Insulated tile backerboard rather than plasterboard

[Vaultedceilingguy]

I'm renovating my bathroom and have put 40mm insulated tile backerboard onto the two exterior walls (one has no cavity, the other does but it's tiny). I've also lifted the ceiling up considerably by vaulting it, so that it is well above the height of the loft space.

I have to plaster the brickwork exposed by lifting the ceiling up. Since this brickwork is "above" the insulation in my neighbour's house, it's pretty much an exterior wall and will tend to be cold.

I was wondering, rather than adding plasterboard and skimming, if I could use a narrow tile backerboard instead, and skim over that? Perhaps 12mm or so thickness. It'd only be a small insulating effect but it all helps.

 

[JP_]

I would put as much insulation in a bathroom ceiling as possible - high ceiling without insulation in a bathroom will mean constant bleaching of mould ...