Hugo Nebula abuse@localhost wrote:
On 29 Nov 2006 04:07:48 -0800, a particular chimpanzee named
randomly hit the keyboard and produced:

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.
snip

You'll get better value from your insulation if you use the Celotex
over the rafters and the polystyrene between. There is heat lost
through the rafters and the more insulation you can cover them with
the better.

To put some numbers on this - wood has a conductivity of about three
times that of rockwool or polystyrene, and six times that of kingspan.