Vapor Diffusion

Vapor diffusion is perhaps the most misunderstood moisture transport mechanism. Consequently, questions and concerns about vapor barriers remain the most prevalent moisture control issues in residential construction. This lesson sorts out the confusion and provides clear recommendations.

Learning Objectives

At the conclusion of this lesson, you will be able to:

• Explain the difference between a vapor barrier and a weather barrier
• Describe the relationship between permeability and temperature
• Explain how dew point is measured
• Identify where to place vapor barriers in a wall assembly
• Rank the importance of diffusion relative to air leakage in a typical home

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