Hmmm ... I guess that's one way to do it.
I was never a residential igloo guy but ...
Looks good!
The house (brick) was built in 1960 and furnace oil must have been free in those days, because there is no insulation in the walls. So, I decided to put rigid foam insulation on the inside, with another layer of drywall.
Of course, houses of a certain vintage have their idiosyncrasies. The walls are not 8', they're 98-1/2", hence the strip of plywood along the bottom. The heating register was flush with the old wall, so I had to frame around it, since the insulation/drywall layer is 2" thick. Had to extend the window frame the same way.
This one small bedroom will cost about C$1000, including paint. I'll probably not live long enough to recover that in energy savings, but the room should be more comfortable.
I'll probably tackle the main bedroom in the Fall.