Christian McArdle wrote:

I am debating weather to use the Kingspan 8'x 4' sheets or
the Rockwoll roll 100 x 400 to insulate a suspended timber ground
floor.


Kingspan is vastly better on U-Values per unit thickness. U-Values are very
important and if I were you, I'd make the effort to understand what they
mean. However, it is cheaper to get the same U-Value through rockwool.
Unfortunately, this will be acquired by using a thickness many times that of
the Kingspan.


No. approximately twice, not many times.

he installation details will determine if this is a problem.
For installing in loft conversions where thinness is the key, Kingspan (or
Celotex) rules. If you have loads of space to work in, and there are no damp
concerns, rockwool may be more cost effective.

Christian.