celestory insulation

[sunspot]

I've just started replacing six celestory windows. I'm adding R6 Roxul Comfort Board to the exterior under rain screen and vinyl siding.
My question for the group relates to the interior.
The drywall is nasty. There is some poorly installed vapor barrier behind it. I'm wondering about covering the existing drywall with some sort of painted foam to increase insulation value and give me a lightweight, easily installed, interior finish (I'd hide the joints with trim). No fire resistance I realize. I'm also wondering about tipping the foam wall covering on an angle to provide room for additional insulation at the wall plate/rafter interface which I assume is currently a source of heat loss.
If this idea is madness please stop me now before I get very far.
Thanks,

[ecomodded]

Old post , I have an Idea the wall insulation. Install the insult on the outside of the house. Install the inside rigid insulation to your inside corners at the roof to wall joint. From the attic locked in place with a can of foam insulation.

In my cabin I will be adding extra rigid insulation on the outside of the cabiin , 0 to 4 ft then cover it with boards. So the log cabin still shows from 4ft on , with this I get extra insulation effect in the cabin at the 4ft level where it’s normally the coolest.
Doug / ecomodded