A 2 X 10 rafter with a high density batt insulation leaves a one inch air space for ventilation while still providing an R-30 insulation value. A radiant barrier can also be worked into this design. The foil side must face the air space. For a gable roof on a house 28' X 52', calculate the amount of vent space needed for natural ventilation. Indicate square feet of soffit vent spaces and square feet of ridge vent.
Cool air rises.
Bring air in as low as possible and vent it out as high as possible. One drawback of attics fans is that it has a tendency to pull conditioned air from the house into the attic. The ridge vent is the best place to bring in air form the outside. The soffit vent assures a good flow of outgoing hot air form the attic. Two ways of reflecting the sun's energy is roof color and radiant barriers.