You could "beef up" the insulation by installing foilboard in the following manner:
Plaster board 13 mm
90 mm timber frame with Bradford hp r2.5 batts
Enviroseal proctor wrap
25mm metal battens
Foilboard
25mm battens
Loxo panels 50 mm thick.
If you were to go the above route, get a structural engineer to provide advice on fixings and battens. If you've allowed for the Loxo panels to weightbear on the the slab, space to fit the above in may be an issue. You will also need to address the venting and draining of both cavities as the Foilboard will now become your drainage plane. Also, you'll need to re-assess about how you detail weathertightness around window and door openings with the wider wall. There are alternatives to Foilboard which may save you some space (but my understanding is the two cavities will need to stay, regardless).
I wouldn't direct fix the Foilboard (or similar products) to a timber frame (others may disagree, for sure). Water vapour does need a way out. For the walls, vapour will move through, hit the Foilboard and likely condensate on the inside if it's been cold for a while and the dew point has moved to the inside (generally speaking, insulation only slows the movement of heat / cold). In the past, and even now, condensation has been a hit and miss affair. If the house was 'leaky' to air movement, sometimes vapour/condensation control looked after itself by the (uncontrolled) airflow... and sometimes it didn't. If your plan is to make your house airtight (or the better part of it) then you'll need to deal with water vapour movement. You can also look at options like HRV / ERV / humidity controlled aircon to assist in this. Or open windows (which may defeat what you're trying to achieve).
I think you're correct about the batts; if you're using a breather membrane, having the batts close / touching the membrane is ok.
Posted Friday 28 Apr 2017 @ 1:39:32 am from IP
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