Vapor barrier or not?

[Självbyggare2019]

An old thread but filling in to prevent others from getting confused by reading the thread.

The whole idea of a vapor barrier is to prevent the migration of moist air between different temperature zones. Without the barrier, moist air from inside or outside can travel and deposit water inside the wall where it meets a cooler surface. That is to say, the barrier removes the problem regardless of the outside/inside temperatures.

Since it is difficult to be sure that the climate screen (vapor barrier) is completely sealed (which it practically never is 100%), it is wise to install a mechanical exhaust fan in a house where the interior temperature is 20 degrees and humid to ensure that any migration occurs inward and not outward. In a cold garage, it might not matter, but if it's warm, install a fan.

Air migration can occur where you least expect it. For example, the sheltered side of a house that is in a windy area is particularly vulnerable as a vacuum can be created there, which can act as a force pulling indoor air out through the wall.

When building, always follow the current industry standards regardless of what people say here. This way, you avoid problems with insurance companies in case of future damages...

https://www.isover.se/news/ska-fritidshus-isoleras-och-plastas

 

[nordstroem.mikael]

It's kind of funny, this.

In your link to isover (manufacturers are usually good sources)

Is it okay to use traditional plastic foil in the constructions of summer cottages?

A traditional plastic foil cannot capture condensation, resulting in moisture - summer condensation - dripping off and being absorbed by the construction wood, such as in the sills in the exterior walls. It is an unnecessary strain.

 

[BJER]

After following many threads about moisture and mold in small houses, one gets the feeling that no matter what you do, it's like a lottery with everything, so what should you do???

 

[Flanders.Be]

An old thread but filling in so others won't be confused by reading the thread.

The whole idea of a vapor barrier is to prevent the migration of moist air between different temperature zones. Without the barrier, moist air from inside or outside can migrate and precipitate water inside the wall where it encounters a cooler surface. In other words, if the barrier is present, the problem disappears regardless of the temperatures outside/inside.

Since it's hard to be sure that the climate screen (vapor barrier) is completely sealed (which it practically never is to 100%), it's wise to install mechanical exhaust ventilation in a house where the indoor temperature is 20 degrees and humid to ensure any migration happens inward and not outward. In a garage that is cold, it may not matter, but if it's warm, install a fan.

Air migration can occur where you least expect it. For example, the lee side of a house in a windy area is particularly vulnerable as it can create a vacuum that might act as a force pulling indoor air out through the wall.

When building, always follow the current industry standards regardless of what people say here. That way, you'll avoid problems with insurance companies in case of any future damages...

[link]

From the link "However, there is much uncertainty as to whether it is good or bad to use a vapor barrier/vapor retarder." Nothing is self-evident when it comes to moisture, and industry standards are sometimes poor construction techniques, such as air gaps in the roof.
I don't know what's "right" (read: best), but DIYers who give clear-cut answers don't know what they're talking about.

An old thread but filling in so others won't be confused by reading the thread.

The whole idea of a vapor barrier is to prevent the migration of moist air between different temperature zones. Without the barrier, moist air from inside or outside can migrate and precipitate water inside the wall where it encounters a cooler surface. In other words, if the barrier is present, the problem disappears regardless of the temperatures outside/inside.

Since it's hard to be sure that the climate screen (vapor barrier) is completely sealed (which it practically never is to 100%), it's wise to install mechanical exhaust ventilation in a house where the indoor temperature is 20 degrees and humid to ensure any migration happens inward and not outward. In a garage that is cold, it may not matter, but if it's warm, install a fan.

Air migration can occur where you least expect it. For example, the lee side of a house in a windy area is particularly vulnerable as it can create a vacuum that might act as a force pulling indoor air out through the wall.

When building, always follow the current industry standards regardless of what people say here. That way, you'll avoid problems with insurance companies in case of any future damages...

[link]

 

[Daniel 109]

When would an air gap in the roof be bad?

 

[Flanders.Be]

When would an air gap in the roof be bad?

Almost always according to experts at LTH, roofs are almost impossible to build and an air gap is not sufficient unless all parameters are perfect, aka if it rains during construction, the air gap is not enough! But it's off-topic so sorry for bringing it up.