With a blower door depressurizing a house to -50 Pa, what does a pressure of 0 Pa in the attic indicate?

When a blower door test is performed and the house is depressurized to -50 Pa, the pressure of 0 Pa in the attic indicates that the attic is at the same pressure as the outside environment. This scenario suggests that the attic is effectively part of the home's pressure barrier.

In a well-sealed structure, areas that are fully within the pressure barrier should experience the same pressure as the interior of the house when it is depressurized. A reading of 0 Pa shows that the attic has not been affected by the depressurization of the home, implying no air movement into or out of the attic space at that moment. This often means that the attic is adequately sealed, maintaining an effective boundary between conditioned and unconditioned spaces, which is crucial for reducing air leakage and enhancing energy efficiency.

This reading is important for understanding how air is managed within the building envelope. A reading of 0 Pa does not suggest any over-ventilation or leaking issues since it indicates stability in pressure relative to the external environment. Thus, confirming that the attic resides comfortably within the pressure boundary of the house aligns with the principles of maintaining a controlled indoor environment.