Our home is 150+ years old. Our walls are filled with urea-formaldahyde foam appx. 5 to 6 inches thick. Its currently 3 degrees here with a chill of -24. All exterior walls are warm, but where the floors meet the foundation they are drafty. We don't have any insulation in the floors between the basement and first floor. I can't for the life of me figure out how to stop or seal those drafts. The old basement walls are about 2 feet thick of boulders. The construction is weird because the homes floor joists are built in quadrants. Some run north to south and others run east to west. I think where the air is coming in is where the joists run into the beams on the foundation. I have looked over this multiple times and can't come up something to stop it. Everything else has been updated, windows and ductwork.