I had liked the idea of cold roofs for a long time also I like the idea of having more roof overhang. So when I added a bedroom and livingroom to our home I had to redo the existing roof. It would have been a great deal of trouble to extend the roof on the North side so what I came up with there, after removing all the three tab shingles and felt underneath, was to cut off the existing overhang even with the stud wall after which I screwed seven runs of 1"X4" firring evenly spaced horizontally across the roof sheath and where each rafter was I screwed 2"X4"s vertically that had a two foot overhang. On top of these 2X4s I nailed 1/2" plywood sheathing. For the South side roof I had to built a new rafter system for because of the room additions, it is not a cold roof but it is isolated from the existing construction by me leaving the old sheathing in place. The attic above the new construction is insulated with 12 inch fiberglass. The pic of the West side shows the original South wall, Black arrow and the original roof line in White. Roof is vented clear across the top under the metal peak cap. The second pic shows the double vents for the cold roof. Last summer when we had 100 degree temps it was 80 inside and this winter in the coldest of days, teens and twenties, our wood stove fully dampened was at times too warm and we often had to opened a window.