On 06/03/14 10:19, Mathew Newton wrote:

I am still getting to grips with calcuating U-values so I might give
that alternative a thought. I'd always assumed PIR boards were
generally always better performers than mineral wool etc for a given
thickness though?


You are correct - PIR foam (aka celotex etc) is about twice as effective
for a given thickness compared to most wool type products.