I am planning on insulating an older two car detatched garage that will be covered with half inch plywood. I am pretty sure it would be wise to put up a vapor barrier around the walls but do I need a barrier between the plywood and insulation on the ceiling? I live in southern Minnesota and only plan on heating garage for oil changes and such.
Why would you do wall and not ceiling? It would be wise, considering the small cost and time investment. It doesn't take much heated air in our cold winters to result in substantial moisture condensation.