Vapor Barriers

I have a layer of insulation with a vapor barrier in my attic. I want to add another layer of insulation on top of the vapor barrier. Can I do this?

The vapor barrier should always be on the bottom. The way you have it set up now is the worst possible scenario. The vapor barrier is holding moisture in the layer of insulation below and that vapor barrier is exposed to the cold side of the attic. This will result in moisture buildup. You should flip the order so that the vapor barrier is on the floor and the insulation on top. Since you already have the insulation on the bottom, there is one possible solution to your problem. If there is the space in the attic, install double the amount of insulation on top of the vapor barrier. If the barrier remains warm, you should be safe. It would be best, however, to reverse the order of your setup. Keep the vapor barrier on the "warm in winter" side.