I own a 2 storey double bricked wall home(no insulation in the walls except one wall in the kitchen). I am considering insulating a side wall. A second storey bathroom and  bedroom on that side of the house are cold in the winder and too warm during the summer (both are corner rooms). It would be impractical to insulate both the second storey and the first storey of that wall. The simplest approach would be to add exterior rigid foam insulation and siding to the second storey, the aesthetic would not be the best but nobody can see the side of the house as it is only a few feet away from the neighbours home. Interior insulation was added to a portion of the first storey of that wall(kitchen). My question is, since I would be insulating the second storey only (the exterior insulation would extend slightly just below the second floor/joists) would the R value still improve enough for the second storey? I am concerned that not insulating the first storey would allow the cold to migrate throughout the first storey brick upward into the second storey portion of the wall. As for summer the main issue is during sunny days the wall gets really warm (it gets lots of sun), adding both insulation and light color siding will stop the sun rays warm up the brick(the brick gets really warm to the touch).