The building leakage curve, a product of a blower-door test, shows expected leakage rates of a structure at specific pressures. We’ll get into how this can be helpful in a bit. Automated blower-door testing using software from a blower-door manufacturer (either Minneapolis Blower Door or Retrotec) will calculate the building leakage curve. Previous generations of the tool required manual inputs and calculations to produce the graph.

The most accurate, and in my opinion, easiest method to create the building leakage curve is by conducting a multipoint blower-door test. This type of blower-door test collects data at several different pressures during the test, as compared to the single-point test, which only collects data at one pressure (usually 50 Pascals). The multipoint tests used with the software are standardized test methods, typically the ANSI/RESNET/ICC 380 standard, or ASTM E779 standard. Both standards, plus ASTM E1827, are accepted by International Residential Code (R402.4.1.2) as air-leakage testing methods. Canadians might use the CGSB testing standard, which also has a multipoint test option. (An interesting footnote to the single vs. multipoint test using the 380 standard is that if you choose to only perform a single-point test for code-compliance blower-door testing, 10% must be added to the final blower-door test result. If the final result is above 2.72 ACH50 and the person performing the test uses a single-point test method, the test fails for areas requiring a maximum of 3 ACH50.)

For this discussion, we will go over the ANSI/RESNET/ICC 380 multipoint airtightness method. The 380 standard requires the multipoint test pressures to be a 10-second average (typically more than 100 data points are collected during the 10 seconds of data recording) of five equally spaced pressure points between 10 and 60 Pascals (Pa). Software I’ve used will take the pressure readings at 10 Pa, 23 Pa, 35…