May 21, 2020
By Austin Todd, CPHC, CEA, and Greg Labbe, CEA, CET
The drive toward a low-carbon environment means construction professionals are constantly refining the details of high-performance buildings. Though the industry is developing new materials to help achieve this, assembling airtight buildings is still a challenge. New and innovative air barriers are available for builders, but the challenge of integrating an air barrier system (ABS) comprising many connecting components requires attentive and caring tradespersons.
Performing airtightness testing on Part 3 buildings has been limited to high-performance projects. However, there is now a trend of mandatory airtightness testing in North America. With the third version, the Toronto Green Standard (TGS) almost catches up with industry peers in Europe, Washington State, and British Columbia in requiring whole-building airtightness testing of Tier 2, 3, and 4 buildings. TGS works similarly to the B.C. Energy Step Code, and in 2022, Tier 2 will replace Tier 1, meaning mandatory testing is on the horizon. Since there is no set airtightness target threshold, it is widely expected the most progressive builders will want to fix relatively easy test goals.
While a standalone airtightness test can be beneficial in quantifying building performance and serving as an opportunity to identify deficiencies in the ABS, it is most effective when combined with an envelope commissioning strategy. The envelope commissioning process involves:
The resulting periodic site visits to inspect the ABS along with physical testing of its components inevitably leads to greater consistency, higher quality, and results in improved building efficiency, comfort, durability, and better indoor air quality (IAQ).
It is well-known when buildings are more airtight, occupants experience greater comfort, IAQ is higher, durability increases, and liability is reduced for owners. The ultimate and quantifiable goal, though, is decreased energy consumption in the built environment.
An enclosure commissioning process is similar to a mechanical system commissioning process in that the enclosure is tested to qualitatively and quantifiably assess its integrity. If issues arise during the construction phase, changes are implemented to optimize assembly and performance of the ABS, leading to fewer future problems. Additionally, identifying and remediating deficiencies during the construction phase means the cost of these repairs is likely to be lower.
Current practices often produce inconsistent building enclosure detailing that can leave owners vulnerable to premature repairs due to condensation or moisture issues. Occupants are also affected, as they suffer from increased discomfort, street-level noise, and reduced air quality—all due to poor ABS detailing. Adding insult to injury, mechanical systems are typically designed to include a padded estimate for heat lost through the enclosure due to uncontrolled air leakage, leading to larger and possibly more expensive-than-necessary assemblies. Reducing uncontrolled air leakage lowers condensation risk and offers greater energy efficiency (Figure 1).
The benefits of adding more insulation in building enclosures are numerous, especially when the insulation layers are in intimate contact with the ABS. However, the benefits are squandered if there are gaps in the insulation or bypasses for air leakage. Thicker layers of insulation can leave a building vulnerable to unexpected and unwanted water vapour buildup driven by moisture-laden air leakage entering poorly connected ABS and getting into wall, soffit, or roof assemblies. Installing additional insulation to an envelope, even one that has been effective previously, can impact the location of the dewpoint in the assembly. If fuelled by an uncontrolled air leak, the condensation at the dewpoint can lead to significant moisture-related issues in the wall assembly.
Exhaust-only ventilation systems have been replaced by balanced, heat recovery systems in new construction, and these more expensive ventilation systems earn their keep if the building is airtight.
The most widely adaptable test method is the newly released ASTM E3158-18, Standard Test Method for Measuring the Air Leakage Rate of a Large or Multizone Building. Unlike previous standards, ASTM E3158-18 gives the agency guidance for evaluation during colder conditions and guarded testing. The standard methodology can be applied to all typologies of buildings from low-rise, stacked townhomes to high-rise commercials.
ASTM E3158-18 also distinguishes between an Operational or ‘as-operated’ test and Building Envelope or ‘as-is’ tests. The former is used to assess the building in its natural or as-operated state, and the results are utilized as inputs in energy models.
A Building Envelope test requires temporarily masking ventilation openings to measure the leakage rate of the building’s enclosure while removing leakage through mechanical systems from the results. This kind of test is usually used to meet the requirements of a building performance standard like EnergyStar or Passive House (PH or its U.S. version, PHIUS). Currently, TGS does not make a distinction between the two tests. Since the as-operated test method is less onerous, it will likely be the most specified one.
Testing to quantify the building’s air leakage rate is performed at substantial completion of the ABS, prior to occupancy. Some standards (e.g. PH) require testing at this phase to verify the building’s air leakage rate is below the acceptable certification threshold. If the building is not within the limits, additional air sealing work and tests would be required.
The building must be unoccupied on test day, with no trades or residents opening and closing exterior windows and doors. Prep work depends on the specifics of the test and the building type. This includes sealing mechanical vents and placing of blower door fans to keep the pressure uniform throughout the entire building. Typically, the enclosure consultant, project manager, and site supervisors are onsite to take notes on ABS deficiencies that need to be addressed prior to the final airtightness test. Ideally, even large buildings are tested as one whole ‘zone’ prior to occupancy, as was done with the 39-storey Incity building in Lyon, France, the Amazon Distribution Centre in Warsaw, Poland, and a 20-storey residential apartment building in Hamilton.
An alternative to single zone or whole-building airtightness testing is to evaluate sections of the building using the Guarded Testing technique. Guarded blower door testing is utilized when the whole building cannot be tested as one zone. The process involves isolating a representative section of the building, which is then sealed off temporarily from adjacent areas of the building, and all are tested at the same time (e.g. testing a single level of a multi-storey building when assessing the full building is impossible). However, it is unknown if the leakage through the isolated section of envelope accurately extrapolates to the full-building results—more on-field research is required. To this end, multiple guarded tests are being conducted during the construction phase of a high-performance, high-rise retrofit in Ontario. This will be followed by a final whole-building airtightness test. This project may provide insights on the feasibility of extrapolating data from one level to the whole building.
When to test
The authors’ recommendation is to test early, and often. As architect Tom Knezic suggests, it is best to plan for testing by including it in the critical path method diagram or in the Gantt charts. Ideally, all components of ABS are accessible during the test so repairs can be made as required, meaning during the construction process. However, whole-building testing is next to impossible in high rises, as the bottom third of the building is usually fully occupied before the top third is even enclosed. Therefore, some flexibility is expected on the part of the municipality because several guarded tests of a few representative floors are performed as the building sections are completed.
Most of the air leakage occurs where different components of the ABS come together, such as electrical, mechanical, plumbing, structural, and communication cable penetrations. Additionally, transitions at the roof-to-wall membrane, wall-to-soffit, and below-grade to above-grade wall can also be challenging. Simple visual inspection of the integrity of the seal between ABS components is a good start to ensuring the continuity of the air barrier system.
The transition joint between fenestration products and the rough openings is also a source of air leakage. Even if some windows are tested for air leakage, as per ASTM E783, Standard Test Method for Field Measurement of Air Leakage Through Installed Exterior Windows and Doors, and meet the requirements, the testing only measures air leakage through the fenestration product and not the integrity of the connection between the fenestration and the rough opening. The testing agency can quantitatively and separately test both and make recommendations on how to remediate the transition joint if excessive air leakage is measured.
Mockup testing can be used to verify airtight performance early in the project so changes can be made, if necessary. It is advisable to plan regular assessments of sections and use qualitative testing of ABS. Using ASTM 1186-03, Standard Practice for Air Leakage Site detection in Building Envelopes and Air Barrier Systems, air leaks in the ABS can be detected by employing theatrical fog or infrared thermography to pinpoint air leaks before they get covered in drywall, insulation, drop soffit, or brick. Once ABS is covered, repairs to make the envelope more airtight become prohibitively expensive.
As-operated testing and long-term airtight performance relies heavily on mechanically controlled dampers to control air leakage through mechanical systems. Rest assured, not all mechanically controlled dampers close well to seal under pressure, so selecting high-quality, remote-controlled damper systems in HVAC appliances ensures the lowest possible air leakage rate.
Specifications of tests
There are many ways to measure air leakage rates of buildings, and specifications are prone to misinterpretation by those with limited knowledge of airtightness testing. It is generally considered best practice to consult a testing agency with experience in evaluating large buildings. A building envelope consultant can help an architect set the bar, and will work with site supervisors and trades in the planning and construction phases.
Unless airtightness testing is mandated by a building code in a given municipality, or the project is aiming for a certification requiring airtightness testing, all testing will be voluntary, and is usually completed as part of a building envelope commissioning or quality control process. An airtightness test can be written into the project specifications by indicating:
It is common for airtightness specifications to be misquoted, but bringing experienced testers into the process as early as the specification writing stage can be beneficial. The way building scientists typically measure air leakage in small versus large buildings, for example, differs. In small, Part 9 buildings, the air leakage is proportional or normalized to the conditioned volume and is communicated as air changes per hour (ach) 50 or @50 Pa. In large buildings, however, the leakage rate is normalized to all six sides of the surface area, including slab, soffit, roof, above- and below-grade walls, and window areas, and is communicated as litres per second per square metre of envelope surface area (L/s∙m2). The metrics can get confusing, so special attention must be paid to them. One can reference the metric to imperial conversion tables in the Illustrated Guide to Achieving Airtight Building by B.C. Housing.
For comparison, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1-11, Energy Standard for Buildings Except Low-Rise Residential Buildings, deems a building airtight if leakage rate is below 0.5 L/s∙m2 (0.1 cfm/sf) @75Pa, and average building air leakage rate is below 1.5 L/s∙m2 (0.3 cfm/sf) @75Pa, and leaky is 3 L/s∙m2 (0.6 cfm/sf) @75Pa.
Codes and certifications mandating airtightness testing include the Washington State Building Code (SBC), B.C. Energy Step Code, TGS v3, Leadership in Energy and Environmental Design (LEED), EnergyStar Multifamily High-rise Pilot, and Passive House.
Several years ago, Washington State introduced mandatory testing for all buildings with a voluntary target. This acted as a ‘soft push’ for the industry to move toward high-performance building.
For Part 3 residential buildings, LEED has a credit for single-unit compartmentalization airtightness testing with a mandatory minimum performance threshold. The EnergyStar for Multifamily High-rise Pilot Program in Ontario has taken this one step further, requiring not only compartmentalization testing, but also whole-building airtightness testing. Airtightness testing is also required when energy code compliance modelling claims credit for improved airtightness metrics.
It is anticipated with the shift toward performance-driven approaches to energy efficiency in buildings in an attempt to reduce carbon emissions, mandatory testing enforced by either building codes or project owners will become commonplace.
Presently, TGS does not specify a target air leakage rate. To prevent undue hardship for the building industry while also bringing up the quality of building stock in Toronto, it is likely an airtightness performance threshold will be introduced eventually. Nothing currently prevents building owners from setting their own performance thresholds and committing the construction team to a higher standard like Passive House, which sets one of the most stringent leakage rates (the Passive House Institute U.S. (PHIUS) airtightness requirements have been adjusted from a limit of 0.6 air changes per hour [ACH] 50 for Part 9 and from 0.02 L/s [0.05 cfm] 50 and 0.04 L/s [0.08 cfm] 75 per square foot of gross envelope area for the high-rise residential, commercial, and institutional sectors). Achieving building airtightness does not require a transformation in process or new technologies, but rather a change in work culture that consistently focuses on the small details needed to assemble a continuous ABS.
Austin Todd, CPHC, CEA, is the cofounder of the consulting firm CoEfficient Building Science, and focuses on business development in both the residential and the commercial sector. A building science enthusiast, Todd is committed to accelerating the transition to a zero-carbon built environment. He is on the board of Passive Buildings Canada. Todd can be reached at email@example.com.
Greg Labbe, CEA, CET, runs the building science laboratory for the Graduate Studies programs at Ryerson University, Toronto. He also does contract work with Russell Richman Consulting Ltd. Labbe specialises in non-destructive testing of building enclosures, with a specialty in large building airtightness/air leakage testing using multiple, computer-controlled and logged blower door fans. He can be reached at firstname.lastname@example.org.
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