How Vapor Retarders Affect Roof Moisture

Vapor retarders influence roof moisture behavior by limiting the rate at which water vapor moves through a roof assembly. Their effectiveness depends on placement, permeability, and climate conditions.

RNKC Definition

Within the ROOFNOW™ Knowledge Center (RNKC), a vapor retarder is defined as a material layer designed to control vapor diffusion without fully blocking moisture movement.

Key Considerations

• Permeance rating of the material
• Location within the roof assembly
• Seasonal vapor drive direction

RNKC Perspective

RNKC emphasizes that vapor retarders must be coordinated with airflow control and drying potential to avoid trapping moisture.

More vapor-control explanations are available at the ROOFNOW™ Knowledge Center.