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BCIT Tall Timber Student Housing project, Burnaby, B.C. Engineered Assemblies rear-ventilated rain screen with an active plenum. S E P T E M B E R 2 0 2 4 | 27 Building Enclosure Systems P H OTO G R A P H Y CO U RT E S Y T H E F LY N N G RO U P O F CO M PA N I E S; I L LUS T R AT I O N CO U RT E S Y EN G I N EER ED A SS EM B L I E S As energy regulations tighten, attention turns to building enclosure systems by ROBIN BRUNET W ith energy efficiency in buildings regulated to ever- increasing degrees, more focus than ever is being placed on the importance of building envelope systems (now sometimes referred to as building enclosure systems) in residential, commercial, and industrial design. The question of what system is superior has morphed into a more nuanced discussion about what system is the most desirable for a specific circumstance, with materials and their performance studied in great depth. Such is the case of Brian Hall, managing director at the Canadian Precast/Prestressed Concrete Institute, who cites the new endorsement from Pro-Demnity Insurance Company of Toronto (a liability insurer for architects) on precast concrete enclosures. "High-performance precast concrete enclosure systems stand apart from most rain screen walls in several key respects: controlling rain penetration, providing airtightness, and their construction sequence," says Hall. "Precast concrete has been used successfully to provide durable building enclosures for decades." Hall goes on to note that precast drained enclosure systems assume some rainwater will penetrate the outer surface (hence, the cladding screens the rain). "Therefore, the assembly must be designed to remove this water by pro- viding drainage, comprised of a capillary breaking drainage plane, a drainage gap, flashing, and weep hole/drain." One key advantage of prefabricated wall panels is their practicality. "Precast concrete architectural and double- wythe insulated wall panels are all examples of these practical, perfect barriers," Hall explains. "When designed as drained joints in the form of two-stage sealant joints or similar, the joints between these elements further enhance their effectiveness, providing reassurance of their efficiency." Jeff Ker, senior technical advisor at Engineered Assemblies Inc., points out that the ambiguous definition of rain screen systems in recent history has hindered the performance of many facades at a time when developers can't afford anything but great performance. Engineered Assemblies supplies world-class facade materials backed by leading expertise in rear-ventilated rain screen sub-structure assemblies, and Ker says a key problem that led to criticism of rain screen systems were the numer- ous definitions of the systems. "In this regard, Engineered Assemblies has been working on the technical committee of R AINA [Rainscreen Association in North America], which was founded in 2020 to establish a single definition," he says. "Properly designed and installed, rain screens belong everywhere and live up to the standards of the building envelope being a building's primary passive environmental control system, responsible for managing thermal and moisture control." Ker says R AINA is on the cusp of publishing a spec that will define a proper rain screen once and for all, thus helping to eliminate the numerous wrong ways such a system can be developed. "Ironically, the definition runs parallel to what we at Engineered Assemblies came up with 18 years ago, and it's satisfying to see this finally coming to light at a time when Passive House and other build- ing techniques are becoming more common. The fact is, ventilation is the only way to get rid of moisture in an interior environment, and the practice of sealing up a building is a nasty one because at some point the interior and exterior climates will meet, with bad results." Ker offers some insight into what makes the Engineered Assemblies rear-ventilated rain screen so effective. "Having an active plenum ensures the circulation of air is constant in good times and bad. The plenum can only function best when unobstructed and with the combination of adequate intake and exhaust vents. "Having adequate ventilation/air flow means the substruc- ture supporting the façade material can see a longer lifespan and the insulation can function at its maximum potential in its dry state. Also, placing a secondary drainage plane in front of the insulation [behind the plenum] will further thwart the intrusion of precipitation, minimize wind washing, and provide a visually pleasing veil to hide substructure and insulation through open joints of facade panels." THE GREAT BARRIER BRIEF

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