wrote in message
ups.com...
Looking to board my attic for storage; it has some scrappy Rockwool
and joists are 4"x2". I was wondering whether to plant 2"x2" timbers
on joists to allow for greater depth of Rockwool, or maybe the
chipboard would provide enough extra insulation? Another thought -
better grade insulation material in place of Rockwool but in the same
4" space? Any ideas welcomed.

Insulation value of chipboard is negligible. Best put high performing foam
insulation between the existing rafters. Install 4"x2" joists over the
existing at 90 degrees to the existing joists, have a 6" screw through to
secure the joists, and then put cheaper rockwool between these, then
chipboard over. Check if the existing ceiling can hold the weight.

Also seal all holes in the ceiling with silicon to prevent draughts, where
cable and pipes run through. Have a sealed and insulated loft hatch. Your
fuel bills will then drop.