My brick house was built in 1928. I had to remove a wall due to a plumbing leak, and I was surprised how much open space there is in the house! (No wonder there is a problem with pests).
The wall that I removed had a plasterboard on the inside, then there were 2x4 studs that were backed (on the outside) by more plasterboard, then roofing felt on the outside of that, another airspace, and then the brick.
Before we put up the replacement drywall, we put fiberglass insulation between the 2x4 studs. This wall is 8' x 8'. I can't afford the aggravation, mess, and expense of doing that on any other walls! The plaster walls get very cold in the winter (winter temperatures are usually below freezing, and a couple times a year below zero).
Should I insulate the house? We do have a problem with brown marmorated stinkbugs (a new imported pest) and now that I understand how a house is made (with vents on the brick to let moisture out) I understand why so many in my living space, they are probably hibernating in all that empty space in the walls! Yuck!!
Perhaps the best thing to do (with respect to the bugs) is seal up any holes in the plaster where the bugs might be getting through from the air space where they live, rather than sealing up holes under the eaves and such (as was recommended in an article by Penn State), so I got some expanding foam sealing to put around the outlets, where the cable wire comes in the house, etc. -- though I don't think I can find all the holes the bugs come in at!
Then I was thinking about using the expanding foam to fill the air space between the studs, to insulate the house. I've read on other posts that these old houses are designed to breathe, and I don't want to do anything that would cause future repairs! Also I've heard that it's better for my family heirlooms (old wooden furniture) to be in a house that breathes than in a tightly-sealed house.
If you think I should insulate this house, how would you recommend doing it?
I have no idea just how the walls could be insulated, but I think you will find that it is more of a job than you want to take on yourself. Several years ago, I wanted to blow insulation into the attic of my shop. I priced the insulation and thought I had a real deal because the dealer selling the insulation would give me free use of the blower. Before I took action, I called a professional insulation company for a price. I just wanted to see how much I was going to save by DIY. Ha! I learned that they would sell me the insulation and do all of the labor to install for a few dollars less than just the insulation was going to cost me. Now this was just an attic, not walls, but my point is, this might well be something you would want the pros to do. At least get them to give you an estimate.