Well, we got a step ahead of ourselves, thinking that with our vaulted ceiling we could just fill the cavity with insulation and be fine, but recently several people expressed concern that it HAD to be vented. By the way, this is in Western MT in a cold climate.
So, we painstakingly drilled 1 1/2 inch holes all along the tops of the I-Joists as well as the rim rafter, into the soffet and put in R-38 C so we had a couple inches for air travel up there. The metal roof is on and has NO ridge vent, so we are putting in several "turtle" vents near the ridge, thus drilling the tops of the rafters so air could circulate between them since we didn't wantt to put a turtle vent over every single rafter cavity. 1st question: should we put a fan assembly in the turtles to create a better pressure gradient and keep the air moving? Yes, the soffits will be continuously vented.
2nd question: Do we need to put a polyethylene vapor barrier on the ceiling? The ceiling is going to be T&G pine. THe only concern I have about this is from someone telling me that vapor will go through the wood (or drywayll) and get stuck between that and the vapor barrier, then create perfect mold conditions?
Thanks for any input, we are looking for expert advice from anyone that has it!