I know it has been discussed before, but I still feel a bit uncertain regarding the function of the vapor barrier in the walls. As far as I understand, it is supposed to prevent moisture from the indoor air from being pushed into the insulation. But I experience a large negative pressure in the house as air is actually being sucked into the house, and therefore the risk of moisture being pushed into the insulation should be very small. Or am I missing something here?
I can imagine that the vapor barrier serves a more important function in the ceiling as warm air, which contains more moisture, tends to rise and settle in the ceiling. Is this correct?
Best regards,
David
I can imagine that the vapor barrier serves a more important function in the ceiling as warm air, which contains more moisture, tends to rise and settle in the ceiling. Is this correct?
Best regards,
David
At the risk of being inaccurate, I have the impression that it has to do with vapor pressure rather than air pressure.
Nature tends to equalize things, warm indoor air is more humid than cold outdoor air, and thus the higher vapor pressure indoors wants to push out through the walls/ceiling. If there is no vapor barrier, the moisture condenses on its way out through the insulation, which can result in mold damage.
Nature tends to equalize things, warm indoor air is more humid than cold outdoor air, and thus the higher vapor pressure indoors wants to push out through the walls/ceiling. If there is no vapor barrier, the moisture condenses on its way out through the insulation, which can result in mold damage.
In my strange world, this reasoning makes sense...
Therefore, one should not have a vapor barrier in houses where there is a risk that it is colder inside the house than outside, because then the moisture stays on the wrong side of the vapor barrier.
Applicable to, for example, summer cottages...
Therefore, one should not have a vapor barrier in houses where there is a risk that it is colder inside the house than outside, because then the moisture stays on the wrong side of the vapor barrier.
Applicable to, for example, summer cottages...
But is there any example (pictures or someone who has seen for themselves) of it becoming so humid in an exterior wall that it starts to mold and rot in a regular residence, not a bathroom wall though........hmmmmm
Maybe there's a bigger risk if you've painted with some dense paint on the outside, acrylic for instance!
What about Demidekk's paint, I think it's called "polyacrylate," is it also completely dense?
Is it important to install panels painted with acrylic/polyacrylate with an air gap?
Maybe there's a bigger risk if you've painted with some dense paint on the outside, acrylic for instance!
What about Demidekk's paint, I think it's called "polyacrylate," is it also completely dense?
Is it important to install panels painted with acrylic/polyacrylate with an air gap?
It has to do with condensation. Warm air can carry more water molecules per cubic meter than cold air. Therefore, water condenses where the warm air meets the cold air, in walls and ceilings. The vapor barrier prevents this from happening inside the wall and thus making the studs and insulation wet. Wet studs lead to mold growth. If, against all odds, it does get wet, it must be ventilated away - hence the air gap.
That is precisely why you shouldn't have a vapor barrier in houses that are only heated part of the year - the water condenses on the wrong side of the vapor barrier.
The vapor barrier should always be on the warm side. Nowadays, 45 mm insulation is put in and then the vapor barrier - this is done to be able to run electricity, etc., without penetrating the vapor barrier.
That is precisely why you shouldn't have a vapor barrier in houses that are only heated part of the year - the water condenses on the wrong side of the vapor barrier.
The vapor barrier should always be on the warm side. Nowadays, 45 mm insulation is put in and then the vapor barrier - this is done to be able to run electricity, etc., without penetrating the vapor barrier.
According to my drawings, the vapor barrier should be laid with at least 600 mm overlap...
I have a vapor barrier in the floor/ceiling between the floors. Feels a bit overkill if you read the reasoning above since there is no warm vs. cold side. Maybe even a little harmful?
I have a vapor barrier in the floor/ceiling between the floors. Feels a bit overkill if you read the reasoning above since there is no warm vs. cold side. Maybe even a little harmful?
We have a so-called kombiväv in the floor structures and ceiling, it serves as both a breakthrough protection and vapor barrier. In the intermediate floors with warmth on both sides, this fabric should be punctured so that a seal is not created.
We have the same fabric in the ceiling against the insulation there; the supplier probably thought it was easiest to use the same everywhere.
For the outer roof, breakthrough protection is not really needed, and indoors the vapor barrier is not necessary.
We have the same fabric in the ceiling against the insulation there; the supplier probably thought it was easiest to use the same everywhere.
For the outer roof, breakthrough protection is not really needed, and indoors the vapor barrier is not necessary.
Regarding moisture barrier in the ceiling above a wet area: isn't that exactly what the interior moisture barrier is for? To prevent moisture from migrating inside the walls/ceiling/floor?
I have another question: we are going to insulate the storage. It will not be heated at all, we are only aiming for slightly less temperature fluctuations inside. Should there be any moisture barrier then? According to the reasoning above (which I agree with, by the way), the moisture barrier should be on BOTH sides of the insulation. Or maybe the temperature difference won't be big enough for condensation to form on the walls? Then maybe it's not worth insulating at all? What we would like is about a 5-degree difference compared to the outside temperature.
C
I have another question: we are going to insulate the storage. It will not be heated at all, we are only aiming for slightly less temperature fluctuations inside. Should there be any moisture barrier then? According to the reasoning above (which I agree with, by the way), the moisture barrier should be on BOTH sides of the insulation. Or maybe the temperature difference won't be big enough for condensation to form on the walls? Then maybe it's not worth insulating at all? What we would like is about a 5-degree difference compared to the outside temperature.
C
OK, let me clarify a bit.
In the attic floor (or whatever it may be called), you need a vapor barrier to prevent moisture from entering the insulation between the warm indoor air and the cold outdoor air in the cold attic. We don't have much space to speak of up there, maybe 0.5 m between the top of the insulation and the roof ridge, so we will never be climbing around up there. The anti-fall protection is (I believe) a work safety feature that means you should set it up at an early stage in construction as a protection against falling through the floor before the flooring is installed. It can therefore be useful for the ground and intermediate floors, but hardly for an attic space where no one will ever climb around.
Similarly, as far as I understand, you should not have a vapor barrier in intermediate floors.
With the type of combined anti-fall protection/vapor barrier mat that we have, you therefore get the anti-fall protection as a bonus in the attic floor, but it should/must be perforated in the intermediate floors to remove the vapor barrier function.
It looks like a transparent reinforced tarp, very tough and strong.
In the attic floor (or whatever it may be called), you need a vapor barrier to prevent moisture from entering the insulation between the warm indoor air and the cold outdoor air in the cold attic. We don't have much space to speak of up there, maybe 0.5 m between the top of the insulation and the roof ridge, so we will never be climbing around up there. The anti-fall protection is (I believe) a work safety feature that means you should set it up at an early stage in construction as a protection against falling through the floor before the flooring is installed. It can therefore be useful for the ground and intermediate floors, but hardly for an attic space where no one will ever climb around.
Similarly, as far as I understand, you should not have a vapor barrier in intermediate floors.
With the type of combined anti-fall protection/vapor barrier mat that we have, you therefore get the anti-fall protection as a bonus in the attic floor, but it should/must be perforated in the intermediate floors to remove the vapor barrier function.
It looks like a transparent reinforced tarp, very tough and strong.
I read this discussion with interest and wonder if the reasoning can also be applied one floor down, i.e., to a wooden floor over a crawl space foundation?
I wonder if it is suitable, or directly unsuitable, to put a vapor barrier under the chipboard in the floor joists (wood) to stop moisture migration from the foundation? We intend to lay engineered hardwood on the floor.
With my somewhat limited knowledge, it sounds like the moisture condenses in the floor structure, which can lead to mold/rot.
/zeluf
I wonder if it is suitable, or directly unsuitable, to put a vapor barrier under the chipboard in the floor joists (wood) to stop moisture migration from the foundation? We intend to lay engineered hardwood on the floor.
With my somewhat limited knowledge, it sounds like the moisture condenses in the floor structure, which can lead to mold/rot.
/zeluf