Do you need wall insulation? The short answer, yes.
Now for the long answer:
Wall insulation is always good to have in the home. The chances are if your home was built in the 1970's or later, you have wall insulation. We hear a lot of homeowner complaints about cold rooms and drafts because "my walls aren't insulated!" Most times this is due to air penetrations from attic top plates or from the basement rim joist.
To the right, we see a thermal image of a room. As this test was performed in the winter, the blue spots are cold air infiltration caused by attic penetrations from above. You can see thin blue lines which are the joists. The reason it is warm between the joists is because there is insulation in the wall cavities. This particular home was built in 1969.
The home in the images below was built in 1947, and does not have insulation in the wall cavities.
Not having insulation in the wall cavities is obviously a concern, but we also noticed the home was not properly air sealed in the attic, knee walls, nor the basement. Without touching the walls, we reduced the homes airflow by 55% - a personal record for us - by bay blocking the knee walls, air sealing the attic, and spray foaming the rim joist. Upon completion of the work, the homeowners felt an immediate impact in comfort.
In fact, the investment to insulate the walls would be nearly as much as air sealing and insulating the attic, knee walls, and basement. Not only would it cost nearly as much, but it was not be as effective as the approach we took since the air would still escape out the attic at far too high of a rate. More importantly though, it was impossible to put insulation in these wall cavities as the cavities were not deep enough.
So what does putting insulation in the wall cavities involve? It involves drilling a hole in each cavity, then pumping insulation into the cavity, followed by plugging up the hole.
As you can see, insulating wall cavities is a very invasive process. It can provide good benefits, but we recommend addressing the attic and the basement of the home before insulating the wall cavities.
So the long answer made short: yes, you should insulate your wall cavities if you have no insulation in the walls, if the wall cavities are deep enough to be insulated, and only if you addressed your attic and basement first.