OSB on "cold" side of roof ?

[bodger_badger]

Hi,

I have a loft room with attic trusses, with fibre glass insulation in both the vertical and sloped bits of the roof.

I'd quite like to add some OSB to the cold side of the vertical supports, so it'll be plasterboard, insulation, OSB - but I wasn't sure if the fibre glass insulation needs to breath?

Thanks

 

[freddiemercurystwin]

That would be fine. We assume the the sloping rafters have an adequate ventilated void. Typically you would only do one or the other, either insulate the dwarf walls or insulation the sloping section.