Insulating the underside of the roof has many advantages over insulating the ceiling of the living space below the attic.Creates a comfortable interior in the attic (not the suffocating heat in the summer, or escaping heat in the winter).Lets the HVAC unit and the Ductwork, work in a more moderate environment, thereby not overworking to overcome the extreme heat of a uninsulated attic. Less AC Unit CyclingLower the Temperature in your home more efficiently