Vent or Not to vent
Hey yal!
I looked in to buying into foam spraying buzz. I like the benifits of the product! However when I seen them spraying it to the bottom of the roof sheeting, venting came to mind. I opinion is, a well vented roof deck is going to help the life of the shingles. I use ridge and gable vents combined with full soffit vents, good air flow. I put 1x2 furring strips on edge, stapled to the truss or rafter. This gives me my airway space 2"nom., then I use 1.5 or 2in. ridgid foam cut snug, can always foam gaps though. I'll run this from the top plate up at least 4ft. for a flat ceiling and all the way to the ridge for vaulted ceilings. But with this foam system one could use those cheesy cardboard or foam airways or propervents and that could maintain your air gap! Then I feel you may have some thing. It would be worth the time and cost, heating or cooling you deal with the same issues. Unless you live in a stable climate such as Hawaii! Note when I cut open a ridge after shingling its like a blast furance, hot air rises. Helping to keep that deck and shingles from burning up and curling up!