I have just had my loft timbers/joists treated for woodworm, and getting
the house rewired soon. After that is all done, I am going to put
insulation down. However I have some questions about it.

Is there a noticable difference in loft insulation (rockwool rolls) in
insulating greater than a 4" depth? The reason I ask is that my joists
are 4" in height, and anything greater will mean a bit more planning to
ensure that I can still walk and see the joists up there.

Also, has anyone noticed a difference between rockwool and other types,
such as crown wool? I have checked the u-values and such, and rockwool is
a better insulator, but it is also going to cost me about 20% more than
crown insulation. (b&q special offer).

I really like the idea of using natural insulation such as sheep wool :
(http://www.greenbuildingstore.co.uk/ins-thermperf.php) but the price is
unbelievable.

Any comments/help/advice would be greatly received.

Thanks.