Dean Richard Benson wrote in
news

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.

Can't answer quantitatively, but for the same reason I put down 4inches
(HTF does one cope with a foot of insulation?)

It's made a big difference, there was already a skimpy fibregass layer
there, but it's pretty well just the 4 ins.

So I think I would stick with 4 ins ant take the losses, at least I can
still find joists, wiring, pipes, chimneys etc.

mike r