We recently remodeled the kitchen in our 1954 brick ranch and discovered only “Insulite” fiberboard insuation was used. My understanding is that is only an R-1 rated insulation, so when we replaced the drywall, we added R-15 batt insulation. My question is, how do we insulate the remaining walls of the house without replacing all the drywall? Is this possible? What's the best way?