What is the purpose of vapor diffusion retarders (VDR)?

The purpose of vapor diffusion retarders (VDR) is to slow the diffusion of moisture through materials. This is particularly important in building construction and energy efficiency, as excessive moisture can lead to a range of problems, including mold growth, wood rot, and degradation of building materials. By incorporating vapor diffusion retarders into the building envelope, moisture migration is controlled, thereby improving the overall indoor air quality and longevity of the structure.

VDRs are essential in maintaining a healthy balance of moisture in building assemblies, especially in climates where the difference between indoor and outdoor humidity levels can lead to significant moisture accumulation. Effective application of VDRs helps to protect insulation and other building materials from moisture-related damage, safeguarding the investment in energy-efficient products and enhancing occupant comfort.

The other options, while relevant to building performance, do not address the specific function of vapor diffusion retarders. Promoting air circulation pertains more to airflow management, increasing heat transfer concerns energy efficiency and thermal performance, and blocking sound transmission relates to acoustic treatment in buildings. None of those functions describe the primary role of VDRs, making the correct answer focused on moisture diffusion.