Cavity insulation is unique in that it applies only to old construction (or closed) walls.
To install insulation in a closed cavity, it is necessary to create some sort of opening, usually a 2 inch hole, into each of the stud bays in the area you wish to insulate. The access can be either from the interior or the exterior of the building.
Once the insulation is dense packed into the cavity, the access hole will be plugged and patched. This is the most un-evasive way to insulate your exterior walls on an existing