This house is already under a large shade tree, but, in order to make it a true "ductless" home, we need more than that to be free from the need of an air conditioner. The purpose of double roof decking is to put this entire house under "another roof" with sufficient ventilation in between, kind of like placing the house inside a barn without walls.
The advantages of double decking, in addition to keeping summer heat out, also gives the roof one extra layer of protection. We put ice-and-water-shield over the entire bottom layer of roof decking. So, even if the house is totally neglected for decades, the roof damage will likely only go as far as the top layer roof decking and the bottom layer will still be intact.
1x2 are used for spacing the two roof decking at 24" on center, sitting right above the roof rafters. 2x2 would have been better, but it is harder to work with. The layout needs to be in such a way that provides strong support and sufficient ventilation.
Coming Next:
Double Wall Ventilation
Ductless Homes
Building Process
