CAN/ULC-S742 is entitled “Standard for Air Barrier Assemblies—Specification” and covers the air barrier assemblies (a combination of air barrier materials and their accessories) used in low-rise and high-rise buildings. Similarly to S741, it includes test conditions to measure the air leakage rate of an air barrier assembly’s representative specimen and defines the performance level that must be attained. Each tested assembly is then given a classification (A1 to A5) that is based on its air leakage rate at a reference pressure difference, measured before and after exposure to cyclic wind loading.
The testing detailed in S742 references the testing methods and procedures found in ASTM E2357. The air barrier assembly being tested is mounted in two different 2.4 m by 2.4 m frames. The test specimens must be representative of the air barrier assemblies as constructed in the field and according to the manufacturer’s installation instructions. This includes the use of primer when applicable, the proper sealing of laps, and perimeter reinforcement if required.
In the first frame, the assembly is installed without any penetration of the air barrier materials. Side and end laps must be present in the case of discontinuous air barrier materials (sheet-applied materials or panels). In the second frame, various penetrations typically found in an exterior wall are added to the assembly: window, galvanized steel duct, pipe, junction boxes, and brick ties, for example. All penetrations must be sealed with appropriate accessory material to maintain continuity of the plane of air tightness. Figure 1 shows a frame with all penetrations sealed and ready to be tested.
Both frames are then tested individually. For testing, each frame is placed between two climatic chambers, and a computer-controlled system allows the operator to generate a pressure difference (infiltration and exfiltration) across the frame and the air barrier assembly. The pressure difference varies from 25 to 300 Pa during the test, and the air leakage rate across the assembly is measured and reported at a pressure difference of 75 Pa.
This is where S742 and ASTM E2357 part ways. After being subjected to this first test, each frame is exposed to a series of pressure differences (infiltration and exfiltration) simulating cyclic wind loads. Static pressures starting at 450 Pa are maintained for one hour. Next, cyclic pressure loads and gust loads reaching at least 980 Pa are applied to each frame. Deflection of the air barrier assembly is measured during this portion of the test, which provides professionals with guidance on the selection of materials.
Air leakage rate measurement is then repeated twice on each frame. The first measurement is performed under typical laboratory conditions (identical to the test prior to cyclic loading). The second measurement is performed under “winter” conditions, where a temperature difference is induced across the frame. In this case, the exterior side of the assembly is cooled to -20 °C while the interior side is maintained at 20 °C. For an air barrier assembly to obtain the A1 classification (the most stringent classification), the largest air leakage rate measured in all the above conditions cannot exceed 0.05 L/s•m² at a pressure difference of 75 Pa.