What Is Excessive Negative Building Pressure?
The HVAC system inside a building creates negative pressure when it draws in more air from the return ducts than it puts out through the supply ducts. Excessive negative pressure can cause outward-opening doors to be difficult to open and then to slam shut as well as prevent inward-swinging doors from fully closing. Excessive negative pressure can cause outside air and the moisture it contains to be drawn through the components of the building envelope and can lead to mold growth or other excess moisture-related issues. In the extreme, excessive negative pressure can even draw rainwater through the building envelope into the interior.
Buildings cannot (and should not) be absolutely airtight. However, the more locations in a building where air flows freely, the more locations moisture incursions can occur. Combine multiple free airflow locations with the presence of negative pressure, and no manner of sealant applied to an area that exhibits leakage will prevent air and moisture from entering free airflow building envelope locations.
In Part 2 of this Excessive Negative Building Pressure series, we explain why metal buildings are more likely to be challenged by issues related to Excessive Negative Pressure. In Part 3 of this Excessive Negative Building Pressure series, we share some solutions to solving excessive negative building pressure challenges.
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