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The Engineer: Case solved

I think we need to be taking the ROI question a few steps further and consider not only the financial return on investment but also the social and environmental factors.


March 3, 2021
By David Heska

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Happy New Year to all of our Glass Canada readers! I hope you had a restful and enjoyable time off and that you were able to be active outside during the holiday season. Everyone in my family was up bright and early on Christmas Day and the fresh snow allowed us to put our new toboggan and GT Snowracer to immediate use. A few days later I picked up a fictional mystery novel and was able to quickly read through it. Everyone loves a mystery case solved, right?

In my December column I presented a recent project case study example that I have been working on for a two-storey warehouse and office building constructed 40 years ago. The client knew that their aging windows needed to be replaced and hired us to complete an evaluation. We presented them with three options. Option one: refinish the frames and install new double glazed IGUs. Option two: replace the entire window system with a new double-glazed system. Option three: replace the entire window system with a new triple -lazed system.

I have received many emails and comments related to this example. One person suggested “Start with a high-performance frame. Some double-glazed windows perform better than triple-glazed”. Another person stated “What is the capital outlay for each option? What is the difference in the insulating values? What is the life cycle of each?” These are all great points. It is true that there are some double-glazed windows that are better than triple-glazed, and answering the return on investment question is always valid. I think we need to be taking the ROI question a few steps further and consider not only the financial return on investment but also the social and environmental factors.  For example, what is the embodied and operational carbon comparison for the three options outlined above? Which is the most sustainable and durable?

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In the end the client decided to proceed with the second option: to replace the entire window system with a new double-glazed system. This option was chosen in part because the majority of the building enclosure is the roof. In fact, the roof represents 85 percent of the enclosure area. Fourteen percent of the building enclosure is brick wall and less than one percent is windows. Using simplified modelling, we determined that the existing enclosure had an insulating value of approximately R13. (Please note this insulating R-value is well below current code requirements, but small-scale retrofits typically do not have to comply with current code). We presented the client the modelling results that showed by upgrading to a triple-glazed system we would only be able to achieve an improvement to R14.

If the windows represented more than just one percent of the building enclosure, or if the client wanted to consider a complete enclosure renewal, our recommendation would likely have been different. But in this case the double-glazed option was selected. Our design specified a high performance five-inch frame, new double-glazed windows with argon glass fill, a low E coating on surface #2 and a thin-wall stainless steel spacer. The specified frame options allow for triple-glazed IGUs if at some point in the future the client wants to upgrade. The building permit is currently being obtained and construction will begin in April.


David Heska, P.Eng. is a director with WSP’s building sciences team in southwestern Ontario. He oversees the operation of the Hamilton, Kitchener and Windsor offices. David has been involved on window simulation projects as well as the design and replacement of windows. He can be reached at David.Heska@wsp.com.


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