Large Building Air Tightness Testing

Large Building Air Tightness Testing

 

Written by: Rick Miller, Service Organization Manager

Over the years, the need for higher performance buildings has helped to develop design changes that include a more efficient use of energy and resources. More and more, designers and builders are showing an increased interest in knowing the actual air tightness of the projects they are involved in constructing as a way of better calculating the building’s energy performance. This allows for more accurate expectations of how the building will make use of its energy inputs and will also allow for more accurate design engineering of the building’s mechanical systems.

There are several test standards and protocols currently in use across the globe. These provide for different targets of air tightness and different metrics used to report the results. One of the best ways of comparing the relative tightness of buildings in relationship to their size is by measuring the amount of leakage at a standard pressure, and comparing it to the conditioned interior volume of a building. A common standard in commercial buildings would be Cubic Feet per Minute at 75 Pascals pressure or CFM75.

In the US, one of the more stringent targets is set by the Army Corps of engineers or the USACE. The standard used here is for a building to achieve 0.25 CFM@75Pa / sqft of envelope area. In this case, envelope area is calculated by using the sqft of all four walls and includes the ceiling and floor areas as well. Here in Canada for the last 20 years, the National Research Council of Canada has suggested that air leakage over a commercial building’s envelope be limited to 2 lps/m2@75 Pa or 0.4 CFM @ 75Pa / sqft.

Using the CGSB-149.10-M86 protocols for the determination of building envelope air tightness, fan depressurization is used to collect multiple data points and also adjusts for indoor/outdoor temperatures. Using this method, the air change rate per hour (ACH), can also be calculated. There is also another metric that can be calculated from this type of testing, which can indicate if the leakage is from a few large holes in the envelope, or many smaller ones. This is helpful information when it comes to searching for the suspected areas of leakage.

Although not yet code, the trends towards air tightness testing being required are ever increasing. It may be for an energy program, or driven by owners who want more efficient buildings, or because it actually becomes part of the building code. Over time, airtightness testing on a regular basis will also help Architects and contractors learn what does and does not work in designing and constructing energy efficient commercial buildings. Knowing where the leaks are, and being able to minimize them, will also help in improving other elements of the building, such as indoor air quality and noise reduction.

Currently, all components of a commercial build are measured and verified before they are fastened into place. Airtightness testing is an added measurement available to help ensure best practices and the best finished product possible. Barrier Sciences Group is a measurement and verification company that specializes in blower door testing for both residential and commercial buildings, so whether you’re building or simply renovating, call the experts at 1-866-333-3920.
 

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