Hello!

I'm not planning to use plastic behind the panels in my small shed that will be partially/periodically heated. The usage might change in the future to a dog house/chicken coop/storage.

Yeah, the usage will probably change, but the building is insulated.

No plastic, I guess? :)
 
OXYD
Is there ångbroms fabric if you want something in between?
 
doesn't the gips brake as well? :)
 
no one who has built similar ones with varying uses?
 
OXYD
That is why manufacturers recommend steam brake fabric for cottages and garages.
 
OXYD
Yep, all too expensive. Some people here on the forum have used regular vindduk. But whether it's a fully adequate solution, I don't know. It's not as tight as ångbroms.
 
OXYD
But search here on the forum and you'll find more info about unplasticized garages. But be prepared for a lot of talking/opinions about whether or not to use plastic/vapor barriers.
 
byggmax does not have in store....
 
Mikael_L
Gypsum board itself is quite vapor-permeable. It is primarily the paint on the boards that, together with the board, can achieve roughly the same vapor resistance as a vapor retarder. It is impossible to know the total value reached with the construction, but in practice it will be something in this range.

If the vapor pressure inside the shed is greater than outside, water vapor is pushed out in/through the walls, and plastic or a vapor retarder can be beneficial. If it is cold inside the shed or there is no "production" of moisture, there will be no vapor pressure and vapor migration to manage. A person "produces" 1 liter of water per day just by being in the building, we exhale 1 kg of water vapor per day (a little over).

Thin walls are generally much less sensitive; they reach moisture equilibrium with the environment much faster and thus dry out quickly when conditions permit.
 
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Mikael_L
OXYD said:
Yep, all too expensive. Some here on the forum have used regular wind barrier. But whether it is a fully adequate solution, I don't know. It is not as tight as a vapor barrier.
In terms of diffusion, wind barrier is almost completely open. But it stops air convection.

Convection is the mechanism most capable of carrying large amounts of water vapor into the construction, so it can be a good idea to seal leaky walls and constructions with wind weave if it is the simplest way.
 
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OXYD
Good answer Mikael_l. 👍

"Bison Steam Brake works excellently together with Bison Wind Shield and also with Bison DiffRoof. This creates a condition where the inner fabric is more than 5 times as tight as the outer fabric on the wall. In the ceiling, you get a condition where the inner fabric is more than 10 times as tight as the outer fabric. This is in accordance with guidelines that advocate these specific conditions."
 
the walls are 95mm
the ceiling 145mm

maybe I'll put a wind barrier inside as well =)
 
there will be plastic under the roof insulation too, we thought.

then the roof will look like this from the inside
gypsum
sparse panel 20mm
plastic
trusses 170mm (with 145mm insulation and a top 25mm air gap = 170mm)
underlayment/walkable felt, unfortunately diffusion-tight as we saw after the roof was installed
batten 38mm
roof sheet tp20

so there will be 2 layers of diffusion-tight in the roof... with an air gap under the upper layer...
believe in this construction anyway :)
 
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