Air leakage is responsible for a host of building problems: high energy bills, poor indoor air quality, occupant discomfort, wall deterioration (which is often concealed), and a higher carbon footprint. Until recently, owners of large buildings had few options at their disposal to test air leakage performance of their building enclosure (walls and roof) in a quantitative way.
Today, advanced technologies – a combination of sophisticated computer software, blower doors, pressure gauges and infrared imaging – is making it possible to actually measure full building air leakage performance, and start to pinpoint where the leaks are coming from. This information enables building owners to make informed decisions resulting in more efficient and durable buildings.
Case Study: The Ontario Association of Architects Headquarters
These new technologies were recently put to the test at the Ontario Association of Architects (OAA)’s Toronto three-storey headquarters where architect David Fujiwara is managing the Association’s building energy review and maintenance plan. As part of Fujiwara’s mandate to improve energy efficiency at the 20-year-old building, he engaged Halsall Associates to evaluate building enclosure air leakage performance.
Working with Building Science Corporation (BSC), Halsall conducted full building air leakage testing using a series of automated blower doors and pressure gauges controlled by a central computer. Halsall also used infrared imaging to scan for the source of air leaks. The testing was performed under the watchful eye of 30 guests, including OAA members, councillors and staff, who were invited for a first-hand demonstration.
How the test works
To test for air leakage, it is important to create a pressure-controlled environment. This means blocking off intentional openings in the walls and roof, that is, closing operable windows and doors, sealing air intake and exhaust vents, and shutting down all the building’s mechanical equipment. This preparation work is a big part of the process and results in trapping yourself – and in this case our 30 guests – in the building. Luckily, the first stage of testing took less than an hour and everyone survived the “lock down.”
Once the building is prepared, the testing works by using blower doors to force air in to, then out of, the building. This creates pressurized and depressurized scenarios which are then measured and logged. As the wind can affect building pressure, a baseline wind reading is taken on all the elevations before starting the test, in order to correct for wind effects.
The blower doors maintain a constant pressure within the building relative to the exterior. Since the building is not perfectly air-tight, air will leak through breaches in the wall assembly, usually at joints between different cladding components. The testing employs the basic principle that the air flow rate in through the blower doors will be the same as the aggregate air flow out through all the leaks in the building enclosure, and vice versa. Advanced computer software enables Halsall to check readings in real time. In the case of the OAA, for example, we could tell right away when a door was opened because the computer display would show a sudden pressure drop.
The total air flow through the building enclosure can be expressed in a number of ways. We can divide it by the total wall/roof area to help compare the results to other buildings of different sizes (benchmarking). We can also convert the total air flow to an equivalent size hole through the building enclosure. This effectively combines the area of all the small holes and cracks into one aggregate hole, which helps one visualise the amount of air leakage.
For the second part of the test – to actually identify the air leakage locations – Halsall conducted a thermographic scan. The building is first scanned while the interior space is being pressurized, then again while undergoing depressurization. When the outside temperature is cool, so are the exterior wall surfaces. Interior air that leaks out will warm up nearby cladding components and produce a “heat signature” that can be detected with infrared equipment. The pressurized and depressurized scan results are then compared. As Halsall Project Principal Dave De Rose explained to the assembled audience, “If the hot spots appear the same under positive and negative pressure, this indicates a thermal bridge. If the readings are different, there is air leakage.”
How air tight is the OAA building?
If you add up all the small cracks and holes in the building enclosure, the combined hole is about one quarter of a square metre. In other terms this is the same as 0.91 L/s of air flowing through each square meter of the building enclosure when a pressure of 75 Pascals is induced across it.
On its own, this raw result may not mean much. But when benchmarked against industry guidelines, the OAA office building is performing well. The building has 30% less air leakage through the building enclosure than the US Army Corps of Engineers (USACE) standard. This is a very strict standard that governs construction of all new U.S. Army buildings. (See the graph for the full set of benchmarked results.)
The thermographic scan did, however, pinpoint a number of isolated areas throughout the building enclosure where air leakage is occurring. While these isolated leaks do not have a significant impact on the overall air leakage, these breaches could be contributing to local areas of concealed deterioration. Where there is air leakage, there is a greater risk of condensation, which can result in metal corrosion or mould.
The testing also showed that air leakage was occurring through the mechanical system dampers when they are in the closed position and around some of the dampers/ducts where they penetrate the enclosure. The impact of this air leakage is significant. The volume of air leaking through these components when they are closed was the same as 66% of the air leakage through the rest of the entire building enclosure.
What did the test results mean for OAA’s building management strategy?
The full building air leakage test provided the architect and building owners with accurate, detailed information to help them focus their building management strategy.
Given how air tight the building enclosure was shown to be, Halsall recommended against large scale building enclosure air sealing retrofits as this would result in only marginal gains in energy performance. Instead, we advised the OAA to focus on adjusting or replacing the mechanical dampers and on sealing isolated air leaks. This strategy is expected to have better energy saving results and also improve the building enclosure durability.
Air leakage testing helps owners understand their building. Knowing how your building is performing allows you to make educated management decisions and choose appropriate remedial actions. In short, you can plan for the right repairs at the right time. Conscientious owners who want to reduce their carbon footprint, improve occupant comfort, and protect their asset for the future should consider full building air leakage testing to find out how their building really stacks up.
Jake Smith is a Project Manager with Halsall Associates’ Restoration team. Halsall is a national building engineering firm with over 50 years’ experience in designing, evaluating and renewing buildings. Contact Jake at firstname.lastname@example.org