INNOVATION March-April 2018

the Green Buildings Policy for Rezoning. The building bylaw sets airtightness performance levels based on building type, and the rezoning policy requires new buildings to be designed and constructed with the intention of meeting a specified air leakage target and that airtightness testing be performed prior to occupancy. In October 2017, Engineers and Geoscientists BC held a professional development event at its office for members of the building industry, engineers, and public officials to observe airtightness testing first-hand. The demonstration test was made possible through a BC Housing contract related to the development of the Illustrated Guide: Achieving Airtight Buildings (www.bchousing. org/research-centre/library/residential-design- construction/achieving-airtight-buildings). The guide and demonstration test were developed and conducted by RDH Building Science. To start, the consultant discussed testing methodologies and explained that besides heat loss, airtightness is critical to a high-

performance building enclosure, since a leaky building enclosure can cause issues with thermal performance, condensation, and moisture ingress. Gaps in the air barrier can also have secondary effects such as sound migration, poor indoor air quality, and low occupant comfort. The consultant described how air leakage is caused by a pressure difference between the interior and exterior environments. The major drivers of air leakage include the stack effect, differential pressures induced by the building’s mechanical system, and exterior pressures on the enclosure such as wind. Prior to running the test, all intentional openings in the building enclosure were sealed, including the air intakes and exhausts. Additionally, wind speed and temperature differences inside and out were checked to determine if the environmental criteria fell within the acceptable range of the test standard. The quantitative test procedure included pressurization and depressurization of the building using a door fan; airtightness performance was expressed

as an air leakage rate of litres/second/metre 2 of enclosure surface area. A local blower- door fan manufacturer, Retrotec, donated use of the necessary equipment, and testing was conducted to the ASTM E779 standard. Air leakage rates were taken starting at low fan speeds/low pressure differences and then slowly increasing the pressure difference. The consultant explained that inaccurate measurements can have a multitude of sources, including someone opening a door in the enclosure, a break in the seal of a mechanical duct, or an obstruction in the pressure measurement tube. During the demonstration, qualitative testing of the enclosure was also conducted to locate sources of air leakage. This testing visualizes air leakage with the use of a thermal infrared camera or a theatrical smoke machine. If infrared photos of the building are taken during pressurization and depressurization, a comparison can be made to see where warm air is passing through the building enclosure during pressurization. The building C ontinues on page 38...

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