I want to insulate the ceiling in my garage. When the house was built 10 years ago, the walls attached to the house were done, and the ceiling was drywalled (Fire code). However, they did not put a vapor barrier, before drywalling. I live in Canada. Winter is about six, seven months long. I have access to above the garage. Should I staple a vapor barrier over the joices, and in between, then put my insulation?
I just want to be able to work in there once in a while, over the winter. I already put vapor barrier and insulated the outside walls. Going to heat it with a couple of ceramic heaters. The roof is well ventilated, with soffit vents, and a whirlybird. The roof is made with 2x4 trusses on two foot centres, and they used metal channeling to screw the drywall to.

First of all a garage is not a signicant source of vapor as it is not occupied that much and you don't cook or bath in in it.

And the ceiling acts as a enough of a vapor retarder. Specially with good ventalation in the attic space.

The ground here is frozen until the middle of May, then it starts to warm up. What about when the outside temperature is warmer then the temperature in the garage? Wouldn't there be vapor then. Couldn't you get condensation on the bottom of the insulation, and drywall above the ceiling?
I want to heat it so I can work in there comfortably. I have a motorcycle I want to customize over the winter.

I was just thinking about what you said Bill. It's making some sense. If the ceiling is retarding the vapor, then if you paint it with a latex paint, that would even be more of a retarder, right?