Hello! Alan here.  I have read many postings online and many link to this site. I have a 1930 colonial with slate roofing.  The attic area is vented with lower gable vents on both sides of the house. There are no box vents, soffit vents, or ridge vents. The decking is 1×3 straps (gaps in between) with slate overtop paper.  I am planning to use mineral batts and leave a 2-3” air space between the batt and decking.  On the front and back of the conditioned (front and back of house) is cold storage (insulated ceiling joist and no insulation on roof framing.  The conditioned space would be between these two cold storage zones.

Two questions.

1. if I have low gable vents on both ends. Considering adding a fan to pull air across the house so fresh air enters one side and is evacuated in the other pulling air across the roof assembly. Is this enough air movement?

2. I was considering not creating and air chase in each cavity with a baffle (either pre made or onsite) but that an air chase as I explained above would be inherent with the mineral insulation as it will not be pushed against the roof deck.  Is this acceptable? I plan to use 1” rigid foam for thermal bridging under the roof assembly taping all joints.

does this sound like a good plan and does this seem to preserve the integrity of the assembly?

Thanks!
Alan