Suggestion on IWI of an old 1850ca cottage

[frzac]

I am approaching the start of the refurbishment of my old 1850 listed cottage and I would like to hear your experience regarding the insulation of solid stone walls.

Mine are made of 500mm of solid Welsh stone covered with about 20mm lime plaster, entirely substituted or patched in some rooms with gypsum plaster(pink one). Everything is covered by glued paper that has been painted over the years (clearly the walls are not so breathable).

On the external, 3 sides are exposed to external weather, one is sheltered by a neighbouring building. The only exposed gable wall is covered by 20mm of cement plaster (not perfectly adherent to the wall) which should offer a degree of protection from rain. This layer will be removed in the refurbishment to expose the rubble stones.

 

Our architect suggests repointing all walls (wise) and using an insulated plasterboard with integrated VCL directly attached to the wall, with 30 mm insulation + 12.5mm plasterboard. I am not sure about this method since it could lead to potential future issues especially when we remove the external plaster on the gable end.

 

Which insulation type would you suggest for those external walls to avoid or mitigate any potential condesation/infiltration risks?

Would you suggest removing the plaster before applying any insulation?