wall insulation

Here is me current situation. I have a room that is a converted garage. It has no heat and currently has no ceiling (see right up to the attic roof). I plan to put a supsended ceiling in with insulation above that.
I just insulated the exterior wall, with facing side in. I am about to redo the interior wall insulation. On the other side of the interior wall is a room that does have heat. My qestion is, do I use any vapor barrier in this inside wall, or do I just use unfaced insulation? I would assume that the heated room will be warmer than the non-heated side, not sure if it will be enough to create moisture....plus, didn't know how the exterior wall that already has a vapor barrier affected this. I have heard conflicting suggestions from workers at Home Depot on what to do. Any suggestions?
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