[vixstix]

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.

[pgkevet]

It's not my field of expertise but instinct suggest that you need to create a vapour barrier to the outer block wall...perhaps external paint or injected slicone into the outer blocks then insulate the gap between block walls (? foam injection) before any additional internal lining. Finally add ventilation to pull moist air out of the bathroom with an extractor or dehumidifier as well as heating the room to reduce condensation onto the new tiling.

[valmet10]

you would be better stripping the walls and using thickest insulation/plasterboard you can , if you leave the battens on the wall you will have cold spots because there wont be as much insulation at this  point  so may condensate more , good ventilation is  a must 

[vixstix]

Thanks for your advice valmet10 and pgkevet. I'll strip back to the blocks and fit the thickest board I can.

[cloddopper]

Hard earnt experience , gained from doing up five of my own homes :-
.

Don't for get to put a more than adequate extractor fan system linked to the room lighting on a 45 min or longer timer . Make sure it is not set up so you have a straight short circuit of air that is sucked in via the door  goes in a straight line out of the extractor .
Having the dry incoming air to the room squirling & swirling round the room is what your looking for as it collects moisture best ..

 I have two 240volt  in line extractors with 12 volt safety lights  on a 45 min timer . one is in the ceiling above th shower cubicle the other  six feet away  in the ceiling over the deep end of the bath .

 Even then if both Alison & Munchkin get the enormous bath towels sopping wet from 3/4 drying their drying their very long hair off  ,  the extractors will struggle to move the evaporating air after they put the towels on the towel rack unless we leave the light on for several hours .
  One of the biggest problems in cold place is warm humid air condensing on cold walls or having already been condensed it seeps into plaster boarding or down cracks & crevices .
 So it's worth  putting th extractor on a minute or so before you start producing the high moisture levels so the air can already be moving out of the room ..it will be far more effective in taking the moist air out once it gets this " bump start "