Curtain wall systems provide excellent access to daylight and views that are desired by the building owners and occupants for health and productivity. However, the increasing stringency of building codes has created a conflict with delivering highly glazed buildings because the glazed areas are less thermally efficient than opaque walls.
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Energy and thermal performance requirements are growing and playing an increasingly significant role in building codes throughout North America. However, understanding and meeting these requirements has also become complex for designers. At the same time, it is clear important decisions regarding basic enclosure assembly design and window area need to be made early in the project to achieve the most cost-effective, energy-efficient, and comfortable building.
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There is perhaps no building element that typifies contemporary architecture more than the curtain wall. Lightweight and flexible, these glazed assemblies not only allow more usable floor space within a building, but also epitomize upscale, modern construction.
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Energy efficiency, green construction, increased insulation, net-zero—all these terms imply the same expectation: to improve the performance of buildings and minimize their impact on the environment by reducing greenhouse gas (GHG) emissions, conserving natural resources, and maximizing the service life of all building systems—all while maintaining comfortable and functional buildings.
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Canadian energy codes will never be less stringent than they are today. Therefore, it is important to have a firm understanding of the building options available to achieve and outperform regulations. Contrary to some conventional thinking, a ‘systems’ approach to construction can prove an ideal building approach even when high thermal performance is required.
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Reducing the operational energy use and increasing durability should be the prime concerns of architects who wish to design and build ‘green’ buildings,” wrote John Straube, PhD, P.Eng., principal at RDH Building Science and RDH Building Science Labs.
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The 2015 National Building Code of Canada (NBC) brought about multiple changes. One of the most important from an insulation standpoint is the treatment of the language concerning RSI values. (Although most in the construction industry are more familiar with the term ‘R-value,’ this article will use the metric values RSI for insulation.)
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Although many advances over the last decade have improved energy efficiency, not every new building is designed and built with these technologies. In some other instances, older buildings that have undergone retrofits have better thermal control capabilities than newer structures.
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Insulation placed in the exterior air cavity between brick veneer and a backup wall is now common practice; however, accounting for the reduction in thermal performance as a result of thermal bridging at brick ties is not. As the building enclosure’s actual thermal performance becomes more important and integrated into the overall design of other building systems, a clear understanding of thermal bridging and its impact on effective R-values is needed. Brick ties are only one example of a thermal bridge in the building enclosure, but a close look at their significance illustrates how important it is to account for thermal bridging.
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A study by Pennsylvania Housing Research Center (PHRC) showed significant reductions in centre-of-cavity R-value for steel-framed wall assemblies, reducing it by as much as 56 per cent when a framing factor (i.e. thermal bridging) was taken into account to measure R-value.
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