Insulating external stone wall

[koomber]

I'm looking to insulate an external wall whixh previously had plasterboard on battens. Due to space restrictions in the room and cost, what I'm planning will be 50mm omnifit mineral wool insulation between the battens and 20mm kingspan over the top of the battens.

The room will be used as a bathroom.

One thing I've been told is that the mineral wool will act as a sponge for moisture if it is in contact with the external wall. With the state of the wall the wool will come I to contact with the external wall in few places.

I've seen installation guides where the mineral wool slabs are just wedged I between the battens in contact with the wall.

I'm not so concerned about moisture from the bathroom as the kingspan will act as a vapour membrane so it should only be an issue of the wall breathing.

Will I be okay to wodge the mineral wool in there or will it create a damp problem in future. I've had the wall exposed for some time and have noticed no water getting in from outside.

 

[endecotp]

I’m in the middle of a project to insulate the 3-foot-thick external stone walls of my flat. It’s a listed building, so I had to get proper advice.
I’m required to have a minimum 25mm gap between the stone and the insulation, and because of unevenness I’m aiming for 50mm. I’ve fixed netting to the studs to help prevent the insulation from slumping back against the wall.
It soinds like you don’t have enough space to do that. You might be better off using kingspan between the studs. There is no danger of it slumping, and even so it doesn’t much matter if it touches the stone because it has an impermeable foil surface. That also has the benefit of providing more insulation.

 

[tomfe]

Us 25mm battens and 50mm pir will give you the same uvalue, if not better, and you keep the 25mm gap.

 

[endecotp]

Good plan tomfe.