After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.
Garage attic insulation vapor barrier.
This acts as a barrier to keep heated moist air from rising up into the attic during cold weather.
The best approach for a vented attic in a cold climate is installing a layer of drywall with a good coat of latex paint the paint creates a semi permeable vapor barrier.
The classic answer is that the vapor barrier goes on the warm in winter side of the assembly.
In mixed climate areas the vapor barrier is optional depending on the total design of a building.
Not every wall does.
The facing on faced insulation acts as a vapor retarder.
Your first job after the studs are in place is to fill those walls with insulation.
Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers.
If you are not sure if you need insulation in your walls follow along with this flow chart.
If your garage is 45 degrees and you have a bonus room heated to 72 degrees above the garage the vapor retarder faces the upstairs room.
Attic insulation should always be installed with the paper backing facing toward the living space the ceiling in this case.
You don t mention whether there is a bonus room or living space above the garage.
If you need a vapor barrier and your insulation is unfaced you must cover it with a polyethylene film.