Hardie Backer/knauf Aquapanel + insulating board

[Comedydave]

Hi
I've googled extensively for this with no luck.

I'm redoing the bathroom, with the bath/shower against the external (215 mm solid brick) wall. At the same time, I'm redoing the other external walls in the house with 60mm PIR backed plasterboard.

I want the same thermal effect in the bathroom, but i'm loathe to use insulated plasterboard here as I've read that cement board/aqua panel/marmox is generally better than tanking. So I'd like to put 60mm PIR board with cement board on top.

So my question is: how best to secure the aquapanel/hardie on top of the insulation board?

I'll be using dot n dab with mechanical fixings for the other walls.

Some methods I've thought are:
- super long pre rawled screws through cement board and insulating board into wall. Downside: vapour layer compromised.
- batten wall with 3x2, put PIR blocks in between, screw hardie board into battens.
Downside: cutting PIR means more chance of vapour being behind; cold bridges at battens.
- batten wall, then insulating foam and hardie board screwed into it. Downside: wall is now coming 10cm into room....

Any help appreciated!

 

[chappers]

How about thinner battens to the wall with less insulation (40-50)between then overdraw with 25mm joint taped PIR to cut out cold bridging then then cement board over.
Also battening over your solid wall wont cause anywhere near the cold bridging issues associated with say a timber roof or wall construction

 

[Comedydave]

Hey Chappers, thanks for the idea. I think your suggestion could indeed work and cut down on any problems with bringing the battens to the front. Cheers!

 

[chappers]

most welcome