What primarily distinguishes two-point testing from single-point testing?

The primary distinction between two-point testing and single-point testing lies in the use of multiple pressures instead of just one. In two-point testing, the airtightness of a building is assessed at two different pressure levels—typically one positive and one negative pressure. This method allows for a more comprehensive understanding of how the building behaves under varying pressure conditions, which is particularly important for identifying potential air leakage paths and understanding the overall performance of the building envelope.

In contrast, single-point testing measures the airtightness at only one pressure level. While this can provide useful information, it does not capture the full dynamics of how the building performs under different pressures. The multi-pressure approach in two-point testing helps identify inconsistencies and potential failure points in a building's air barrier system more effectively than a single measurement can.

The other options do not accurately capture the fundamental difference between the two testing methods. Testing only at high pressures does not characterize the two-point approach, and neither does measuring at varying air temperatures, as temperature is not a direct factor that distinguishes these two types of tests. Focusing solely on leakage at one pressure is essentially what single-point testing does, further emphasizing that it is the use of multiple pressures that is key to two-point testing's distinctive methodology.