What is meant by the term “negative pressure” in building performance?

The term "negative pressure" in building performance specifically refers to a situation where the internal pressure of a building is lower than the external pressure. This difference in pressure can lead to various airflow dynamics within the building, causing unconditioned outdoor air to be drawn inside through any available openings, such as gaps around windows or doors.

Negative pressure can contribute to air quality issues as it may pull in pollutants or moisture, affecting the indoor environment. It often results from mechanical ventilation systems, exhaust fans, or other factors that remove air from the building, creating an imbalance between the interior and exterior pressure.

In contrast, positive pressure occurs when internal pressure is greater than external pressure, which can help limit the infiltration of outside air but can also lead to air leakage if not properly managed. Factors that could lead to a lack of airflow or an overly airtight building do not define "negative pressure," as they do not specifically refer to the relationship between internal and external pressures. Understanding this concept is crucial for optimizing building performance and ensuring proper ventilation and indoor air quality.