What is an essential condition for conducting a test as per ASTM E779 - 19?

The essential condition for conducting a test as per ASTM E779 - 19 is that all interior doors must be operable. This requirement ensures that the airflow paths within the building are representative of normal operating conditions. When interior doors are operable, it allows for a realistic assessment of the building's airtightness, as it accounts for the natural air movement that would occur in a typical setting.

Testing with operable interior doors helps to identify any leaks or weaknesses in the building envelope that might be affected by how these doors function. This can provide a more accurate measure of the overall airtightness of the building, leading to more effective energy use and indoor air quality.

In contrast, having the building empty, all windows open, or only closing exterior doors does not provide the necessary conditions to evaluate the true performance of the building's envelope effectively. These scenarios might misrepresent the building's airtightness by either eliminating possible leak points or creating unnatural pressure differences, leading to unreliable test results.