I am considering options on increasing insulation of vaulted ceilings in three areas of a customers house. It will have to be done from the inside. I prefer to leave the exixsting sheetrock and foam or nailbase panels then new t&g wood ceiling. Customer would prefer not to lower the ceiling any more than necessary . House is located in Boone NC. mountains

Greetings,

I recently upgraded my cathedral ceiling from the inside. I have a sips house, but this method will work on any cathedral ceiling.

Run 2x2 across the rafters, 16" cc. In between install Fifoils ( fifoil.com). 2 layer radiant insulation, perforated.
On the surface of the 2x2 install a single layer, ( like a vapor barrier) radiant insulation, perforated.
Install across the 2x2 wood furring strips suitable for the panel ceiling.
Total thickness about 2 1/4 " to 3" plus paneling.
Performance, about 2 btu/sf/hr according to data from Mark's Mechanical Engineering Handbook
There is no sys in this small of a space that will come close to this.
Since there is no condensation or moisture retention in this sys there will be no inherent moisture to affect the paneling.
The furring strips crossing each other reduces the conductivity path.

With no power to my house for 6 1/2 days, unshaded dark roof, 95+ deg days the house temp never exceeded 80 degs.

What is the insulation & material stack-up you 're starting with? (It makes a difference.)

And why does the customer think it needs more insulation in those areas?