Making major repairs, a private house, ceilings 2.80 m, I want to do suspended ceilings of plasterboard, and not to lose heat by putting 50mm mineral wool. Is there a feasibility of it?
It is more reasonable to insulate the floor on the attic side
If you lower the level of the ceiling – yes, the heat will be at a different level, less cost for heating and heat storage. But are you happy with the lowered ceiling height? We're talking about a few dozen centimeters.
What is the ceiling made of? I would remove the slag and insulated with mineral wool. If the ceiling is wooden, you need to put a vapor barrier under the wool.