Fenestration Review

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FGIA: Let’s stop the pendulum


October 21, 2021
By Amy Roberts, FGIA director of Canadian and technical glass operations

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Over the past half century or so, the preferred design approaches for energy-efficient construction have swung back and forth between restricting window-to-wall ratio and maximizing daylighting to reduce the lighting energy budget. It looks like another swing of the pendulum is underway. The development of the 2020 Canadian National Energy Code for Buildings (NECB) included a code change request (PCF 1541) to reduce the maximum allowable fenestration and door-to wall ratio, primarily in commercial buildings. 

The proposed code change, submitted by the Standing Committee on Energy Efficiency (SC-EE), was to significantly reduce the allowable glazed area in different Canadian climate zones. However, experience shows that reducing lighting energy, which often comprises the bulk of energy consumption in commercial buildings, is a more valid way to improve energy efficiency than reducing building envelope U-factor. FGIA took the position that this proposal was out of step with today’s high-performing fenestration products, and would have a number of negative impacts. 

First, it ignored potential harm to occupant performance, health and well-being. The Illuminating Engineering Society has noted that people in modern societies spend 95 percent of their lives indoors. This highlights the importance of the physiological and cognitive effects of daylighting, revealed by several studies conducted in the early 2000s. These studies quantified the surprising degree by which students, employees and hospital patients perform better in a daylit environment. In retail settings, increased sales and more transactions are the result.  

The proposal’s cost-effectiveness analysis does not consider negative financial and economic impacts on building owners. In addition to light quantity and quality issues, all facilities with judiciously designed daylighting can save significant operating costs in the form of decreased electricity demand. A lack of daylighting can thereby increase costs while lessening desirability, adversely affecting property values and rental rates.

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The proposal conflicts with precedents in other energy and green building standards and credits. These include model energy conservation and green building codes such as ASHRAE 90.1, the International Green Construction Code, ASHRAE 189.1, and LEED Daylighting and View credits.

Finally, the proposal threatened design flexibility without adequate justification. Codifying lower window/wall ratios discourages architects from seeking ways to maximize daylighting for the benefit of building occupants while minimizing heat transmission, such as by using new high-performance glazing products, such as spectrally-selective low-E glass, triple glazing, vacuum insulating glass or dynamic glazing. It also forecloses options for increased occupant comfort, connection to outdoors, esthetics and real estate value, with disparate impact on small retailers and owners. 

All-in-all, a balanced systems approach in which a designer melds all aspects of a building to maximum effect has always been the best answer. The NECB already provides for this with trade-off and performance paths, which are being increasingly used with commercial buildings. 

For these reasons, FGIA recommends following the ASHRAE 90.1 window-to-wall ratio of 40 percent. This would promote harmonization for the industry as a whole, while not following this recommendation could create a significant barrier to trade. 

Based on this rationale, the industry was successful in stopping the code change proposal from going forward in the 2020 NECB. However, the SC-EE will be looking at other ways to drive further energy savings in future codes, and the industry will need to monitor this activity closely.