Gable wall insulation

[FRAN1870]

Sorry guys but more questions

I've calculated the roof insulation for the loft conversion but just in two minds in respect how best to stud and insulate the gable ends to prevent interstitial condensation.

Celotex will need a ventilated air gap but will this mean putting an air brick in or just leaving a gap ?

Alternatively I could try rockwool with foil backed plaster board ?

Thickness isn't really an issue

 

[theprinceofdarkness]

Put your battens up, line them as tightly as possible with your foam, sealing any gaps with expanding foam, cover the lot with a VCL (cheapo, lightweight plastic sheet. Screw your plasterboard onto the battens. You get interstitial condensation, when moist air cools. With my arrangement, the inside of the outside wall should be at the outside temperature and no moist air can get to it as there is a VCL in the way.
Frank

 

[^woody^]

Celotex does not need an air gap when used as internally lined insulation

 

[FRAN1870]

Celotex does not need an air gap when used as internally lined insulation

I understood that you could also get the same effect from the outside coming in ? Meaning that moisture could get trapped between the brickwork and the celotex and rot the studs ?
Is that not the case ? - sure I read it somewhere but tbh I've read so much these last few weeks that my brain is mush !!