The roof/ceiling of a typical building accounts for 30% of heating loss in the winter and solar gain in the hot summer. Many homes have duct work in the attic space which greatly diminishes their efficiency through air leakage and conduction to the unconditioned space.
By adding sprayfoam insulation in the attic under the roof line, you create a conditioned space in the attic. This spray foam insulated attic stays within +/- 5° of the 2nd floor temperature all year round causing less load on the HVAC system and lowering utility bills overall.
Spray Foam insulation at the roof line in the Chicago-land market also helps to prevent Ice Damming. It keeps solar radiation to a minimum, and help lower noise transmission from outside noise pollutants, i.e. planes, trains, and automobiles.