Panel directly on tretex?

[Denniis]

Ok. And this would then be something that becomes a major problem in certain houses? I guess almost every house in Sweden experiences this in the summer when the sun is shining strongly.
Try going up to your attic yourself.
And put your hand in the insulation.
If it were to be moist (allow me to doubt), what prevents the moisture from moving upwards at night?

My attic is still warmer at night than the living area during warm periods in the summer, but maybe that doesn't make much of a difference in this context.
I believe that moisture can move upwards, absolutely. But if it's not free to move upwards, I at least want to avoid trapping any potential condensation.
Parts of my attic were furnished with plastic carpets and fitted carpets since it was used as a bedroom a long time ago by previous owners. I doubt that they could breathe upwards there.

I agree with you on many things, but I still think a vapor barrier makes sense when you don't have full control over the entire house and its construction 🙂

 

[karlmb]

Parts of my attic were furnished with linoleum and carpet as it was used as a bedroom a long time ago by previous owners. I doubt they could breathe upwards there.

Of course, it's foolish to lay linoleum on the cold side (which it becomes if you live below and don't heat above). Using dense materials in the wrong place is something nobody would argue against. On the other hand, not having a full understanding is no reason to choose open materials. It's not that difficult really. Moisture migrates towards the cold side in an insulated wall/ceiling. Moisture that has migrated all the way through and comes out into a colder space can condense and turn into water on the coldest parts of that space. So, you want to reduce moisture migration, not allow it with some kind of "breath" argument. A house should be ventilated, but it's not a lung. Where moisture exists, it should be ventilated out in a safe way. If unsure whether, for example, the ventilation is sufficient in a cold attic, it's never wrong to reduce moisture migration up to the attic by sealing clean air leaks and reducing diffusing moisture that goes through the building materials. Many believe that the only way is to ventilate more or even dry the air at great energy costs. But if no moisture exists, there's nothing that needs to be ventilated or dried. However, continuing to add moisture to the attic in an old house by, for instance, starting to live in it in a modern way with high temperatures and bathrooms, and installing a vapor retarder in the ceiling, will cause more problems than putting plastic in the same area. A tip today is to install cheap temp and hygrometer units on Zigbee which last a year on a battery, costing about 100 SEK each. Through a phone app, you can easily monitor and see how humidity and temp change over the seasons and determine if you have a problem or not.