According to ASTM E779 - 19, what is the limitation regarding the type of buildings tested?

The correct answer reflects the guidance provided by ASTM E779 - 19, which specifies that the testing method is particularly applicable to single-zone buildings. This is primarily due to the standardized conditions under which the airtightness measurements are intended to be made. Single-zone buildings, characterized by having a relatively uniform pressure distribution throughout, allow for more accurate and consistent results when measuring their airtightness.

The standard recognizes the complexities involved in multi-zone or high-rise buildings where pressure differentials can vary significantly between different areas due to stack effect, wind, and other factors. Consequently, testing such buildings would not yield the same level of reliability or comparability in results as those obtained from single-zone structures. This is why the ASTM standard explicitly limits its application to single-zone buildings, ensuring that the results are meaningful and practical for assessing airtightness in those environments.