Insulation on external wall

There are a few options for this: You can stick insulated plaster-board to the existing plaster-board wall if the original wall is strong enough. This can be fitted by screwing into existing joists or sticking onto the surface using an appropriate board adhesive. You could also remove the old plaster-board wall and replace with insulated plaster-board. The other thing you could do is remove the existing plaster-board, then fix some timbers onto the single skin wall to make a cavity, then insulate the cavity and fix standard plaster-board onto the new timber joists. 👍

You can build on top of existing plasterboard another frame using 50mm×50mm timber , and between tiber you can fix 50mm Rockwool and then one layer of Wallboard 12.5mm.

I do agree with other answer but I wouldn't stick plaster board ontop of existing board ,srewing the boards through onto whatever timber is under the original boards will secure them and no chance of pulling off the original plaster with the added weight .

Hi you can either screw insulation boards to the wall or stick them with adhesive, I would do both just to be sure that they are secure , then plaster