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5 replies
3k views
5 replies
What is air barrier paper good for???
I am in the process of replacing the old peat with linen wool insulation in my pitched roof. There has never been an air gap, and I have no possibility to add one now. The idea is that the linen wool insulation should be able to breathe in the same way that the peat has worked for the past 90 years (i.e., without issues).
From the outside in, it now looks like this:
Råspont
Linen wool
Air barrier paper
Gypsum or interior ceiling panel
My questions:
1. I thought I understood the function of the air barrier paper, but what does it really do? Does it stop air? To what benefit? The fact that it can let through vapor means that the linen wool can dry both outward and inward, which is good, but doesn't that also mean that all moisture from inside the house ends up directly in the linen wool??:S
2. I plan to put gypsum in the interior ceiling, could this impair the house's ability to breathe?
3. In some places where the spans are large, I plan to put an OSB board followed by gypsum for the interior ceiling. It would help if I could place the air barrier paper between the OSB and the gypsum. Could this be okay?
4. When I tore down the old interior wall, it consisted of two layers of råspont with a tensioned paper in between. Is tensioned paper the same as air barrier paper?
From the outside in, it now looks like this:
Råspont
Linen wool
Air barrier paper
Gypsum or interior ceiling panel
My questions:
1. I thought I understood the function of the air barrier paper, but what does it really do? Does it stop air? To what benefit? The fact that it can let through vapor means that the linen wool can dry both outward and inward, which is good, but doesn't that also mean that all moisture from inside the house ends up directly in the linen wool??:S
2. I plan to put gypsum in the interior ceiling, could this impair the house's ability to breathe?
3. In some places where the spans are large, I plan to put an OSB board followed by gypsum for the interior ceiling. It would help if I could place the air barrier paper between the OSB and the gypsum. Could this be okay?
4. When I tore down the old interior wall, it consisted of two layers of råspont with a tensioned paper in between. Is tensioned paper the same as air barrier paper?
where does the term "luftspärrpapp" come from then? on the outside behind the panel is one thing but inside it can't serve any function other than to hold the insulation in place? In the past, they tried using tarred paper before plastic came but it's just as tight as plastic is. Paper also allows moisture migration as mentioned.
Okay, is this understood correctly:
Diffusion = humid air moves through material because it seeks to have the same vapor content on both sides
Convection = Humid air blows through material.
Plastic vapor barrier: Prevents both diffusion and convection.
Air barrier paper: Only prevents convection.
In my case, the moisture normally migrates from the room through the air barrier paper into the insulation since I mostly have a higher vapor content in the room. However, the vapor content can never be higher in the linen insulation than in the room because then the moisture would start to go in the opposite direction back into the room.
How does this reasoning sound? Have I understood it correctly?
Diffusion = humid air moves through material because it seeks to have the same vapor content on both sides
Convection = Humid air blows through material.
Plastic vapor barrier: Prevents both diffusion and convection.
Air barrier paper: Only prevents convection.
In my case, the moisture normally migrates from the room through the air barrier paper into the insulation since I mostly have a higher vapor content in the room. However, the vapor content can never be higher in the linen insulation than in the room because then the moisture would start to go in the opposite direction back into the room.
How does this reasoning sound? Have I understood it correctly?
Yes, that sounds quite right. It depends partly on the heat outside and inside as well.
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