walls, etc. helping out...).

 

[Marlen Eskilsson]

I have deleted inappropriate posts and personal attacks. A post should drive the discussion forward.

/Moderator

 

[heimlaga]

I am a trained civil engineer (In Finland, this means a 4-5 year engineering education after 2-3 years of vocational school or high school diploma). I attended all optional courses in heat and moisture physics and have always been interested in the field even though I haven't worked with it directly.

This is how I understand the issue:
In warm air, the vapor pressure is considerably higher at the same relative humidity as in cold air. This means that moisture moves from warm to cold. Also when the relative humidity is higher on the cold side.
Indoors in a modern house, there are many sources of moisture. We humans evaporate moisture and we cook, shower, and dry clothes. All that moisture wants to move out through the walls and roof.
The underlying physics with vapor content and vapor pressure at the molecular level can be understood reasonably..... but I can't explain it hastily like this, so can we just 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 amount of moisture in the gas form, so some of the moisture falls out as liquid water.
In all insulated buildings, the dew point will be inside the construction for a significant part of the year. The thicker the insulation, the further in the dew point lies during a larger part of the year.
Stone wool and glass wool are mineral-based 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 insulating materials cannot be carried out to the surface and dry. This means the moisture hangs and collects inside the construction.
To prevent this, you cover the inside with plastic. Theoretically, it is a perfectly perfect solution that completely prevents all moisture from reaching the dew point. Practically, anyone who has ever worked on construction and renovations knows that the plastic is always full of holes and that tape and sealants give way over time. The plastic itself seems to age, and connections and corners are 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. Because the amount of moisture in a hygroscopic material always strives to even out, some of the moisture will always be transported out to the surface and evaporate. Gradually, the moisture dries away.
Therefore, a moisture barrier is not needed in such constructions. Interior boards and some paper that blocks most of it is enough. In such a moisture-permeable construction, it is important that the exterior is as moisture-permeable as possible. Wind protection gypsum is, therefore, 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 that the condensation moisture that does occur can more easily travel to the surface and evaporate.

My personal opinion is that today's super-insulated houses are a dead end. Particularly the standards that apply in Finland.
With such enormous insulation thicknesses (25 cm in walls and 45-50 cm in roofs), it is not possible to build moisture-securely. Until someone presents a better solution, I believe we will have to compromise on insulation requirements in the future simply because no human society can afford to demolish and renew all houses at 30-40 year intervals.
If at the same time you think a little about how you design the house so you avoid window walls and unnecessary exterior doors and patio doors without vestibules and other completely insane solutions and settle for slightly fewer heated square meters, you can achieve a reasonable energy consumption even with slightly thinner insulation.

 

[Ribons]

Question:
1. Is the wallpaper adhesive vapor proof?
2. If I have 100ml of water vapor on the inside-->how much goes through the wallpaper.wallpaper adhesive:cardboardlaster 13mm: OSB board 13mm how many ml go through?
why do we have the problems we have if airtight houses are so good?=?

I am a trained civil engineer (In Finland, this involves 4-5 years of engineering education after 2-3 years of vocational school or high school diploma). 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.

Here's how I've understood the issue:
In warm air, the vapor pressure is extraordinarily much greater at the same relative humidity as in cold air. This means that moisture migrates from warm to cold. Also when the relative humidity is higher on the cold side.
Indoors in a modern house, there are many sources of moisture. We humans evaporate moisture, and we cook, shower, and dry clothes. All that moisture wants to escape through the walls and ceiling.
The underlying physics with vapor amounts and vapor pressure at the molecular level can be somewhat understood..... but I can't explain it hastily like this so can we accept the phenomenon?

The dew point in a structure indicates the point where the temperature has dropped so low that the indoor air can no longer hold the given amount of moisture in gas form, so some of the moisture falls out as liquid water.
In all insulated buildings, the dew point will be inside the construction for a significant part of the year. The thicker the insulation, the further inside the dew point is for a larger part of the year.
Rock wool and fiberglass are mineral materials. This means they do not contain hygroscopic (moisture-absorbing) cell structures capable of absorbing water and transporting it. This means that moisture that condenses at the dew point in a construction with these cheap insulation materials cannot be led out to the surface and dry. This means that moisture remains suspended and accumulates inside the structure.
To prevent this, the inside is lined with plastic. Theoretically, it's a perfectly perfect solution that completely prevents any moisture from reaching the dew point. Practically, everyone who has ever worked on construction and renovations knows that the plastic is always full of holes and that tape and caulking release over time. The plastic itself seems to age, and connections and corners are rarely tight.
That's why we get sick buildings. More or less. A well-made vapor 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 amount of moisture in a hygroscopic material always strives to even out, some of the moisture will always be led to the surface and evaporate. Gradually, the moisture dries away.
Therefore, one can do without a vapor barrier in such constructions. The interior boards and some paper that stops most of it are sufficient. In such a moisture-permeable structure, it is important that the outside is as moisture-permeable as possible. Gypsum wind barriers are, in other words, totally banned. Porous wood fiber-based wind barrier boards have greater moisture permeability and better lambda value. This means, among other things, less condensation on the inside and also that the condensation moisture that still occurs can more easily migrate 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 such enormous insulation thicknesses (25 cm in walls and 45-50 cm in the roof), it's not possible to build moisture-proof. Until someone presents a better solution, I think we will have to compromise on insulation requirements in the future simply because no human society can afford to demolish and renew all houses every 30-40 years.
If at the same time you think a little about how to design the house to avoid window walls and unnecessary exterior doors and patio doors without vestibules and other completely insane solutions and settle for slightly fewer heated square meters, it is possible to get a reasonable energy consumption even with slightly thinner insulation.

 

[Freddedan]

In my opinion the heat goes through the vapor barrier and causes the cooler air to release its moisture

Warm air can contain a lot of moisture.
Cold air can contain little moisture.

With a vapor barrier, you want to prevent moisture from following warm air into the insulation where the air is cooled and has to get rid of moisture, which happens by the moisture being released as water droplets - condensation.

 

[Ribons]

Heat waves cannot carry anything; they are a wave equivalent to a sound wave. Heat is NOT a particle but a wave motion. It passes straight through the vapor barrier and the wall and everything in its path "conductive heat."

Warm air can contain a lot of water vapor.
Cold air can contain little water vapor.

With a vapor barrier, you want to prevent water vapor from following warm air into the insulation where the air cools down and has to get rid of water vapor, which occurs by the water vapor being precipitated into water droplets - condensation.

 

[Ribons]

There are no studies on how moisture is transported through, let's say, 2mm paper wallpaper, 1mm wallpaper paste, 2mm cardboard, 13mm gypsum, 2mm cardboard, 13mm OSB board, and then on the other side, the water vapor should completely untouched by these barriers get stuck in the vapor barrier, thereby saving the wall from a certain moisture damage. Does this sound like a likely theory?

 

[Ribons]

If you want to prove something, you have to conduct extensive studies with every single house type and construction, and that price increase is not of interest, so that's why building is done according to general standards.
It requires rigorous tests and calculations to determine whether that particular house needs a vapor barrier or not, and as mentioned, it is simpler to build with it in everything.

It is not a new construction that I am thinking about, but rather a detail that has been on the market for about 30-40 years, so if there is evidence that houses should have a vapor barrier to avoid moisture damage, this should have been available for a long time.

 

[Isakare]

An acquaintance of mine has no plastic in his house built 15 years ago with thick walls and modern materials. He sealed all gaps at the ceiling and floor after the drywall with latex sealant, filled them as usual, and carefully painted all the walls and ceilings with 3 coats of paint. The paint (latex) is the moisture barrier, according to him who is a carpenter, it's an approved method, and the moisture barrier is placed where it does the most good.

 

[Ribons]

also an alternative

 

[JohanLun]

it is not a new construction that I am considering, but a detail that has been on the market for about 30-40 years, so if there is evidence that can show that houses should have a vapor barrier to avoid moisture damage. this should have existed for a long time

I think Heimlaga's post was very well written. It shows that plastic sheeting does not solve all the world's problems, but it exists for a purpose. That there are other methods that are both better and worse does not mean that the plastic film has no justification. Just because metal roofing works, does not mean that tile roofing does NOT work.

I also found the links below to read;
https://www.sp.se/sv/index/services/moist/general/Sidor/default.aspx
http://www.thermocell.se/produktinfo/tathet_diff.htm

Maybe the links at SP lead to some test results? Haven't had the time / energy to read through them.

The links above mention that properly installed double plasterboard provides roughly the same convection tightness as a plastic film, which would support your empirical result that it works well without the plastic. But that does not mean it has no function. What I particularly wonder about is how tight, for example, the holes around the electrical boxes are? But if you apply sealant around all these holes, it should become airtight. Likewise, the corners, if you place a metal profile between the OSB and plasterboard in the corners, it should stop the airflow there.

I have at least chosen to place isolinas paper and carefully ensure to seal all places where air might pass.

To prevent diffusion (the difference in vapor content between inside and outside), a so-called vapor barrier, in the form of plastic sheeting, is usually placed on the inside (warm side) of the climate shield, where the vapor content is usually highest. This way, the water vapor is prevented from diffusing through the climate shield.
To prevent moisture convection (the difference in air pressure between inside and outside), the climate shield must be as airtight as possible. If you also have plastic sheeting there, it serves as both a vapor barrier and an air barrier.
From an air tightness perspective, and thus from a moisture convection perspective, the airtight layer does not need to be vapor-tight and can thus consist of materials that are not vapor-tight.

In summary, the primary role of plastic sheeting is to protect mineral wool/synthetic materials, which are open to air movement and cannot handle moisture convection. Frost and condensation form in the mineral wool when the air is humid and the temperature is sufficiently low on either side of the insulation material.

Over the last few decades, plastic sheeting has been used for airtightness and vapor tightness in framework constructions in traditional building. The reason for using plastic sheeting was that building codes since 1967 have required high vapor tightness on the inside of exterior walls and roofs, for example, the requirement in SBN 75 was that the inner barrier should be five times tighter than the outer one in walls, and ten times tighter in roofs.

So having an airtight house is self-evident and has nothing to do with the vapor barrier function.
Good air tightness is a prerequisite for controlled ventilation and good energy efficiency.
If a construction does not have sufficient air tightness, air will leak in and out uncontrollably through gaps. If you do not want plastic sheeting as the inner barrier, the air tightness must be arranged with other materials or in other ways.

The vapor content of indoor air in common buildings usually does not cause damage in exterior walls. The need for a vapor barrier in a wall is therefore small, at least in well-ventilated buildings, like offices, schools, and apartments in modern multi-family houses, where the vapor surplus in indoor air is low, usually just a few grams per cubic meter. More important is that there is no tight layer in the colder part of the wall.

Moisture damage in exterior walls is usually caused by water vapor from indoor air that follows outward air currents, often in the upper part of the walls, by rain penetrating the facade, and by construction moisture.

SP in tightness testing has shown that it doesn't greatly matter which barrier is used, i.e. plasterboard, plastic sheeting, or "windtight".

Air leaks to attic floors were at 50Pa
- for double gypsum = 0.37
- for windtight & gypsum = 0.53
- for plastic sheeting & gypsum = 0.40

-Solutions with double gypsum supplemented with fiber cloth at connections give roughly the same result as solutions with plastic sheeting.
-Solutions with single gypsum and spackled seams give the same result as corresponding solution with plastic sheeting.

According to BBR 94, the requirements for air tightness were 0.8 liters/(sm2) or 2.9m3(m2h) at 50 Pa pressure difference. This was later changed in BBR 96 to 0.6 liters/(sm2).
Now the numerical value for the maximum allowable air leak over the climate shield at 50 Pa pressure difference has been removed. In the new building regulations, it can still be stated that in the future, to fulfill the functions in the building regulations, we are required to build significantly tighter houses than today. The advisory text in the building regulations moisture section about achieving "as good air tightness as possible" should not be underestimated.

SP has in another study "Torra tak" compared mineral wool insulation with cellulose insulation in unventilated parallel roofs. The most favorable version turned out to be those with cellulose.
The pockets had a thickness of 290 mm and a density of 46-63 kg/m3.
The airflow at 50 Pa was for cellulose 1.21 while the mineral wool had 2.33.

So, almost twice as high airflow for mineral wool at the same density.
(Note that mineral wool boards in reality barely have half the density).

In mechanically ventilated houses with plastic sheeting, the relative humidity indoors is reduced to too low levels. The moisture is led away with the ventilation air, while the plastic sheeting prevents the airing out of any moisture in the construction, with a risk of moisture damage and increased emissions from building materials. Houses built with wood fibers and without vapor barriers, plastic wallpapers, or plastic paints, provide a more pleasant indoor climate. The diffusion openness allows an airing out of the construction that is necessary to prevent moisture damage. In addition, the wood fiber insulation's ability to absorb moisture helps to lower the moisture content in other construction parts. The indoor climate becomes favorable for humans. Favorable regarding indoor relative humidity, which stabilizes within the right range (40-60%), thanks to the diffusion-open construction and wood fiber insulation's ability to equalize moisture.

According to Dalton's law, individual gases communicate. If the oxygen level is low inside, oxygen strives to enter through the construction (it is aired in), and the oxygen level inside becomes in equilibrium with the oxygen level outside. In a similar way, the excess of carbon dioxide is pressed out through the construction, "it is aired out". The diffusion openness gives nature a "fair chance" to act.

Air tightness, as previously mentioned, has great significance for moisture safety. In cases where there is an internal overpressure, while the indoor air has a moisture surplus, moist air will flow out through gaps in the building envelope. The outer structure is thus supplied with moisture and the risk is high that the relative humidity becomes high enough for mold to grow on materials with low mold resistance.

 

[vectrex]

A fundamental error that seems quite prevalent in this thread is the (mis)understanding of the difference between convection and diffusion.

That something is airtight does not mean it is diffusion-tight. Nothing is diffusion-tight, it is just more or less diffusely open!

 

[Ribons]

don't really know how to phrase myself to make you understand what I mean... NOW I'M LOOKING AT A COMPLETELY NORMAL WALL AND HOW IT'S BUILT IN AN APT OR A HOUSE, IN ANY ROOM EXCEPT NOT IN THE BASEMENT!!!!
Structure of a regular apt wall=Wallpaper-->Wallpaper Paste--> Cardboard (the top of the plasterboard is covered in cardboard-like material)-->pure top compressed gypsum-->another cardboard sheet on the underside of the gypsum-->OSB board or chipboard. Determine how much moisture can pass through all these 6 layers with resistance with normal air pressure in a completely normal apt on a completely normal Monday or any other day of the week.
Have you understood??
I'm guessing the paste is dense and doesn't let any moisture through at all.