What governs condensation is the relative humidity and the coldest surface in a room. If the cold surface is so cool that the relative humidity goes over 100% there, then the water condenses until the humidity is lower than that. Simple.
I learned this in middle school in the old laid-back school system of the 70s, staffed with smart, well-educated state-employed adjunct teachers with a real passion for their profession (OT irony
). It was called the law of the cold wall.
If I have read the OP correctly, it's the old hate-insulation found in stud frames from the 40s, 50s, and 60s. It is so vile to work with that I have never seen an example of well-done insulation with such.
If he nails the door hole shut with modern and well-done insulation, it is likely that surface will become the best-insulated exterior wall in the house. Consequently, also the warmest. Plastic then cannot reasonably pose a risk for condensation just there.
Then we can discuss ad nauseam whether it's appropriate for condensation to occur on building plastic or if one should allow moisture to diffuse out through the wall and condense where the sun doesn't shine.
Regardless of where condensation forms, it indicates elevated humidity in the indoor air. Address that first, and it might become another example of why a house without plastic is right. Or proof of why plastic is fantastic and indispensable.
Both are so-called anecdotal evidence that proves nothing until you investigate what has actually gone wrong, or right.
Regards, Findus
I learned this in middle school in the old laid-back school system of the 70s, staffed with smart, well-educated state-employed adjunct teachers with a real passion for their profession (OT irony
). It was called the law of the cold wall.If I have read the OP correctly, it's the old hate-insulation found in stud frames from the 40s, 50s, and 60s. It is so vile to work with that I have never seen an example of well-done insulation with such.
If he nails the door hole shut with modern and well-done insulation, it is likely that surface will become the best-insulated exterior wall in the house. Consequently, also the warmest. Plastic then cannot reasonably pose a risk for condensation just there.
Then we can discuss ad nauseam whether it's appropriate for condensation to occur on building plastic or if one should allow moisture to diffuse out through the wall and condense where the sun doesn't shine.
Regardless of where condensation forms, it indicates elevated humidity in the indoor air. Address that first, and it might become another example of why a house without plastic is right. Or proof of why plastic is fantastic and indispensable.
Both are so-called anecdotal evidence that proves nothing until you investigate what has actually gone wrong, or right.
Regards, Findus
??
Absolutely right, I'm still pondering how I should formulate my response in a simple way.findus42 said:
What controls condensation is the relative humidity and the coldest surface in a room. If the cold surface is so cool that the relative humidity exceeds 100% there, then the water condenses until the humidity is lower than that. Simple.
I learned this in high school in the old experimental school of the 70s, staffed with smart, well-educated civil servant adjuncts with a real passion for their profession (OT irony
If I have read TS correctly, it is the old hat insulation you find in frame walls from the 40s, 50s, and 60s. It is so vile to work with that I have never seen an example of well-done insulation with such.
If he nails the door opening shut with modern and well-done insulation, it is likely that surface will become the best-insulated external wall in the house. Thus also the warmest. Plastic can then not reasonably pose a risk of condensation right there.
Then we can endlessly discuss whether it is appropriate for condensation to occur on building plastic or if one should let moisture diffuse through the wall and condense where the sun does not shine.
Regardless of where condensation forms, it indicates elevated humidity in indoor air. Address that first, and maybe it will be yet another example of why a house without plastic is right. Or proof of why plastic is fantastic and indispensable.
Both are so-called anecdotal evidence that proves nothing until it has been investigated what actually went wrong, or right.
Best regards, Findus
From a diffusion perspective, it is normally, with functioning ventilation, not important whether one uses vapor-tight or permeable materials.
From a convection perspective, it is of great importance that the construction is tight, for which plastic film is usually used.
If the construction is leaky and there is overpressure indoors, the risk of condensation increases significantly, most easily fixed by creating underpressure indoors.
It is often more comfortable indoors unless some dehumidification occurs.
The blanket comes from what contains moisture, laundry, showers, underfloor heating with wet clothes, people, animals, cooking.....
Diffusion is a slow process, with tight or permeable layers, negligible diffusion occurs (not negligible with porous materials)
Convection is the transfer of moisture with air currents.
If warm moist air leaks into a cold structure, condensation can form.
Explaining the whole process, which factors influence it, and why humidity strives to even out can take time.
Findus had a good schooling, right track, but still no "good" understandable explanation.
I will think further, maybe we should leave ts to their fate, major mistakes should not happen anyway.
P-A
So far, I agree with you. But I didn't see any trace of anything that explains why I am wrong.
Personally, I do everything to avoid plastic in the house. It is a short-lived, brittle synthetic material that I, on principle, don't want around me. But, having said that, a completely moisture-proof vapor barrier in the form of construction plastic is never wrong in a year-round heated house. However, it's not always necessary. However, it's essential to know what you're doing if you're not using construction plastic as a moisture barrier.
For TS, proceed as outlined, with construction plastic as the inner moisture barrier. Nothing can go wrong with that.
I wouldn't complicate it with an inner installation layer, as it's only a doorway, and there's no installation layer in the rest of the building/walls around.
I have personally closed off a doorway in our old skånelänga in this way. (Outer paneling, asfaboard, 20 cm glass wool, construction plastic, gypsum, inner paneling. Probably the best-insulated part of the whole house. After about 15 years, still no problems have visibly appeared on the inside or outside.)
For TS, proceed as outlined, with construction plastic as the inner moisture barrier. Nothing can go wrong with that.
I wouldn't complicate it with an inner installation layer, as it's only a doorway, and there's no installation layer in the rest of the building/walls around.
I have personally closed off a doorway in our old skånelänga in this way. (Outer paneling, asfaboard, 20 cm glass wool, construction plastic, gypsum, inner paneling. Probably the best-insulated part of the whole house. After about 15 years, still no problems have visibly appeared on the inside or outside.)
It is precisely the concept of "completely airtight" that is crucial for me. If it is truly completely airtight, the plastic does a good job in most conditions. However, there can be higher vapor pressure from outside than from inside sometimes, and then I would rather do without it even if it is airtight.
But in old houses where smaller and larger interventions are made (and the new ones will also become old), I think it is hopeless to guarantee the tightness over time that is needed. I have seen several cases where, for example, a ceiling hook has punctured the barrier, and when the inner ceiling is taken down, there is a puddle of water on top of the plastic. New houses have better conditions with installation layers so that the vapor barrier is protected, so a little better there.
Of course, even diffusion-open constructions should have a well-functioning ventilation system; it's not that all moisture should suddenly be ventilated through walls and roofs just because there is no plastic.
My opinion is that the advent of plastic is only due to the invention of a cheap insulating material (mineral wool) that doesn't work so well if some moisture is supposed to be transported through the wall, so then a protection against that was needed.
But in old houses where smaller and larger interventions are made (and the new ones will also become old), I think it is hopeless to guarantee the tightness over time that is needed. I have seen several cases where, for example, a ceiling hook has punctured the barrier, and when the inner ceiling is taken down, there is a puddle of water on top of the plastic. New houses have better conditions with installation layers so that the vapor barrier is protected, so a little better there.
Of course, even diffusion-open constructions should have a well-functioning ventilation system; it's not that all moisture should suddenly be ventilated through walls and roofs just because there is no plastic.
My opinion is that the advent of plastic is only due to the invention of a cheap insulating material (mineral wool) that doesn't work so well if some moisture is supposed to be transported through the wall, so then a protection against that was needed.
A diffusion-open barrier is just as open in both directions. And since there's almost always higher vapor pressure inside, it will let much more moisture into the wall than it lets out.
Sure, you can have problems if you have overpressure in the house and get holes in the barrier. But it's the same case for a diffusion-open but convection-tight membrane. Possibly a little more can dry out inward because the moisture content in the wall becomes so high.
Sure, you can have problems if you have overpressure in the house and get holes in the barrier. But it's the same case for a diffusion-open but convection-tight membrane. Possibly a little more can dry out inward because the moisture content in the wall becomes so high.
The door I have now rebuilt was in an extension that was somewhat different in construction technique compared to the rest of the house. There was plastic foil behind the plaster next to the frame, so now, of course, there will be plastic foil.
But thanks for all the answers!
But thanks for all the answers!
As previously mentioned, build like the original!
The insulation board with the "silvery" surface was a product available in the 60s, the aluminum foil was far superior to the plastic we have today as a vapor barrier but was worse in terms of handling, very easy to bump into and tear, which is why the product was abandoned when diff-tight plastic foil could be manufactured.
Just apply plastic and tape it to the aluminum foil to get diffusion-tight from the inside.
Since the temperature is the same on both sides of the foil, there can never be moisture. The only time in theory it can get moist is if you have air conditioning = much colder inside than outside and live in a humid climate like Florida, then you should have the vapor barrier closest to the outer panel. But here in the Nordics, we have warmer inside than outside.
In a Mediterranean climate, there is no vapor barrier since it's fifty-fifty which side is the coldest during the day.
Moisture always moves toward a colder environment and is deposited as water when it reaches the dew point.
The insulation board with the "silvery" surface was a product available in the 60s, the aluminum foil was far superior to the plastic we have today as a vapor barrier but was worse in terms of handling, very easy to bump into and tear, which is why the product was abandoned when diff-tight plastic foil could be manufactured.
Just apply plastic and tape it to the aluminum foil to get diffusion-tight from the inside.
Since the temperature is the same on both sides of the foil, there can never be moisture. The only time in theory it can get moist is if you have air conditioning = much colder inside than outside and live in a humid climate like Florida, then you should have the vapor barrier closest to the outer panel. But here in the Nordics, we have warmer inside than outside.
In a Mediterranean climate, there is no vapor barrier since it's fifty-fifty which side is the coldest during the day.
Moisture always moves toward a colder environment and is deposited as water when it reaches the dew point.
To get some perspective in this contentious debate:
It was about closing a doorway.
As you know, most (quality) doors have an aluminum sheet inside one or both surface layers.
Why would it be catastrophic to replace the door's aluminum sheet with a plastic film?
It was about closing a doorway.
As you know, most (quality) doors have an aluminum sheet inside one or both surface layers.
Why would it be catastrophic to replace the door's aluminum sheet with a plastic film?
No one in the thread seems to have written WHY there is plastic in modern houses. It is because there is much thicker insulation than before, which means that the condensation point is moved further into the wall. The moist air that always leaks into the wall from the inside to some extent (regardless of ventilation) therefore risks condensing deep inside the wall and causing moisture problems in the long term. In older houses with thin insulation, the wall has a higher temperature all the way to the facade, which reduces the risk of condensation. And since it is thin, it can dry out properly during the summer months.
Yes, or in combination with choosing insulation materials that cannot handle moisture very well. Even with modern insulation capabilities, you can build diffusion-open in combination with hygroscopic materials.F f91jsw said: