I just purchased a 1952 2x6 raftered home with three gables. The attic has about 6" of some type of old blown in type insulation, and does not appear to have been very well ventilated - vents on gables partially blocked with aluminum siding.
In the past I have laid 2x4 sleepers over an existing roof, sheathed over them, and installed new shingles with ridge vent to improve ventilation. In this case, I'm considering a similar modification, but since this home has an attic, I'm considering tying the existing vented soffits into the new vent space created by the 2x4 sleepers, and either eliminating venting to the attic itself, or only using some type of gable vent. I want to blow-in enough additional insulation to bring the R value up to current standards (R-38 here in the Upper Peninsula of Michigan).
Is anyone familiar with this type of roof over, or foresee any problems I may encounter?