I'm finally having my freezing,70's breezeblock, batten and tongue & groove boarded bathroom tiled.(think bad Swedish sauna) The tiler has suggested I remove the tongue and groove and use insulated plasterboard. The block walls are double block thickness with a cavity between the blocks. Wooden battens have then been nailed to the block walls to allow the tongue and groove fixing. The cottage is cold, in a very damp and gloomy valley, so I'm eager to insulate as much as possible. Could anyone advise whether I should remove the battens and stick thicker insulated plasterboard directly to the block wall, leave the battens but insulate between them with rockwool slabs then use thinner insulated plasterboard over the top, or leave an air gap behind the plasterboard so it is fixed to the battens a couple of inches off the wall. I'd hate to create a perfect condensation trap and end up with water running down the walls into the kitchen below.
If anyone has any advice I'd be really grateful.
thank you.