Bathroom remodeler here.  I have a client who has severe ice damn issues in their master bathroom.  There are vaulted ceilings which have peeling paint and clear signs of moisture.  We are in the Chicago area.  Part of this is due to vents being installed on a side wall vs the ceiling (since it’s vaulted).  

2×10 roof structure with batt insulation.  Client had rafter vents installed but it’s not nearly enough.  

My suggestion to him was to have a roofer add a second roof structure overtop of his existing roof in order to give him an air gap.  He doesn’t want to do this.  

His thoughts, which I’m hesitant to back, are to add a separate ceiling to the bathroom that opens up more area in the attic allowing for more insulation.  I don’t like the idea of a ceiling structure hanging on ledgers around an entire room.   There would actually be no ledger on the sloped wall.  

Am I right to advise him against this?  I’m not a framer so structural changes are not my area of expertise.  This is something that I would bring in an outside engineer for but I want to know if it’s even worth thinking about.