What is defined as a vapor retarder?

A vapor retarder is defined as a material that helps to limit the amount of moisture vapor that can pass through it. The permeability range provided in the correct answer—0.1 to 1.0 perms—characterizes a vapor retarder effectively. Materials falling within this permeability range can slow down the movement of moisture vapor, thereby reducing the risk of moisture problems within building assemblies.

The concept of vapor retardation is crucial in building science, as excessive moisture in walls or ceilings can lead to issues such as mold growth, wood rot, and damage to insulation. A vapor retarder helps manage moisture control without completely blocking vapor movement, as is the case with a vapor barrier, which has very low permeability.

Understanding the role of a vapor retarder in terms of its permeability allows builders and building scientists to make informed decisions about materials and construction methods to enhance the durability and effectiveness of buildings in various climates. This understanding is essential for successful airtightness testing and ensuring that a building performs well in terms of energy efficiency and moisture management.