What is the main function of a vapor diffusion retarder in buildings?

The primary function of a vapor diffusion retarder is to slow down the movement of water vapor through the building envelope. This is essential in managing moisture levels within a structure, as excess water vapor can lead to problems like condensation, mold growth, and damage to building materials. By effectively limiting the diffusion of moisture, these retarders help maintain a dry environment within walls and ceilings, contributing to the overall durability and comfort of the building.

In the context of a building's performance, controlling moisture is critical not just for the integrity of construction materials but also for the health of its occupants. The retarder should be installed on the warm side of insulation in cold climates to prevent interior moisture from condensing within wall assemblies.