I recently had a new roof put on, they removed the old 2 layers all the way down to the sheathing and I missed my chance to do anything green to it then. Sheathing was over 100 a sheet and I didnt have the money at the time. 

Half my house is cathedral ceilings and the other half of the roof is open with stairs to a loft with knee walls.

The roofers installed a ridge vent however the last homeowners seem to have packed inside the loft roof (from inside the knee walls I look up and see fiberglass batts stuffed up in the drywall ceiling from the looks of it).

In that kneewall area there is some flooring and what looks to be fiberglass batts underneath. The roofing from everywhere else from the kneewall doors to the lowest part of the roof is not insulated in those rafters.

If the kneewall opening was this letter “L” the right side of the L rafters are uninsulated.

I just insulated my 97 year old home walls with mineral wool batts and am going to wrap it in 1″ mineral wool with a rain screen outside and fiber-cement siding. 

How should I address the inside roof and insulating it and correcting it if needed?

Should I reach in the knee-wall space and try and pull out all those fiberglass batts  above the loft so my ridgevent can function? Should I crawl to the edge of the roof in the knee-wall and make sure nothing is blocking the last 2″? How can I keep the loft warm in the winter and cool in the summer? Ice dams are a thing for me before I insulated the house and unsure of now until winter. 
Can I add rigid mineral wool to the cathedral ceiling and then drywall over them , assuming id have to add 2×2 blocking to current rafters inside the cathedral ceiling to get more insulation in there, or could I just add a huge mineral wool batt in there and drywall over it with the 2×2 blocking ?

Thank you