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David Bohac, Martha Hewett, James Fitzgerald, Joshua Novacheck, and Andrew Lutz
Bibliographic info:
The International Journal of Ventilation, Vol. 12 N°4, March 2014

This paper presents results from whole building air leakage tests used to document the leakage reduction due to envelope sealing and assess the accuracy of contractor's estimates of the impact of their sealing. The measurements also compare the differences in envelope leakage reductions determined from depressurization versus pressurization tests and determine mechanical system leakage.

The eight buildings were constructed between 1936 and 2007 with floor areas that ranged from 1100 to 22900 m2. The buildings were relatively tight with normalized air leakages that ranged from 2.66 to 7.41 m3/h·m2 at a 75 Pa pressure difference. Six of the buildings were air sealed with work that focused on spray foam sealing of accessible wall/roof joints and upgrades of exterior door weatherstripping. The sealing reduced air leakage from 6 to 17% with a median of 9%. The measured leakage area reduction was only 4% to 24% of the contractor bid estimates of leakage they would seal. Post-inspections indicate that the lower measured reductions were not due to incomplete air sealing, but an inability of the contractor to estimate the amount of leakage they would seal.

There was consistently higher leakage under pressurization than depressurization. The ratio of pressurization to depressurization tightness for the pre and post sealing measurements varied from 1.12 to 1.31 with an average value of 1.21. The mechanical system leakage ranged from 0.57 to 3.78 m3/h·m2 and increased the envelope leakage by 17% to 103%. This suggests that mechanical system air leakage can have a significant effect on building air leakage when the systems are off.