In standard kraft-faced insulation, the vapor barrier must

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

Answer: (A)

Controlling moisture movement through a wall is the main idea. In standard kraft-faced insulation, the paper facing acts as a vapor retarder, so it should face the heated interior side. This puts the moisture barrier on the warm, humid side where interior air is pushing moisture into the wall. By placing the barrier toward the interior, the diffusion of moisture into the wall cavity is slowed, reducing the chance of condensation on cold surfaces, which can lead to mold or rot. If the barrier faced the outside, interior moisture would diffuse into the wall, condense there, and dry poorly. So the orientation toward the warm interior best protects the wall assembly.