I am renovating a very small cloakroom which has two external walls of solid 9 inch brickwork, plastered.
The lower half of the walls will be traditional tongue and groove panelling. However I would also like to insulate the upper half, but without making the room too small.
I would like to fix some thin but effective sheet insulation directly to the existing plaster, which is sound, and cover it with plasterboard. Ideally, the insulation would be 20-25mm thick.
Any suggestions as to what to use? Also how best to fix it, and the plasterboard on top, and how best to join the plasterboard on the wall to that in the window reveal to give a neat corner joint.