"Christian McArdle" wrote in message
et...
Is there a noticable difference in loft insulation (rockwool rolls) in
insulating greater than a 4" depth?

Yes. The law of diminishing returns says that 350mm is the best
environmentally speaking. Any more and the environmental cost of
manufacturing and transporting the insulant is higher than the energy
saved.
100mm is definitely on the low side. 200mm would be better. The difference
between 200mm and 350mm isn't that great.

Are you sure on this. It's just I heard the ODPM people who set the
building regs were talking about as much as 450mm in the next part L.

Rockwool is on 3 for the price of 2 at Wickes and so matches the B&Q prices
well.