Old Home - Basement addition insulation vapor barrier question
This is my first time here. I recently bought an old house (1870) in Connecticut. The location has good drainage and although there are no water problems in the basement, it is damp due to half dirt floor.
My question actually relates to a basement addition, so not part of main basement with the water and home heating systems.The new basement section in effect extends the existing basement, and has a half bath and laundry room above on first floor. The space is maybe 7ft high and the room is 9X14. The floor is completely dirt at present, but I intend to throw a concrete slab.
The house came with insulation in this section but not in the main basement section. The insulation was inserted under the first floor (so on the basement ceiling in this basement addition room) with the batting facing on the outside (so not against the upper first floor section/heat, but rather facing the basement floor), which I believe is incorrect as the facing should always be toward the heat source? The seller removed part of the insulation and reinstalled it the same (incorrect?) way. I pulled the rest out and now have some faced and some unfaced batting to use.
So my questions are:
1. Does this section need to be insulated? As it is separate (with a door) from the main basement section. From what I have read it is not worth while to insulate the main basement section.
2. If I insulate it, do I need a vapor barrier? I bought a 3.5 mil plastic roll. My concern is water vapor being trapped within the floor boards. Can this happen?
3. If I need a vapor barrier, is it ok to have both plastic sheeting and a faced batt together (right against each other)? or should I just use the faced insulation batts and then use the plastic sheeting where I have unfaced batts?
.... or do I need to rethink this whole thing, haha???
I look forward to some feedback - i hope I have not asked too many questions in one.