Vapor barrier or not in unheated space.

[självlärdtornedalning]

My grandfather built a cabin with:
75mm of glass wool in the walls + 12mm of asphalt board on the outside and windproof fabric on the inside.
The floor has 2x 70mm of glass wool and windproof fabric on both sides.
2x 75mm of glass wool in the roof + 12mm of asphalt board on the outside and windproof fabric on the inside.

It has been standing since the mid-60s with very good results, despite not being permanently heated. It smells fresh and has no mold infestation - I assume this is a good solution, as the asphalt board is equivalent to about 38mm of glass wool and the windproof fabric keeps dust and insects away from the insulation.

 

[Tomture61]

I have plastic in my unheated garage since 1981 and have no problem with it
95 mm insulation in the wall and 200 mm in the ceiling

What you can't see can't affect you.
Have you checked behind your drywall.

 

[tergo]

What you can't see can't affect you.
Have you checked behind your drywall?

Yes, I changed 3 boards 5-6 years ago and it looked good on the backside.