what is best insulation for exising interior walls?
Answers:
I have two comments. First, if you follow "LYN'S" advice, you may very well do structural damage. The insulation he's talking about is meant to be blown into the wall cavity BEFORE the walls are finished. They spray on a layer about 1/2" to 1" thick. Once it expands, they trim the excess off with a large tool that resembles an old misery whip. I think probably cellulose fiber is going to be your best bet for the walls. The contractor drills small (relatively) holes in the exterior into the air space and blows cellulose fiber insulation in. No itch, and DOES NOT support combustion. Also consider the attic. You will have to install vents to allow air flow when you insulate your attic, which needs to be done in order to get the most bang for your buck and to eliminate any possible moisture problems.
Other answers:
Shredded newspaper insulation, environmentally friendly
Shredded newspaper insulation, environmentally friendly
Your exterior walls should already have fiberglass bat type insulation. Typically, homes built in the 1960s had 2X4 inch stud walls with 4 inch fiberglass insulation between the studs (R11 insulation rating). Your attic insulation is the most important for energy efficiency and should be at least 6 inch fiberglass or equivalent R value. Most of your exterior wall heat loss is through your windows.
Blown in cellulose insulation for the exterior walls. Not sure why you would want to insulate the interior walls.
You can have someone blow in expanding foam into the wall cavities if you want. It is very energy efficient. It can be somewhat expensive, but it is the best option if you aren't doing extensive remodeling. You should check your attic first though. Depending where you live you should have as much as 12" of insulation. Blow-in fiberglass works best for this. There are a few other things to remember to make sure your house is energy efficient. If the windows are single pane glass you will want to look at getting replacement windows. Pella, Hurd, and Marvin are some really good brands. It is also important to have good ventilation in your attic. Make sure you have some vents in your soffit and on your roof.