Attic areas above the ceiling of the top floor of the house were electrical, phone lines, Cable TV and some times gas lines as well as chimneys and vents. Attics are an odd place to insulate. Do you want the homeowner to have access or not to the attic this question must be answered first. If you don’t need access then blowing or spraying in insulation on top of the ceiling is fine.
But if you need access batting in the insulation or spraying in insulation in between the rafters against the roof sheathing works good.
Keep in mind that heat rises and fiberglass, and mineral wool insulation acts like a furnace filter air past through it.
The more fiberglass, or mineral wool you use slows the air transfer making it harder for air to move through it.
With Icynene insulation the first inch of insulation does the most work stopping any air from moving into the insulation, IE no heat transfer in the air movement through the insulation.Touch on picture to enlarge
Keeping the humidity on the inside of the building were we want it. So if you have tight spaces to insulate and regular insulation will not give enough volume of insulation 12-16″ thick for a good R-value.
Than please use Icynene insulation even if 6″ is all you can get in there, it still will save you 30-50% on your heating bills.