Insulation, Radiant and Vapor Barriers - adding insulation to existing cathedral ceiling

I would like to add more insulation to an existing cathedral ceiling.Currently it only has R 13 and is unvented.Should I to lower the catherdral ceiling by 12" by adding 2x12 joists an add R-38 fiberglass insulation over the existing drywalled ceiling. Or should I remove the entire ceiling, vent it and add deeper joists and add the R 49 that is recommened.I would perfer not to remove the existing ceiling either way i look at it i need to add addtional deeper joists in order to leave room for the added insulation.

I would remove the drywall, vent it then build up the studs to get the recomended insulation r-factor for your area. I think if you do not remove the existing drywall ceiling you will have moisture problems.