Yes, you can insulate so long as you do not cover any open ventilation openings built into the foundation.

I would use unfaced bats as great an R Value as can fit between the studs.

I don't know of any way to insulate the void behind your drywall short of removing it.

The ideal solution is to remove enough ceiling drywall to expose the uninsulated areas. Then have the rim joists and the gap professionally sprayed with open or preferably closed cell polyurethane foam, e.g., BASF Walltite. Then replace the drywall for fire safety purposes.

You can also use your method of batts (facing to the inside), then fill the drywall to block gap with handheld polyurethane sprays. But you will find spraying up while holding the cans upside down a very awkward, ineffeictive and messy job. I've tried it!

All vents, if any, should be sealed! If you need fresh air, equip your heating system with an HRV

I think getting the spray foam applied is the best option, since it will also seal any air leaks (very important), and it won't retain moisture like standard insulation. Supposedly standard insulation can hold moisture there and lead to premature rotting.

I insulated ours by applying blocks of solid extruded foam, and then foaming the gaps and edges. Very time-consuming. Next time I'm going to have it foamed instead, or buy a batch and do it myself.

BTW, the canned foam is not "great stuff", but a pain in the butt. The nozzles break too easily and you end up foaming yourself and ruining your clothes.

Wow! I really appreciate your thoughts.

fnmroberts: "do not cover any open ventilation openings" Just want to make sure I understand. We do have a cold air return on the outside wall that I want to fill/stop the 1" - 2" gap at the top of the cinderblock and drywall. Right now, cold air shoots up between that void actually blowing cold air into the room. Is that the open ventilation you meant?

worthy/homebound: I would give the professional spray foam option an A+. I even looked into a DIY option but backed away cause it has a high screw up value for me. I won't go into detail about our lack of cash (think orthodontics/root canal and crown) at Christmas ... so, can I get a "B" grade by filling in that void and then use an R-19 or higher insulation? Has anyone used Safetouch insulation?

I had to laugh at the "holding the cans upside down" and how "great stuff" is not. I watched my husband create some wild abstract art with that stuff. I'm actually using this daptex insulating foam when I can reach the gaps I'm finding. It actually does clean up with water (I used a pipe cleaner for the straw), has a reasonable flow, and I've used one can several times. Downsides: long shaking, the end of the can loses some discharge power, becoming a contortionist on a ladder to fill gaps like worthy.

Thanks again for helping me problem-solve. Sorry this is so long -- Once the drywall's back up, that's it.

Cathy in SWPA

Here is a link that might be useful: old house - daptex foam insulating

cathy_in_pa
No, some foundations on older homes had vents built into the foundation to exchange air from a basement or crawl space. If you have any of these, don't block them - unless they are sealed outside first.

We do have a cold air return on the outside wall

A cold air return is part of the HVAC system consisting of ductwork and registers into parts of the home. Is this what you're talking about? Or simply some kind of venting from the outside directly into the basement, as
fnmroberts describes? If it's a vent from the outside, it should be sealed as fnm says.

For a house I built in 1990, I was required to include an 8" duct from the outside directly to the furnace room and exiting over a small baseboard heater. In effect, this was a primitive HRV that I am sure future generations of homeowners will puzzle over!

I could be a puzzled homeowner, worthy. The electrical wiring has me developing hives. BTW, fnm, I enjoyed the pictures of your finished basement (and the rocking chairs:)

I'm sorry I wasn't clear about the cold air return. The return register is in the living room (outside wall) directly above the basement and is part of our HVAC system. Not to share what may not be per code, but there is no metal ductwork per se ... the cold air return is just the space in the basement ceiling between the floor joists. I did foam some gaps in that area, so now the air doesn't blow out of the register when the furnace is off. It's extremely dirty in that cavity, however.

Thanks again and sorry for the confusion:) We're doing some more work today, although my husband had to take my son golfing:)

Cathy in SWPA

cathy_in_pa

OK, from your most recent posting, I understand your heating system. It is an old style which originated with gravity heat where the cold air was captured from the outside walls and the hot air entered at the center of the home. This permitted short and steep hot air rises. Newer systems "heat" the outside walls using a fan to distribute treated air through ducts directing warm air to the ourside walls near windows then capturing the cold air in the center.

When your budget permits, have your system updated with all new ducting - the house will be more comfortable.

Glad you found the photos. Hopefully a couple useful ideas contained amongst them.

The electrical wiring has me developing hives. Literally?

Those floor returns were used right through the 1950s here. To this day, cold air returns are allowed without ducting though there can be substantial heating losses.