Will 12mm OSB be permeable enough to prevent condensation for cold-roof?

[hanvyj]

Hi,

 

I was just boarding my garage roof with OSB and a builder next door told me that I might want to be careful for condensation as I'm using insulation between my joists. Here's the construction as I've currently got it planned (at the moment I'm laying the OSB. Some insulation is left over EPS, some will be rockwool, if that matters)

 

I'd planned it with a ~68mm ventilation void above the joists, as I'll be adding counter battening under the steel roof itself, but hadn't considered if the 11mm OSB would be vapour permeable enough. Here's the general layout:

 

Does this look sensible?

 

[Mattg4321]

Surely you want a VCL directly behind the plasterboard?

[Temp]

I think it should be ok if the ventilation void is well ventilated.  That means ensuring each bay between joists/battens is ventilated both ends.

 

1 minute ago, Mattg4321 said:

Surely you want a VCL directly behind the plasterboard?

 

+1   

[hanvyj]

19 minutes ago, Mattg4321 said:

Surely you want a VCL directly behind the plasterboard?

 

I hadn't originally planned to, but I'm certainly going to put one in now yes.