Cold hallway and downstairs loo

[Maggie1]

My hallway and downstairs toilet are very cold. Although we have central heating and double glazing once the heating goes off they get cold really quickly. The thermostat is in the living room so it gets to temp quite quickly and the heating goes off.
Two of the walls are external and are single skin so cannot have cavity wall insulation. I have grandchildren so polystyrene insulation would prob get trashed. Any suggestions on how I can make this area warmer? I have a disabled pensioner in the house who needs to use the downstairs loo so I need to be able to keep it warm.
Thanks

 

[AronSearle]

insulation backed plasterboard is pretty much it, unles you are going to externally insulate and rendar.

In terms of robustness, there won't be much between rigid foam back plasterboard, or polystyrene insulation faced with plasterboard, in terms of insulation, the rigid foam is better.

 

[Blagard]

What AronSearle is saying is that most of the rigid foam backed plasterboards are more efficient than polystyrene backed.

If you could put up with the mess, hacking off the old plaster and fitting plasterboards with the thickest insulation that will fit will give the biggest improvement. The kingspan product below is better (for thermal insulation) than the gyproc product given that you compare two of the same thickness

Kingspan Kooltherm-K17-Insulated-Plasterboard

Gyproc thermaline-plus