Basement insulation
#1

I have a 1955 brick & plaster ranch house with a large cold basement. Cold air comes into basement from the perimeter where the 1st floor and joists meet top of foundation. I want to insulate between the joists but I am concerned that insulation installed where the 1st floor meets the top of the foundation will trap vapor between 1st floor plaster walls and brick. Will sealing off the air that is coming into the basement from the perimeter cause a problem between the plaster walls on the first floor and the brick?
#2
Forget the insulation for the momment. Seal the air leaks first. Use caulking -- regular caulk for small gaps and expanding foam for larger gaps. Sealing the gaps won't cause problems, and it will make a big difference -- maybe not in the temperature of your basement, but in your heating bills.