Your current standard board has let internal vapour through which may have condensed on the cold external wall.
Using the foil backed board would prevent this. In which case there is no need for membrane.
Kingspan K18 (or similar) fixed to timber battens on the wall would be a good option here, the thickest you can get, which I believe is 62mm (50mm insulation + 12.5mm plasterboard all in one) The insulation itself already has a foil back on both sides.
Using the foil backed board would prevent this. In which case there is no need for membrane.
Kingspan K18 (or similar) fixed to timber battens on the wall would be a good option here, the thickest you can get, which I believe is 62mm (50mm insulation + 12.5mm plasterboard all in one) The insulation itself already has a foil back on both sides.