Hi,

Im in the process of insulating the roof of my garage.

I am planning on using 50mm Celotex between the rafters. Due to cost,
I was planning on using 25mm polysterene from B&Q over.

Would I still need the vapour barrier plasterboard ? Or if I ditch the
polysterene could I just tape up the joints where the Celotex meets the
rafters and use standard plasterboard ?

Thanks,

Matt