Hello, I am in the process of remodeling our 90-yr-old house. One problem we have is that the walls only have about 3 inches of blown in insulation. On the second floor we have a wall on each side of the house that has a vented crawl space (it's larger than a crawl space. Gambrel roof). So what they did was staple cardboard to the back side of the studs and then blow the insulation in. I would like to put another layer of insulation hopefully without firring the studs out. How could I do this? I was thinking about some sort of rigid board but I am not sure.