Glass Canada • June 2025 • One number

Successive Canadian governments have wanted Canada to do its part to slow or stop climate change by reducing the amount of carbon dioxide we put into the atmosphere. Key to that effort is an effort to reduce the amount of CO2 produced to build, maintain and operate our buildings, which have been identified as being responsible for about 40 percent of Canadian emissions. As providers of glazed facades, we’ve been called upon to do what we can to assist in that effort. Here’s what that effort looks like as a matter of practical reality.

Every year, at every glass industry conference, a technical analyst or building science guru gets up in front of the audience and presents a series of eye-watering slides. On each are rows of numbers arranged into columns and tables. These numbers show the allowable values for various aspects of a building’s glazing: thermal transmission through the centre of glass; thermal transmission through the whole assembly; airtightness and solar heat gain. There will be different numbers for airtightness depending on the elevation of the installation, the amount of obstructions around the project and the expected wind load in the area. There will be different numbers for solar heat gain depending on the region the installation is in and the number of heating days it experiences.

There will be one set of these numbers coming from the National Energy Code for Buildings. Depending what province your product is going to, there may be another set of these numbers overriding them. If you are in a big municipality, there may be yet another set of these numbers. In most cases, there are up to four more duplicate sets of numbers reflecting different tiered compliance paths the project can follow.

To verify whether your assembly meets any of these numbers, you need to follow testing and certification methods set out by the National Fenestration Research Council, the Canadian Standards Association and/or the Fenestration and Glazing Industry Alliance. This involves more rows and slides showing numbers for the testing sizes and conditions like wind and water pressure, temperature on either side of the assembly, IG fill level and more.

All of these rows and columns of numbers will then be accompanied by further rows and columns showing what the numbers were in the past and what they either have changed to or will change to in the near future. Each changed number will require at least an analysis by an engineer to make sure the fabricator’s present designs comply. In some cases they will require re-testing. In some cases they will require a full redesign. The production of the numbers themselves – old and new, here and there – reflects thousands of hours of work by industry committees, engineers and codes and standards officials.

All of these numbers and efforts add up to one thing: regulating the degree of insulation provided by the glazed portions of a building facade. They are relevant to carbon dioxide emissions to the extent that the insulating value of the facade reduces the emissions produced to create energy for the building. If the building is heated and cooled by electric-powered HVAC equipment, and if the electricity is produced by wind, solar, hydroelectric or nuclear sources, all of the above numbers become almost completely irrelevant to the building’s impact on climate change. Electrification of HVAC systems is a significant focus of the Canada Green Buildings Strategy, with incentives in place to encourage heat pumps and solar power in ICI projects. It’s likely we’ll see natural gas and oil heating phased out over the coming decades.

There is one number that matters to the question of climate change: the amount of carbon dioxide (there are other greenhouse gases, but CO2 is the major concern) released into the atmosphere as a result of a building’s existence. Where in the world the CO2 is released doesn’t matter. How it is released doesn’t matter. When it is released doesn’t matter when we understand that the goal is to permanently reduce the amount of CO2 we release. Yes, CO2 released in the future is not warming the planet today. But it will when it does, so simply delaying release is of little benefit. The relevant metric is the total CO2 released over the lifespan of a building as a result of its construction, use and eventual demolition.

By now, most of us are probably familiar with the chart showing stages A through C of the building lifecycle that identifies the different ways a building project releases CO2 through time. The only true metric of the building’s contribution to climate change is the one number for carbon dioxide release that results from measurement of all the inputs on that chart. All of them – from extraction of raw materials through disposal of the demolished building and everything in between. With no compartmentalization of the various building components such as facade, mechanical, structural, electrical and infrastructure.

Yet for the better part of 50 years now, the research and development focus in our industry has looked like the number-filled conference rooms described above. That’s because governments have been engaged in an on-again-off-again program to nudge the glazing industry down the path to more insulating products. It’s required decades of committees, research and standards development, building incremental change cycle after cycle, for one simple reason: the market hasn’t demanded it. The jury is back and the verdict delivered – people will not pay a nickel extra for energy-efficient buildings unless the energy savings pencil out to overall savings. And do so within a time frame when the owner still expects to own the building. In the case of most commercial and condominium builds, that time frame is zero. Absent a market incentive to boost energy efficiency, the only alternative for governments has been regulation, carefully phased in so as to not depress construction activity. Thus the endless slides full of numbers that shift a few decimal points year by year. Thus the wrangles over metrics and methods (ER versus U-value? Standard sizes versus algorithms?). Thus the parade of shifting goalposts.

And thus a focus that has amounted to a colossal false-start for reduced carbon building. It is only in the last 15 years or so that standards writers have started to focus on embodied carbon, developing the framework for product category rules that can define how much carbon is emitted in the manufacture of a glazed assembly. It’s only in the last 10 years that code officials have begun to signal that they will begin to phase embodied carbon reporting, then limits, into the nation’s building codes. Yes, LEED existed before that and did establish a holistic framework for determining a building’s overall carbon contribution, but it includes a suite of other environmental factors (contribution to ocean acidification, use of finite resources, the “healthiness” of the indoor environment) and is a voluntary certification. So it never enjoyed widespread adoption, though parts of it may serve as a roadmap forward for the vision expressed here. What has happened on the ground is that building engineers in Canada and around the world have spent at least 30 years driving innovation in reducing operational carbon only to be faced today with the need to at least put a significant additional consideration into their designs. In some cases, considering embodied carbon will require revisions to existing designs. In others, it may actually require tearing up designs entirely or even opting for less-insulating glazing.

The infamous example is triple glazing. In the tiered energy codes introduced in the 2020 NECB (which followed B.C.’s Step Code in 2017), the highest levels of energy performance called for a centre-ofglass U-value of 0.82. This was a rating really only achievable with vacuum insulating glass (too expensive and not available in quantities at the time) or triple-glazed insulating glass with low-E coatings. Provinces and municipalities signalled their intentions to phase in progressively higher tiers for compliance. Today, it is still the stated intention of Natural Resources Canada’s Green Building Strategy to mandate the highest tier by 2032. Accordingly, R&D departments in fenestration manufacturers across the country have scrambled to design, develop and test triple-glazed products so they can meet market demand when the code requires it.

But triple-glazed fenestration uses more glass. One-third more, to be specific. The glass production process is highly carbonintensive, releasing tons of CO2 to produce the 1,500-degree temperatures required. Triple glazing requires larger frames, using more framing material. Fenestration framing material, especially aluminum, is very carbon-intensive to produce. Triple-glazed assemblies are also heavier and more awkward to install, possible requiring the use of carbon-emitting machinery where none was needed before.

So while the triple-glazed facade may save some operational carbon over the life of a building, it introduces a significant embodied carbon cost up front. In buildings powered by low-carbon energy sources, as discussed above, operational carbon savings may have little impact on the overall carbon budget of the project. Analysis by Claudio Sacilotto of Novatech suggests that, in Ontario’s energy grid, it would take 25 years of operational carbon savings to offset the additional embodied carbon introduced by installing tripleglazed vinyl windows in a residence versus double-glazed – even if the residence was heated by natural gas.

By lasering in on operational carbon ever since the oil crisis of the 1970s, construction technology development in this country has gone in generally the right direction, but by the wrong route. Consequently, without changing the path, it will never arrive at its precise destination of a built environment that generates the lowest possible carbon release. No question, the development of more insulating facades has been beneficial and will be beneficial to the extent that buildings generate lower carbon emissions from fossil fuel use to power them. It is also beneficial to the extent that property owners have experienced and will experience lower energy costs – however property owners have voted with their wallets on that front, clearly preferring saving money on upfront engineering today over saving energy costs tomorrow. But by ignoring embodied carbon for decades, and embarking on regulatory regimes without it, governments have forced untold millions of dollars in R&D and process investment that will now need to be at least partially unwound. It’s as if they told us to build cars that would go as fast as possible, but never allowed for the need to upgrade the brakes.

And another directional wrong-turn looms. We are still in the early phases of introducing embodied carbon to our codes and standards. But already another word is gaining volume in building science circles: resiliency. Resiliency assesses a building’s likely useful longevity and its propensity to be repaired, maintained, upgraded and even recycled over time. In one sense, it is an outgrowth of embodied carbon life cycle analysis, since the objective of a more resilient building is to avoid having to release CO2 by manufacturing new components for it or demolishing it entirely and building a new one. But resiliency also addresses the need for buildings of the future to withstand the effects of climate change, including more frequent extreme weather events and different conditions in the regions where they are designed and built. So in some cases the need for resiliency could be in tension with embodied and operational carbon calculations. What if you designed a facade made out of bamboo that achieved the lowest overall carbon release because the building was heated by solar power? Let’s say the facade is so carbon-friendly that you could replace it entirely every 20 years and still have a net gain on the carbon budget. But it doesn’t hold up too well through freeze/thaw cycles. If temperatures fluctuate too much in the winter, it will only last 10 years. By focusing on operational efficiency and low embodied carbon, but ignoring resiliency, you’ve made a facade that is not optimized to minimize carbon release.

On the next leg of our journey toward a minimum-carbon built environment, we should avoid taking off down the wrong path in the right direction again. We should load into our GPS the final destination – the lowest possible carbon release as a result of a building project – and follow that route. We should replace all the slides full of numbers with one number.

Denmark is close to doing this. According to an Aalborg University report, Climate Impact from New Construction, (thanks to Juliette Cook of Half Climate Design for the information) it’s Department of Built Environment has established a limit of 12 kilograms of CO2 released per year per meter squared of structure. That number includes manufacture of the products, replacement of building components, operational energy use and end-of-life demolition and disposal (chart sectors A1-3, B4, B6 and C3-4). Denmark plans to add sectors A4-5 (construction and installation activities) as a separate calculation capped at 1.5 kilograms emitted per meter squared per year. That’s it. Denmark doesn’t care what the building is made of, how insulating it is or is not, how airtight it is or how it is heated and cooled as long as it all adds up to something less than these carbonrelease targets.

The one-number system would place a limit for total annual carbon emissions from all sources on the building project, not the building itself or any individual component. The project owner would be required to submit a life cycle analysis for the whole project, from inception to its projected end of useful life, using approved sources of carbon-emission information for each stage. Approval of the LCA would be part of the permitting process and confirmation that the approved model had been followed would be part of the final inspection process. There would be no energy-efficiency or embodied carbon requirements on any particular part of the project. If the architect wanted to have open holes instead of windows and crank up the heat to compensate, that would be fine as long as they could show the overall carbon release didn’t exceed the limits. If they wanted to make the roof out of highcarbon steel but heat the building with sunlight and geothermal, they could do that as long as the project didn’t exceed its carbon budget. The one-number system would unlock absolute maximum design flexibility for architecture and maximum potential for innovation in finding ways to hit aggressive carbon targets under budget.

For glass fabricators, little would change except for the need for product engineers to spend hours looking at slides full of numbers from various jurisdictions’ energy regulations. For standardized products, they would develop good, better, best energy efficiency options and attach test results generated at test labs (using whatever sizes and configurations they want) and EPDs compiled using EPDs from their component suppliers. For custom projects, the EPDs from suppliers would be fed into software that generates the carbon load of the design and projects it over the expected life of the facade. Thermal transmission, solar heat gain and air/water tightness would be tested to spec as usual, with the difference that the target values would not be determined by a standard written a thousand kilometers away in a different decade. The glass fabricator would just provide these test numbers. Their impact on the operational carbon of the building would be assessed by the architect and used to contribute to the whole-building LCA.

Glazing contractors, having received the carbon impact numbers for the products from the fabricators, would need some way to produce a carbon impact statement for their shipment and installation activities. Much of this could come just from reasonable estimates of energy use on site for vehicles, lift equipment, heaters and generators. Generic numbers could even be used extrapolating from time spent at certain tasks. As in any energy regulation, the objective need not be actual, realworld, completely accurate measures of energy used and carbon emitted. Reasonable estimates and projections can do the trick, and are all that are practically possible anyway.

Under a one-number system, the responsibility for producing a carbon budget for a project would fall to the project owner as part of the design approval process. Architects will need to collect certified EPDs from their product suppliers – something most building component manufacturers are busy producing now –and use them to produce a budget for constructing their design. The project engineer would add data for the project infrastructure – roads, parking, utilities, landscaping, maintenance – and project those carbon costs forward over the expected life of the building using metrics like Energy Use Intensity. When all this data is integrated, the total amount of carbon dioxide released by the building project would then be known, and would be the sole determinant of whether the project meets government energy standards.

The big remaining barrier to easily producing project carbon budgets is software that can integrate all the inputs and generate the one number. These products are in development. the day is fast approaching when construction software platforms such as ProCore will have all the carbon release numbers for each element of a construction project attached, just as they have cost information attached today. From there, a full carbon budget for any project is just a click away, and can be updated by integrated AI whenever a parameter is changed. We should not underestimate the potential impact of such a system. A project engineer trying to get their carbon budget in under the target could play with literally any element of the project. Instead of going back to the glass fabricator and insisting on a two basis-point reduction in Uvalue of the glass, he could specify renting electric equipment on the job site. Instead of reducing window-to-wall ratio, he could specify a low-carbon cement or pave the parking lot with a non-asphalt-based product. Trade-offs that can’t be contemplated under the present performance-based regulation regimes, which are today solely focused on operational carbon, could come into play and unlock tremendous design creativity. Project owners would be able to design and build the projects they want and that their target markets demand. Developing better software design tools with integrated carbon cost information should be a request to digital suppliers from this industry and from governments.

A straw poll of industry experts by Glass Canada has revealed the major outstanding barrier to adoption of a onenumber regime: the lack of the necessary EPDs and approved methods for gathering and applying carbon-release information to generate the needed models (some of this feedback will be attached to the online version of this article). The present lack of capability in existing software tools noted above would be another practical barrier to adoption, as generating a whole-project carbon-release budget for every project could be an unreasonable burden without AI help. That’s why this article should be seen as an argument for a future direction for regulators rather than a call for immediate change. For too long, the North American effort to make construction more climate-friendly has proceeded without the end in mind, focusing on first this and then that individual element of the building. Years of R&D have been applied inefficiently to parts of the problem and resulted in some cases in downright counterproductive efforts. It’s time for those interested in making Canada’s built environment less impactful on climate change to look at each of their efforts and ask if they serve the ultimate goal in the best possible way.