What is the function of a drainage plane behind masonry veneer, and how does it relate to air barriers?

• A. It blocks moisture entirely.
• B. It allows moisture drainage and helps keep interior dry; it works with the air barrier to control moisture and air infiltration.
• C. It serves only decorative purposes.
• D. It reduces structural capacity.

Answer: (B)

Moisture management behind masonry veneer relies on a drainage plane to provide a path for any water that gets behind the veneer to drain downward and out, while also creating an environment that allows the wall to dry. This layer often works with a spaced or ventilated gap that helps moisture evaporate and move away from the interior.

It also relates to the air barrier because the air barrier controls the movement of air through the wall, reducing air-driven moisture intrusion. When the drainage plane and the air barrier work together, bulk water and moisture-laden air are kept from penetrating into the interior of the building, helping to keep the interior dry and the wall healthier.

So, the drainage plane is not about blocking moisture entirely or about decoration, and it does not alter structural capacity. Its job is to drain and dry behind the veneer, in concert with the air barrier that limits air movement and moisture entry.