I'm going to blow insulation into the attic of my 100+ year house the attic has no insulation in it currently. I want to do the walls as well. My problem is when I drill a hole into the wall I only expose a cavity that is roughly 1-2" deep. Hardly enough to fill with insulation. Wanted to fill walls from attic but all rafters are notched to sit on top plate leaving no opening to walls. Is the 1-2" normal or is there something I'm overlooking?