Insulating inside of exterior cavity wall

[Aerate]

I was thinking of boarding out the end wall and side walls of a dormer window bedroom that has cavity wall insulation with 50mm of PIR insulation, Unfortunately being quite exposed and west-facing, the insulation in the cavity walls doesn't seem to be cutting it. The walls are cool to the touch, but there is no damp or condensation visible. Is there anything to stop me fitting some 50mm insulation boards directly onto the wall and then covering them in tongue and groove MDF?

[Terminator X]

You can get insulated plasterboard now so 12.5mm p/board with 50mm of insulation etc pre glued on.

TX.

[Aerate]

Thanks Tx – I have actually used insulated plasterboard before, but I have an aversion to plastering. Plasterboard will allow a certain amount of moisture to pass to a fro through it I believe, but I guess if it has foil-backed insulation attached to it it can't be breathable QED I can use MDF panels!

[CaptainScarlet1967]

Would MDF not be weaker in the grand scheme of things and more prone to any kind of moisture damage not necessarily from the structure, swelling etc than insulated plasterboard?

I've used insulated plasterboard before (same as above: 50mm PIR bonded to 12.5mm plasterboard), and IIRC there is a foil vapour barrier hidden between the PIR and the plasterboard. It has made a huge difference where I have used it.