I have found lots of information about insulation and exterior walls.

The question I have pertains to a bathroom over an attached garage.

One wall of the 2 car garage is attached to heated space.

About 2/3 of the garage ceiling is connected to heated space.

There is a dropped ceiling below the bathroom, and it was insulated improperly. The water pipes are above the insulation, and there is about 14″ of open air space above the insulation and 31′ x 14″ of possible exposure to an un(der)insulated rim joist. The kraft facing is towards the garage (unheated but not exterior)… yes, it is easier to staple up that way. The homeowner is wondering why the pipes freeze. Hmm.

I am in Zone 5, and as I understand it, a vapor retarder may not be necessary for exterior walls.

I have not been able to find anything yet on insulating what I would term a partition ceiling. The garage, although unheated, will not normally reach below freezing temperatures unless the overhead door is left open. I would expect a 50* winter differential and maybe a 35* summer differential.

Would this ceiling cavity be insulated with the kraft facing towards the heated space, or no facing at all? 

I am leaning towards no facing, but figured it would be good to check a bit.