In 2012, Red River College in Winnipeg, Canada, embarked on a program to expand the knowledge base on the airtightnesscharacteristics of commercial buildings by conducting tests on a cross section of Manitoba's commercial building stock. Thisprovided quantitative data on the performance of these buildings and offered critical, practical experience with airtightness testingprocedures for commercial buildings.

Over three years, airtightness tests were carried out on a diverse sample of 26 commercial buildings ranging in age from1 to over 100 years in age, floor areas of 150 to 19,788 m² (1615 to 212,918 ft²), and building heights from 1 to 16 stories.Using the normalized leakage rate (NLR75) as the primary metric, the measured airtightness was found to vary by a factorof 18:1 between the tightest and loosest buildings in the sample (0.19 to 3.44 L/s x m² [0.037 to 0.678 ft³/min]), with a mean of1.70 L/s x m² (0.335 ft³/min). The tightest building in the survey, a one-year-old middle school, achieved an airtightness of 0.19 L/s x m²(0.037 ft³/min), better than almost all commercial building results reported in the literature. Overall, these results are particularlyinteresting given that current standards for new construction recommend (maximum) leakage rates of 1.27 to 2.03 L/s x m²(0.250 to 0.400 ft³/min x ft².).

The study also revealed that then-current testing standards had serious weaknesses in their treatment of the building's intentionalopenings (such as HVAC inlets and outlets). Rather than employing a single sealing schedule, separate envelope and energyschedules are required depending on whether envelope integrity and durability or energy performance is of primary interest. Thisinsight was subsequently incorporated into ASTM WK35913, New Test Method for Whole Building Enclosure Air TightnessCompliance.