The picture above shows the outer walls of a house I'm modeling. The walls of the main house (highlighted orange) need to have an inner layer of insulation, which is half as thick as the present walls.
Ideally, I could create an n-gon with the selected vertices and then do an inset to get the geometry I want. However, an n-gon cannot be created from the selected vertices. Or at least, no n-gon is created when I hit [F].
Is there some way I can avoid a lot tedious vertex shuffling?