Air gap in diffusion-open solution

[Dcaprio]

Hello!
I am in the process of building an insulated small garden house to use as a guest cottage. I understand that you can avoid the air gap behind the panel if you stick to diffusion-open materials. Does this also work for the roof, which will be open to the ridge?

The wall construction will look like this:
Panel with traditional paint
Wind barrier
Wood fiber insulation
Vapor barrier
Wood panel

Would it work with a similar construction in the roof with:
Metal roofing
Roofing felt
Roof decking
Wood fiber insulation
Vapor barrier
Wood panel

Best regards, Dcaprio

 

[nybyggarn3]

Hello!
I am in the process of building an insulated garden shed to use as a guest cottage. I understand that you can avoid the air gap behind the panel if you stay diffusion-open. Does it also work in the roof, which will be open to the ridge?

The wall construction will look like this:
Panel paint
Wind barrier
Wood fiber insulation
Vapor brake
Wood panel

Would it work with a similar construction in the roof with:
Roofing sheet
Underlay paper
Raw plywood
Wood fiber insulation
Vapor brake
Wood panel

Regards, Dcaprio

Behind the panel there should be air. In the roof, it can be built without it. It is even an advantage according to many. Then you have to replace the underlay paper with something diffusion-open.

 

[Dcaprio]

What is the benefit of the air gap when it is diffusion-open?

 

[witten]

I have understood that it is possible to avoid the air gap behind the panel if you keep it diffusion open.

Why would that be the case? Without a vapor barrier, more moisture enters the wall, giving even more reason to ventilate it away.

Additionally, driving rain becomes yet another source of moisture in the wall since there isn't a separating air gap.

 

[nybyggarn3]

What is the benefit of the air gap when it is diffusion open?

Ensures that the panel can dry optimally. Additionally, a wooden facade is never completely sealed, which means that water needs to be able to run on the backside without coming into contact with the wind barrier.

 

[Dcaprio]

Isn't that the summer thought with it being diffusion-open, that it can dry without the moisture being trapped

 

[nybyggarn3]

Isn't that the summer idea with it being diffusion-open, that it can dry without the moisture being trapped

You always build a wall diffusion-open on the outside, which is not the case for roofs. In the roof, you can skip the air gap under certain conditions. In a wall, it's not a good idea because the facade is not completely sealed.

 

[Daniel 109]

No, you must have an air gap in a roof. But if you have a moisture-open membrane under the tiles, the gap between the membrane and tiles is sufficient. However, the moisture must somehow be able to escape. I see no advantage to having a vapor barrier inside.

 

[guggen]

You don't need an air gap in the wall if you use a diffusion-open system, but then you must always ensure that the panel is painted with a non-sealing paint, usually linseed oil or distemper paint, as is the case with most old houses and often with some new factory-built vacation homes. But this is based on having reasonable insulation (maybe max 145) and nothing gets worse from having an air gap. In the roof, you can skip it if you have a diffusion-open outer membrane and a brake on the inside, which is often done today for economic reasons. But nothing gets worse here either by having an air gap even in the roof.

 

[nybyggarn3]

You don't need an air gap in the wall if you use a diffusion-open approach, but you must always ensure that the panel is painted with a non-sealing paint, typically linseed oil or Falu red paint, as is common in most old houses and also often in some new factory-type cottages. However, this is based on having reasonable insulation (perhaps max 145), and nothing worsens by having an air gap.
In the roof, you can skip it if you have a diffusion-open outer membrane and a barrier on the inside, that's how it's often built today for economic reasons. But nothing is worse here by having an air gap in the roof as well.

Regarding the air gap in the roof, there are different opinions on whether it's better to build with or without an air gap. I built my house without one, and it had nothing to do with economics.

 

[Dcaprio]

You don't need an air gap in the wall if you're using diffusion-open materials, but you must always ensure that the panel is painted with a non-sealing paint, i.e., usually linseed oil or distemper paint. This is how it is with most old houses and often with some new prefab-type holiday homes. However, it is based on having reasonable insulation (maybe max 145), and nothing is made worse by having an air gap.
In roofs, you can skip it if you have a diffusion-open outer membrane and a brake on the inside, as is often done today for economic reasons. But again, nothing gets worse if you have an air gap even in the roof.

Yes, that's what I've read too. The main house on the property is built that way and hasn't had any problems since the 60s.

 

[nybyggarn3]

Yes, that's what I've read as well. The dwelling on the plot is built that way and there haven't been any problems since the 60s

What would be the purpose of building without an air gap in the wall? Save space or some money?

 

[Dcaprio]

Surface, money, and time. But then I know if the air gap in the ceiling should find an open cloth

 

[witten]

Isn't that the idea of it being diffusion-open, that it can dry without the moisture being trapped

You keep using the word diffusion-open, but what do you really mean? I assumed you meant without a vapor barrier, but externally all walls of this type are diffusion-open. With or without an air gap. The drying inward to the room is minimal so it's not something to focus on.

Otherwise, I still refer to my first answer.

 

[Daniel 109]

He believes that the facade does not have a dense color. I would argue that despite this, there is a fairly high moisture load from the outside without an air gap.