The Need to Control Airflow
January’s LAB Event featured Jonathan Smegal discussing airflow – why it is important, how to control it, and what happens when you don’t. In particular, he focused on condensation and moisture-related damage.
As Jonathan explained, air leaking through an assembly can carry moisture – and that moisture will condense and potentially accumulate if it meets a cold surface (i.e. a surface below the dew point). Indoor pools in cold climates provide an extreme case to illustrate this process. High interior RH, warm interior temperatures, and significant driving forces such as HVAC equipment and stack effect can drive substantial amounts of moisture through small defects in the air barrier. Damage can develop quickly and can be extensive: Jonathan described examples of masonry deterioration, efflorescence, rust stains, mold, crumbling, and saturated assembly materials.
In a home or office building, small defects in the air barrier are not as critical. However, they can still result in mold and can also produce drafty, uncomfortable spaces, poor indoor air quality, and wasted energy (from leaking conditioned air and from adding moisture to the air that must be removed by the HVAC system). For larger and more complex buildings, Jonathan recommended clearly assigning responsibility for the air barrier to a specific person or team, to ensure that drawings and specifications are complete and that the air barrier is not compromised during construction.
Here is a brief excerpt from the presentation:
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