You are responsible for insulating part a job. How should a vapor barrier on blanket (batts) insulation be installed?

• A. Face the heated area
• B. Face the warm side of the wall.
• C. Face the cold surface
• D. Face the outside

Answer: (B)

Moisture diffusion and condensation control in wall assemblies depend on which side the vapor barrier faces. In a heated building, the warm side of the wall is the interior, where moist indoor air resides. Placing the vapor barrier toward that warm side blocks water vapor from moving into the cooler wall cavity, reducing the chance of condensation on cold framing and insulation and preventing mold and rot.

So the best approach is to face the warm side of the wall. If the barrier were placed on the cold surface or the exterior, interior moisture would diffuse into the wall cavity and could condense on cold surfaces, creating problems.