Which statement about the wall layer order is true?

• A. The order is interior finish, vapor barrier, insulation, sheathing and cladding
• B. The vapor barrier is outside the insulation
• C. Insulation is the outermost layer
• D. Cladding is between interior finish and insulation

Answer: (B)

Moisture control in a wall relies on placing the vapor barrier where it can most effectively limit moisture diffusion from the warm interior into cooler wall components. In typical residential construction, the warm interior side hosts the moisture source, so the vapor barrier goes on that interior side of the insulation. From inside to outside, the common sequence is interior finish, vapor barrier, insulation, sheathing, and cladding. This arrangement helps prevent humidity from traveling into the insulation and framing, while still allowing the exterior to manage moisture through permeable layers and ventilation.

If the vapor barrier were outside the insulation (toward the exterior), it would impede drying toward the interior and could trap moisture within the wall cavity, increasing the risk of condensation and damage. Insulation being the outermost layer would ignore the protective role of the cladding, and placing cladding between interior finish and insulation would misplace the outer protective layer.