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vapour control layer on the inside of the rock wool
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.
starfish&coffee-
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
If you're doing it properly you put the boards on stilts so there is still an air gap between the insulation and the board.
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Probably more one for the DIY thread but if you are going to line externally facing walls in single skin brick wall stuff (aka victorian / Edwardian) you need to be careful about both vapour in the property being able to get out, and vapour coming through the brick and plasterwork being able to get out. That means either breathable materials, or very clever and thorough moisture barrier stuff.
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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.
aggi
Howard
JonoMarshall
If there's no air gap then you'd need a vapour control layer on the inside of the rock wool which would ideally tape to the equivalent in the floor/wall below.
I've just done internal wall insulation for a 3-floor victorian terrace. Kind of wished I'd re-hung the joists on thermally broken wall hangers given plenty of them were rotten at the rear of the property, but hindsight is 20-20.
Ended up going down the air gap, 100mm PIR, air tight membrane plus heat recovery route... should be toasty, dew point calculator was happy too. EPC will go from E to B (eventually).