During our 1.5-year renovation period, I've probably asked 4000 questions to friends, acquaintances, carpenters, masons, roofers, etc., you know how it is... However, I've noticed that few things make those knowledgeable in the field more engaged than when you bring up the question of whether to have plastic on the inside of exterior walls or if it should be wind barrier.
Both camps are equally convinced that one means the death of the house and the other is the only right choice:
"The plastic prevents the house from breathing and therefore is not good for either you or the house, so the only right choice is only wind barrier."
"Without plastic, the warm air from inside will go out into the wall and condense against the cooler air inside the wall."
At the County Administrative Board's construction consultations and in building stores, there doesn't even seem to be an alternative to plastic. Even though it's actually the most experienced carpenters who say that plastic is crap...
In the middle, there's me, not knowing which way to turn. What do you think? Bombard me with opinions!!!
Both camps are equally convinced that one means the death of the house and the other is the only right choice:
"The plastic prevents the house from breathing and therefore is not good for either you or the house, so the only right choice is only wind barrier."
"Without plastic, the warm air from inside will go out into the wall and condense against the cooler air inside the wall."
At the County Administrative Board's construction consultations and in building stores, there doesn't even seem to be an alternative to plastic. Even though it's actually the most experienced carpenters who say that plastic is crap...
In the middle, there's me, not knowing which way to turn. What do you think? Bombard me with opinions!!!
why would plastic be bad? However, if you have an old house like I do, you need to adjust the ventilation to ensure a good climate, but this also applies when replacing windows etc... for houses with natural ventilation....
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There actually exists a new "vindpapp" that is plastic-like with some kind of fabric on it (a bit hard to describe). It is at least lightweight, allows moisture to pass through but NOT wind, meaning the house can breathe but not gasp. Much more convenient than the vindpapp, which easily tears when mishandled. This one is more elastic.
I have also thought about the same question and concluded that the situation you describe is entirely true… so to the answer to your question! I am not an expert but can only provide the information that I have received and interpreted myself.
1. In new well-insulated houses, plastic should always be used because the dew point ends up inside the wall. That is, the air condenses. The wall is not built to absorb moisture without being damaged.
2. In old houses where the entire wall is basically heated and the dew point ends up on the outside, there is less or no condensation in the wall. Moreover, sawdust or other insulation materials that can absorb some moisture during cold periods to then evaporate during warmer periods were often used. However, this is a sensitive balance and can easily be disrupted by additional insulation. Then the dew point comes further into the wall.
3. In summer houses and buildings that stand unheated for parts of the year, plastic should not be used. Because you can get reverse condensation when it is colder inside the house than outside, for example on a warm spring day when the cold from the night lingers in the house.
As I said, there are many opinions. But as I understand it, plastic should always be used as a vapor barrier if you have a well-insulated wall. There are programs and tables to calculate where the dew point will be located, which can be good to know if you're going to add insulation.
Good luck!
1. In new well-insulated houses, plastic should always be used because the dew point ends up inside the wall. That is, the air condenses. The wall is not built to absorb moisture without being damaged.
2. In old houses where the entire wall is basically heated and the dew point ends up on the outside, there is less or no condensation in the wall. Moreover, sawdust or other insulation materials that can absorb some moisture during cold periods to then evaporate during warmer periods were often used. However, this is a sensitive balance and can easily be disrupted by additional insulation. Then the dew point comes further into the wall.
3. In summer houses and buildings that stand unheated for parts of the year, plastic should not be used. Because you can get reverse condensation when it is colder inside the house than outside, for example on a warm spring day when the cold from the night lingers in the house.
As I said, there are many opinions. But as I understand it, plastic should always be used as a vapor barrier if you have a well-insulated wall. There are programs and tables to calculate where the dew point will be located, which can be good to know if you're going to add insulation.
Good luck!
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That concerns two completely different functions within building physics that you need to be aware of when discussing various topics.
Plastic/foil/vapor barrier/UV-stabilized: used to prevent warm and humid indoor air from escaping into the outer wall/attic floor with hygroscopic (water-absorbing) material. Especially the insulation. If the insulation becomes damp, the air content in it decreases, reducing the insulation effect. The zero point in the wall/beam layer (where warm indoor air is cooled to an average of zero degrees as cold outdoor air cools from the outside) then moves towards the inner wall/ceiling, allowing the zero point to continue moving inwards as new and humid air condenses closer to the room side. Therefore, it is essential to have a 'brake' on the moisture to prevent the insulation effect from becoming so poor that it practically becomes nonexistent, leading to mold and rot.
A newer material instead of plastic film exists. It is called a vapor brake. It is not diffusion tight. (I have no experience with this material.)
In combination with a well-functioning and appropriately sized indoor ventilation system (mechanical supply and exhaust with possibly a heat exchanger), a vapor brake might manage to keep the remaining moisture away? This would theoretically mean that the moisture follows the path of least resistance and exits with the air rather than trying to make its way through the wall and end up in the insulation?
Wind barrier paper: used on the exterior of outer walls and on top of insulation against cold attics. It is not diffusion tight (and shouldn't be either). Its task is to stop air movements in the insulation layer. It is not the insulation material itself that insulates, but the air trapped in the insulation material since air is a poor heat conductor. However, if the trapped air is disturbed by free air from outside, the warm air in the insulation material gets mixed and replaced by new cold air. The wall then becomes colder, and more energy is required to heat up the new cold air in the insulation, which is exactly what you want to avoid. Otherwise, you might as well skip the insulation altogether.
__________________
The Builder
Plastic/foil/vapor barrier/UV-stabilized: used to prevent warm and humid indoor air from escaping into the outer wall/attic floor with hygroscopic (water-absorbing) material. Especially the insulation. If the insulation becomes damp, the air content in it decreases, reducing the insulation effect. The zero point in the wall/beam layer (where warm indoor air is cooled to an average of zero degrees as cold outdoor air cools from the outside) then moves towards the inner wall/ceiling, allowing the zero point to continue moving inwards as new and humid air condenses closer to the room side. Therefore, it is essential to have a 'brake' on the moisture to prevent the insulation effect from becoming so poor that it practically becomes nonexistent, leading to mold and rot.
A newer material instead of plastic film exists. It is called a vapor brake. It is not diffusion tight. (I have no experience with this material.)
In combination with a well-functioning and appropriately sized indoor ventilation system (mechanical supply and exhaust with possibly a heat exchanger), a vapor brake might manage to keep the remaining moisture away? This would theoretically mean that the moisture follows the path of least resistance and exits with the air rather than trying to make its way through the wall and end up in the insulation?
Wind barrier paper: used on the exterior of outer walls and on top of insulation against cold attics. It is not diffusion tight (and shouldn't be either). Its task is to stop air movements in the insulation layer. It is not the insulation material itself that insulates, but the air trapped in the insulation material since air is a poor heat conductor. However, if the trapped air is disturbed by free air from outside, the warm air in the insulation material gets mixed and replaced by new cold air. The wall then becomes colder, and more energy is required to heat up the new cold air in the insulation, which is exactly what you want to avoid. Otherwise, you might as well skip the insulation altogether.
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The Builder
This product, which is indeed excellent, should be used on the outside of the wall. It does not replace the vapor barrier installed on the inside of the wall.v-g said:
Read what Byggaren writes above.
One can wonder why so many are fixated on air being able to pass directly through exterior walls (what many call "breathing"). I've never seen anyone perforate a car's body panel to allow the car to "breathe".
The problem is that people do not distinguish what is what, whether the house should have plastic or not is determined by the building materials of the house, etc. The house should "breathe" through a good ventilation system. Mixing different construction techniques with different ventilation techniques is not good.
Here is Mataki's variant of vapor barrier.
Here is Isover's variant.
The central point is that the wind protection on the cold side of the insulation has a vapor diffusion resistance that is 5 times less than that of the vapor barrier, which is on the warm side.
Here is Isover's variant.
The central point is that the wind protection on the cold side of the insulation has a vapor diffusion resistance that is 5 times less than that of the vapor barrier, which is on the warm side.
In this discussion, I can only refer to my own house and its construction, but here the wind barrier is on the inside since the house was built. (Standing 60mm plank with double trätex on the outside)
The new "wind barrier" I've only placed around a window, so its impact is likely marginal but seems to work well anyway since no cold air is coming in
Just wanted to inform you about this nice product!
Cars rarely mold
The new "wind barrier" I've only placed around a window, so its impact is likely marginal but seems to work well anyway since no cold air is coming in
Just wanted to inform you about this nice product!
Cars rarely mold
I had a car that was unregistered at home. It is indeed airtight if it is completely closed. You should have seen how it looked inside. Moldy. Anyway, to the point. If you use some kind of eco-fiber, you don't need plastic. If you have glass wool or stone wool, then you should have plastic. In old houses, it's hard to seal with plastic, so you should use eco-fiber. I myself have two layers of asphalt board, timber, and then two layers of tretex on the inside, with a wood panel with linseed oil paint on the outside. Natural ventilation. Nothing more. No plastics in my house.
It has been said before, but I'll say it again: Fantastic that there is so much knowledge in one forum!!!
Since I'm working on achieving the best possible insulation, primarily with fiberglass insulation, paper is not the option. However, it seems from you that plastic is also not the best, but rather a material that acts as a vapor barrier, e.g., one of the two options Mandus attached.
A follow-up question on this. Let's say I install a vapor barrier. Is it then of utmost importance to attach it as tightly as possible around windows, doors, and at the baseboards and in connection to the ceiling? Or should these areas be "loose"? Our house was renovated in the 1970s, and they did just that. The plastic is not attached at the edges and by the floor and ceiling, so you can feel drafts in certain places...
Since I'm working on achieving the best possible insulation, primarily with fiberglass insulation, paper is not the option. However, it seems from you that plastic is also not the best, but rather a material that acts as a vapor barrier, e.g., one of the two options Mandus attached.
A follow-up question on this. Let's say I install a vapor barrier. Is it then of utmost importance to attach it as tightly as possible around windows, doors, and at the baseboards and in connection to the ceiling? Or should these areas be "loose"? Our house was renovated in the 1970s, and they did just that. The plastic is not attached at the edges and by the floor and ceiling, so you can feel drafts in certain places...
It should be tight. See for example page 9 in Isover's product sheet.
Or Mataki's installation instructions.
Other brands are Windy and Bison. The latter is sold at byggmax.
Or Mataki's installation instructions.
Other brands are Windy and Bison. The latter is sold at byggmax.
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