I have just replaced the cathedral ceiling, structure and all in my living room. The contractor built the structure so that moisture was trapped in the space between the decking and the drywall. Rafters began sagging over time and decking rotted away. I have now completely removed the roof structure and replaced. I replaced with 2x10's and put 16" OC. I have placed styrofoam baffles from the eave to the ridge in between each of the new rafters. However, I could not get baffles made for 16" oc so I cut the 24" inch ones in half. That leaves a small area of exposed decking on each side of the baffle. I cannot get the high density insulation available for cathedral ceilings that leaves a one inch air space.
Finally my question??? Will I have problems if I use the 9.5" R30? It will possibly contact the decking in that area between the baffle and the rafter. I do not want a repeat of my earlier problem.