If installing in a garage do you need to install a vapor barrier?

A vapor barrier is only required when the application involves an exterior wall and is required by code. Meant to block water vapor transfer from the warm side and condensing on the cold side of the wall. If you are using this, always attached to the warm side. In terms of what material to use, poly may not be the best option. Poly is very impermeable. A couple of other options are vapor retarding latex paint on the drywall or smart vapor retarders