My 140 year-old house in the NW Suburbs of Chicago has hollow interior walls (actually, aren't most walls hollow?). However, unlike new construction, there is no top or bottom 2x4 to my framing, which means the walls are hollow and open all the way from the top attic to the bottom basement. This is great if I need to run new conduit, but the Knob & Tube was replaced 15 years ago, so I'm pretty well set.
OK, here's my question: Should I worry that the walls are open at the top? Should I seal them some how? There is no insulation in the walls. Is it necessary to blow in fiberglass insulation, or use the new foam insulation (for a higher cost to me). The walls are all lathe and plaster, so they are very quiet - I'm not worried about sound problems. Also, since they're not exterior walls, I'm not worried about heat loss from one room to another. Should I worry about heat loss or moisture problems in the attic?
Someone suggested jambing R13 insulation batts down each joist opening, and then sealing the top with plastic, or putting some loose fiberglass insulation inside a plastic bag, and forcing that down between the joists. Then cover the top with more loose insulation.
What's your opinion - do I insulate the entire wall cavity, or just stuff and seal the tops, or just ignore the entire process and not worry!