Made a fool of myself with vapor barrier?

[klaskarlsson]

Hi! I am in the middle of an expansion of 50 sqm on my existing house (former summer house) built in 1989.
The existing house has 120mm glass wool insulation and plastic on the inside.
The extension has 170mm rock wool in the walls (+45mm rock wool on the installation batten) and the plan is to blow cellulose into the ceiling and floor.
But I am afraid I may have messed up, I initially planned to use plastic in walls and ceiling, but the carpenter convinced me that a vapor barrier is a better solution since it breathes. I have then mounted a Halotex D20 with an sd value of 2. (The outside has a wind barrier at 0.035 sd so the inside is 5 times tighter)
Is it a bad construction? Should I address this or just sit tight? We have already started closing the walls with plywood so it is not a "quickfix" to arrange. We use the house as a permanent residence and it will always be heated.

That will probably work excellently.
It would probably have worked with a vapor barrier too since you are building new and taping properly, but I see no problem with a vapor brake there ...

 

[henryry]

There is stone wool in the walls, and we will blow cellulose into the ceiling and floor. I am well aware of this, which is why I am unsure about my choice as this is not a vapor barrier but a brake.

I have exactly like this - mataki d20 (actually supposed to be a different one in the ceiling). Built on the house in 2020 and now five years later I got the opportunity to inspect due to another project. I felt a bit worried that there might be some problem with the "wrong membrane" but it was completely dry and still smelled new.

 

[Tomture61]

In houses with heat recovery ventilation, there is usually a certain negative pressure in the house. In such cases, using a vapor barrier is necessary.

In houses with natural ventilation, a vapor retarder works just fine, cellulose insulation is preferable then.

If you use mineral wool in the building envelope + natural ventilation, both types of foil work.