OK, now I understand. I would use only pressure treated or metal structural support and styrofoam for insulation. Then, green wallboard (moisture resistant). I would install it with screws, but not tape the seams. Cover the seams with a nice piece of wood trim which could easiy be removed accessing the drywall sections. Would only be necessary to locate the screws for the center studs for the section when removing one. As for an entirely removable section, I believe it would be necessary to attach the drywall to plywood or another surface. My concern, based on the conditions you describe, is that the plywood would warp and ruin the wall. Another thought - install a flush door (either hinged or a door panel) where the problem areas need inspection. Hope this helps a bit.

Cute little devils, aren't they? The two inches of mice droppings are actually probably bat guano, not mouse droppings. Very good for the garden, though, full of nitrogen. You can shop vac them up (the droppings, not the bats!) and it will clean up and leave less smell residue than mouse droppings as there is usually less of a bat urine smell (maybe they pee outdoors on the wing), unlike mice who pee where they poop. Once you've got them removed, you'll need to do a meticulous job of re-sealing of even tiny cracks or other bats will find your attic and re-colonize. So, before they are removed study the exterior well to see where they are entering; this is best done in the evening and very early morning when they are returning from a night's bug-catching. But you will have to look for alternate holes as well, as they are really fixated on their roosts and return year after year to the same ones. Depending on where you are, you can also just wait for them to leave for their winter hibernation dens, then seal the walls up to prevent them from coming back next spring. That would save the cost of a bat-removal. Another thing you might do is provide some bright lighting to the area at night through sunrise. Bats like to sleep in the dark and you might discourage them from coming in to roost. But make sure it's safe lighting that won't cause a fire. Bats eats zillions of biting bugs every night, so removing a large colony will change the bug dynamics at your place. But on the other side of the coin, bats can be vectors for rabies, and it is possible for sleeping people (especially young children) to have contact with rabid bats and not realize it until too late. If you should find a dead bat in a sleeping room, contact your doctor and health department immediately. On the whole, bats are nice, useful, critters. I have tons of them in my barns, and even my attics. (I reluctantly tolerate them there, but would rather they stayed in the barn.) They all fly off somewhere for the winter; I'm not sure how I would feel if they were around 12 months of the year. After all the bats are gone, you can look and see if any insulation must be replaced. The good thing about bats is that the dropping piles are usually fairly concentrated so you won't have much too much to do. There are some great books on bats. Looking at pictures of them will scare the bejabbers out of you, though. I lived for many years in areas with large (14" wingspan) fruit-eating bats and medium sized vampire (biting) bats, so the much smaller ones in North America seem pretty tame. Though I hate having one flying around in the house! Just keep thinking of the thousands of mosquitos and black flies and biting gnats they eat every night.....! It's surprising you had two inches of droppings, that takes awhile to accumulate. Fifty years ago, when I was a young girl, my family spent a fair amount of time at Angkor Wat in Cambodia. In those days it wasn't a big, international tourist attraction and one could wander pretty much at will through the various temples. My sister and I sometimes clambered up over piles of bat dung a yard or more high to get into some of the buildings. Now that's a LOT of bat poop! And man, did it stink in that heat....! Molly~

Great information. Your're right and you know your stuff. I'm in eastern Ontario. thank you. The headers will be at 3.7in with a rocksol cover, so at or above code. The reasoning for the concrete walls is that most if not all condensation happens on the top 2ft of wall where it's coldest and a dewpoint is reached. The 2in of spray foam (Gynex) of that top 2ft of wall will provide the air barrier I seek, and should stop all condensation. Which would spray overlap with the black tacky tarp remaining on the wall below it. Then with a pink bat fiberglass at R14 covering over the entire wall from top to bottom, it will provide that addition R value at the top and also the bottom. So a great thermal barrier. Then an additional poly cover from top to bottom again to provide an additional vapor barrier. I have a extra fresh pink insulation to use so there's no extra cost. I just have to by a small roll of poly and tuck tape and some labor on my part to re-install. Yes to 24 hours out of the house for full cure. I'm doing this partial "flash and batt" because I think its the most cost effective way. Is this reasoning good? Are their still risks to developing condensation behind walls? Should l get spray foam down to 3 feet?

Above is the before picture. I'm discussing e.g. the wall in the background in the upper left. The top part of the wall is above grade, framed, insulated, and has plastic sheet over the insulation. The bottom part of the wall is below grade and concrete below the framed wall. The insulation is held up against the concrete with some sort of breatheable fabric, there is no furred wall in front of the concrete. Above is an after picture taken of that same wall, but standing in that room (same angle as first picture would be blocked). A furred wall has been framed an inch or two in front of the concrete and goes floor-to ceiling. In some places of the basement the existing insulation that was hanging against the concrete was saved and reused. In this particular area new insulation was put between the studs. I think it is R-19. And it is the same thickness all the way up, so there also isn't any additional insulation for the inch or two lip where the concrete is wider than the above ground framing. I can't get a picture of it now without removing the new vapor barrier, but when I posted the question, the old vapor barrier was still on the top framed part of the wall and they just put the new insulation in front of it. They might have scored it, but I don't think so.