You are reading a single comment by @JonoMarshall and its replies.
Click here to read the full conversation.
-
The details matter, the risk of condensation/moisture build up on the inside of the exterior face is also important (if you allow moisture into the wall from the inside).
The scenario you describe suggests inappropriate rock wool use as the exterior face couldn't have been adequately vented/permeable?
Individual dew point/humidity calculations based on local climate and the different options you're considering should highlight what's best.
JonoMarshall
I'm not an engineer, but from experience I have reservations regarding plastic (or Tyvek) next to rock wool. I've seen massive blooms of fungus in rock wool that was covered with plastic. The plastic meant the humidity couldn't escape properly. Re-did the wall with the same amount of rock wool etc just without the plastic and that problem did not re-occur.
For that reason I am sceptical to the suggestion further up thread where someone wanted to add a layer of boards on top of the insulation in their attic. That insulation then becomes a sponge for all the steam rising from your shower and kitchen.
That being said, I am sure having vapour control layers can work wonderfullly, if we're talking new builds where the engineers know exactly what they are doing from the start.