Answer: That's a good and frequently asked question. The answer is: "It depends."

In heating climates, the vapor retarder is generally placed so it faces the "warm-in-winter" side of a wall or ceiling. In an unheated or unconditioned attic, that means the side with the vapor retarder is placed down toward the living space below.

Building codes in high humidity climates, however, may require the insulation to be placed so the facing is away from the conditioned space. In some cases they do not recommend a faced insulation. This varies from region to region. Since you live near the Gulf coast, we recommend checking with your local building department for the requirement in your area.

Another consideration is whether your attic already has insulation. If you are adding insulation in the attic the original layer may already have a vapor retarder facing the living area of your home. If you add a second vapor retarder with another layer of faced insulation, any moisture that does get through the first layer may condense on the second.

Install the second layer on top of the first layer, between the joists, unless the joist cavity is full. In that case, install the second layer perpendicular to the first layer, covering the ceiling joists to reduce heat loss through the wood.